The goal of this work was to design and investigate the gain switched new Fe,Cr:ZnMgSe laser operating at the room
temperature. The pumping was provided by the electro-optically Q-switched Er:YAG laser with the oscillation
wavelength of 2.937 μm which matching the absorption line of the Fe,Cr:ZnMgSe crystal. The Q-switched operation
was obtained by the Brewster angle cut LiNbO3 Pockels cell placed between the rear mirror and the laser active medium.
The output radiation parameters were: the energy of 10 mJ, pulse duration of 120 ns, and repetition rate 1 Hz.
The pump radiation was directed into the Fe,Cr:ZnMgSe crystal placed inside the 16 mm long hemi-spherical cavity
formed by the dichroic pumping mirror (T = 86 % at 2.94 μm and R = 100% for 4 - 5 μm) and the output coupler with
the reflectance R = 95 % at 4 - 5 μm and radius of curvature r = 500 mm. The maximum output Fe,Cr:ZnMgSe laser
energy was 160 μJ corresponding the slope efficiency 4 % (with respect to absorbed energy). The generated radiation
wavelength was 4.8 μm with the linewidth of 100 nm (FWHM). The output beam spatial profile was approximately
Gaussian in both axes.
Laser tuning properties were investigated by the Lyot filter (MgF2 plate, 2 mm thick) inserted into the resonator
providing the tuning range from 4.5 to 4.9 μm. The results were compared with the Fe:ZnSe crystal operated at the same
conditions.
The aim of presented study was an investigation of tunability of diode pumped laser based on hot-pressed
Yb:CaF2 ceramics. The tested Yb:CaF2 sample was in the form of 3.5mm thick plane-parallel face-polished
plate (without AR coatings). The Yb3+ concentration was 5.5 %. A fiber (core diameter 200 μm, NA= 0.22)
coupled laser diode (LIMO, HLU25F200-980) with emission at wavelength 976 nm, was used for longitudinal
Yb:CaF2 pumping. The laser diode was operating in the pulsed regime (4 ms pulse length, 20 Hz repetition
rate). The duty-cycle 8% ensured a low thermal load even under the maximum diode pumping power amplitude
10W (crystal sample was only air-cooled). This radiation was focused into the crystal (pumping beam waist
diameter ~ 170 μm). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror
(HR @ 1.01 − 1.09 μm, HT @ 0.97 μm) and curved (r = 150mm) output coupler with a reflectivity of ~ 98%
@ 1.01 − 1.09 μm. Tuning of the ytterbium laser was accomplished by using a birefringent filter (single 1.5mm
thick quartz plate) placed inside the optical resonator at the Brewster angle between the output coupler and
the laser active medium. The extremely broad and smooth tuning was obtained. The laser was continuously
tunable over ~ 66nm (from 1015nm to 1081 nm) and the tuning band was mostly limited by free spectral range
of used birefringent filter. The tunability FWHM was 40 nm corresponding bandwidth 10 THz results in Fourier
limited gaussian pulse width ~ 40 fs (FWHM). The maximum output power amplitude 0.68W was obtained at
wavelength 1054nm for absorbed pump power amplitude 6W. The laser slope efficiency was 15%.
One of the promising active ions giving the possibility of laser radiation generation in 4 - 5 μm region is trivalent
dysprosium in lead thiogallate crystal. On the basis of our previous Dy3+:PbGa2S4 laser study, this work is showing a
several wavelengths generation possibility. The laser was working at the room temperature and it was in-band pumped
by the Er:YLF laser radiation with the wavelength 1.73 μm. The investigated crystal Dy3+:PbGa2S4 was synthesized
using Bridgman technique from the melt. Dimension of the sample was 16 mm long and 19 mm in diameter and the
nominal Dy3+ ion concentration was ~ 0.7 at. %. The laser operation was tested with three resonator configurations. The
first was the non-selective resonator with the length 41 mm. To perform the wavelength tuning, in the second case the
MgF2 Lyot filter was inserted under Brewster angle inside the resonator which length was 100 mm. In both these cases
the laser resonator was formed by the incoupling flat dichroic mirror with low reflectivity at pumping wavelength (T =
90%@1.73 μm) and high reflectivity (R~100%) within the 3.5 - 4.5 μm spectral range, and by an out-coupling concave
(r = 500 mm) mirror with reflectivity of 95 % or 98 % in the same region of wavelengths. For the third case the selective
mirrors supporting the 3.0 - 4.0 μm spectral region were chosen. The generation possibility on three lines 4 μm, 4.3 μm,
and 4.6 μm were found without continuous tuning between them.
The mid-infrared radiation generated by bulk Dy:PbGa2S4 laser working at room temperature was characterized and for
its delivery the special type of COP/Ag hollow waveguide was used. The optical pumping of Dy:PbGa2S4 laser was
performed by flashlamp pumped Er:YLF laser at 1.73 μm wavelength. The compact 60 mm long Dy:PbGa2S4 laser
oscillator worked in free-running mode with the repetition rate 1.5 Hz. The output energy was 5.1 mJ in 80 μs long pulse
at 4.3 μm wavelength. The spatial beam structure was close to the Gaussian shape.
The goal of the presented study was the preliminary investigation of the mid-infrared Dy:PbGa2S4 radiation delivery
possibility by the cyclic olefin polymer and silver coated hollow glass waveguide. The length of the waveguide was
103 cm and the inner diameter was 700 μm. The thickness of the polymer inner layer was calculated for the optimal
4 μm radiation transmission. Mid-infrared laser radiation was coupled into the waveguide by the CaF2 lens with the focal
length 55 mm. The characterization of delivered 4.3 μm radiation was provided. It was observed that the spatial structure
is changing essentially, which follows from the transmission principle of the hollow waveguide. As conclude the
delivery system for 4.3 μm mid-infrared Dy:PbGa2S4 laser radiation was investigated for the first time.
The aim of the presented project was comparison of two Fe:ZnSe lasers based on Fe:ZnSe bulk active crystals grown by
two different methods - Bridgman and floating zone. For pumping the Q-switched Er:YAG laser generating 15 mJ and
300 ns giant pulses was used. The highest Fe:ZnSe laser generated output energy was 1.2 - 1.3 mJ for both investigated
crystals, the pulse duration was 150 - 200 ns. The Fe:ZnSe laser threshold was reached at absorbed pumping energy of
~ 1 mJ. Tuning properties using intracavity CaF2 prism were also investigated and tuning range ~ 4 - 5 μm was observed
for both crystals.
A special type of Cyclic Olephin Polymer silver coated (COP/Ag) hollow waveguide was used for delivery of 4.45 μm
laser radiation. This mid-infrared radiation having major signification in special lidar or spectroscopy applications was
generated by new bulk Fe:ZnSe laser working at the room temperature in gain switched regime. The coherent pumping
of Fe:ZnSe laser was performed by electro-optically Q-switched Er:YAG laser which wavelength (2.94 μm) corresponds
to the maximum of Fe:ZnSe absorption peak. The Er:YAG laser energy and pulse-length used was 11 mJ and ~ 300 ns,
respectively. The generated Fe:ZnSe laser output energy was reached 1.1 mJ with the pulse-length 240 ns.
The aim of the presented project was to investigate the transmission possibility of 4.45 μm mid-infrared Fe:ZnSe
radiation by the COP/Ag hollow glass waveguide. The inner waveguide diameter was 700 μm and length 103 cm. Midinfrared
laser radiation was focused into the guidance protector by the CaF2 lens with the focal length 55 mm. After the
coupling Fe:ZnSe radiation optimization, the maximum transmission of radiation through the waveguide reached 64%.
The time evolution of the pulse was not changed by the delivery but the space structure is changing essentially. It follows
from the radiation transport principle of the hollow waveguide. The bent waveguide transmission was also investigated
and 60% was obtained. For the case of contact application the fused silica cap was performed. As conclude the compact
delivery system for 4.45 μm mid-infrared radiation with the short 240 ns pulse length and transmitted power density
0.57 MW/cm2 was successfully investigated and it can be used for the applications.
The phase-locked multichannel Nd:YAG laser systems with the long- and short-range coupling via the
holographic gain gratings in the active elements are developed. The phase locking of various lamp- and diodepumped
loop Nd:YAG lasers with an interference contrast of the laser channels of up to 0.87 and a singlemode
lasing efficiency of up to 20% is experimentally demonstrated. The experimental results for the twoand
three-channel laser systems are generalized on multichannel laser systems using the numerical simulation.
It is demonstrated that the maximum number of the short-range-coupled laser channels can be increased
owing to the leveling of the parameters of laser channels to a value that is greater than that the maximum
number of the channels in the presence of the long-range coupling, which is limited by the damage threshold
of the active element of the interchannel coupling. Use of the multi-loop configuration of the laser resonator
allows compensating not only phase distortions but also a gradient of gain in the diode side-pumped active
elements.
The goal of this work was to design and investigate a gain switched, at room temperature lasing Fe:ZnSe laser. The active medium was a bulk, by Bridgman-technique grown Fe:ZnSe sample with the thickness 3.4 mm. The pumping was provided by electro-optically Q-switched Er:YAG laser with the oscillation wavelength 2.937 μm matching the local maximum of the Fe:ZnSe absorption. The Er:YAG Q-switched operation was obtained by the Brewster angle cut LiNbO3 Pockels cell placed between the rear mirror and the laser active medium. No additional intracavity polarizers were used. The maximum pumping pulse energy and length was 15 mJ, and ~300 ns, respectively. This pulse-length is close to room-temperature measured lifetime of Fe2+ ions in Fe:ZnSe crystal.
The pump radiation was directed into the Fe:ZnSe crystal which was placed inside the cavity formed by dichroic
pumping mirror (THR=92% at 2.94 μm and RHR~100% for 3.5-5.2 μm) and optimal output coupler with the reflectance ROC=90% at 4.5 μm, radius of curvature r = -200 mm. The maximum obtained output Fe:ZnSe laser energy was 1.2 mJ, the generated output pulse duration on the wavelength 4.5 μm was 65 ns (FWHM). The output pulse profile was approximately Gaussian. The crystal showed rather high uniformity of oscillation properties throughout its volume. For the case of tuning the CaF2 prism was implemented into the resonator. The tuning curve of generated Fe:ZnSe laser radiation covered the spectral range 3.9 - 4.7 μm.
Cr:ZnSe laser coherently longitudinally pumped with Tm:YAP microchip laser was realised.
The pumping laser consisted of Tm:YAP crystal (3x3 mm) with resonator mirrors deposited
directly on its faces (on rear face the dielectric layer with high reflectance for 1998 nm
wavelength and high transmittance for 790 nm pumping radiation wavelength; on output face
the dielectric layer with reflectance 97% at 1998 nm wavelength). The maximal output power
was 5.5 W and the generated radiation wavelength was 1998 nm. The main advantage of this
pumping was stable and still output without relaxation spikes (non-spiking).
The Tm:YAP laser radiation was collimated and focused by the set of two CaF2 lenses. The
pumping beam spot diameter inside the Cr:ZnSe crystal was 300 μm. The Cr:ZnSe laser
resonator consisted of flat rear mirror (HT at 1998 nm and HR at 2100 - 2900 nm) and curved
output coupler (r = -150 mm, R = 95% at 2100 - 2700 nm). The maximal output energy of
stable radiation was 4 mJ (pulse duration 10 ms, repetition rate 10 Hz). For wavelength tuning
the Lyott filter (quartz plate under Brewster angle) was placed between the Cr:ZnSe crystal
and output coupler. The generated radiation wavelength was continuously tunable from 2246
- 2650 nm.
The lead thiogallate (Dy:PbGa2S4) crystal doped with trivalent dysprosium ions was used as a laser active medium for
obtaining radiation in mid-IR spectral region. To prove in-band pumping, the Er:YAP laser generating 1.66 μm radiation
was used. This radiation was focused by CaF2 lens (f = 100 mm) on the investigated Dy:PbGa2S4 crystal placed inside
the resonator formed by an in-coupling flat-dichroic mirror with low reflectivity at pumping wavelength and with high
reflectivity within the 4-5 μm spectral range, and by an out-coupling concave mirror (500 mm curvature) with
reflectances of 86%, 88%, 89%, and 93% at 4325 nm. Three Dy:PbGa2S4 active crystals were investigated. The
Dy:PbGa2S4 laser was working at room temperature without any cooling. The maximal reached output energy was as
high as 275 μJ for the optimal mirror reflectance and the best Dy:PbGa2S4 crystal. The incident pumping energy was 132
mJ. The measured output radiation wavelength was 4332 nm with the spectral width of 62 nm. From the point of
efficiency it was recognized that the in-band pumping directly into 6H11/2 level results in decrease of lasing threshold and
increase of slope efficiency.
Fe:ZnSe is one of the most promising materials capable of generating broadly tunable laser radiation in the wavelength
range from 3.5 to 5 μm. The aim of the work was to test laser properties of the Bridgman-method-grown Fe2+:ZnSe
crystal activated through the synthesis process as an active medium coherently pumped with the Q-switched Er:YAG
laser whose oscillation wavelength (2937 nm) corresponds to the maximum of the Fe2+:ZnSe absorption spectrum. The
Er:YAG laser generated giant pulses with the duration 160 - 200 ns and energy 20 - 30 mJ. The repetition-rate was set
to be 1 Hz. The oscillation properties, such as the pulse length, energy, and generated beam spatial structure, of the
Bridgman-method-grown Fe2+:ZnSe crystal used as an active medium of Fe2+:ZnSe laser operated at room temperature
were investigated. The maximal obtained output energy of room temperature Fe2+:ZnSe laser was 580 μJ for the
absorbed energy of 5.3 mJ which corresponds to slope efficiency of 38%. The generated pulse waveform was found to
follow that of the pump one.
Cr:ZnSe laser active material is one of the favourite possibility how to generate broadly tunable mid-infrared
laser radiation at room-temperature. The aim of this study was to demonstrate and analyze pulsed as well as
continuous-wave laser action in bulk Cr:ZnSe crystals grown by the floating-zone method or by the Bridgman
method. The absorption spectra of Cr:ZnSe were measured to be from 1500 to 2000 nm, therefore various lasers
were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser
(generated wavelength 1658 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm), and diodepumped
Tm:YAP laser (generated wavelength 1980 nm).
In the first case, the Cr:ZnSe crystal grown by the Bridgman method was investigated. In the second case, the
Cr:ZnSe crystal grown by the floating zone method was studied. In both cases, the homogeneity of the active
Cr:ZnSe crystals was found reasonable good. The emission spectrum was from 2000 up to 2800 nm. The
Cr:ZnSe laser generated radiation was broadly continuously tunable in the range from 2050 nm up to 2750 nm.
The generated radiation beam spatial structure was close to TEM00.
Stimulated Raman scattering (SRS) in BaWO4 crystal under 1.56 μm pumping was investigated. Several (up to
fourth) Stokes components were observed. Mid IR spectral range 2.75 µm and 3.7 μm radiation was obtained using
BaWO4 crystalline Raman shifter. Under 1.318 μm pumping 4.3 μm and 4.7 μm oscillations in low phonon
PbGa2S4:Dy3+ laser were obtained.
Broadly tunable mid-infrared laser sources operated at room-temperature are desired in many technological and
medical applications. The aim of the project was to design and construct broadly tunable powerful Cr:ZnSe laser.
The investigated Cr:ZnSe various shaped bulk crystals were grown by the Bridgman method or by the floating zone method. The absorption spectrum was measured to be from 1500 to 2000 nm and the emission spectrum was from 2100 to 2800 nm. Three different lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1660 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm) and diode-pumped Tm:YAP laser (generated wavelength 1980 nm). The constructed Cr:ZnSe laser operated in pulsed as well as in continuous-wave regime. In the first case the Cr:ZnSe crystal grown by the floating zone method was studied. The maximal output power in continuous-wave regime was 310 mW with the slope-efficiency 73% for the Tm:YAP laser pumping. In the second case the Cr:ZnSe prism grown by the Bridgman method which served simultaneously as laser active medium and intracavity dispersive element was investigated. For the Er:YAP laser pumping the maximal output energy was 20 mJ with the slope-efficiency 36%. The output radiation was tunable in the range from 2050 nm up to 2750 nm. For the Tm:YAP laser pumping the maximal output power in continuous-wave regime was 175 mW with the slope-efficiency 24%. The output radiation was tunable in the interval from 2220 nm up to 2680 nm. The generated radiation beam spatial structure was close to TEM00.
The goal of our research was the construction of the laser emitting short pulses with high peak power in "eye-safe" region around wavelength 1.5 μm. We use Raman self-conversion of giant pulses at wavelength 1.3 μm in Nd3+-doped Raman active crystal SrMoO4 (diameter 4.4 mm, length 42 mm). Fundamental laser wavelength was obtained using this advanced solid-state medium Nd3+:SrMoO4, lasing at 1378.1 nm, and pumped at wavelength 752nm by free-running alexandrite laser. High-peak power required for efficient Raman conversion was reached by Q-switching of the Nd3+:SrMoO4 laser by V:YAG solid-state saturable absorber (initial transmission 93% @ 1380 nm). Specially designed resonator mirrors were used to ensure proper feed-back for Raman laser. The resonator pump mirror was concave with 0.5m curvature and with high transmission at 752nm and high reflectivity in the range from 1250nm to 1580 nm; the reflectivity of the output coupler was 3% @ 1380nm and 25% @ 1570 nm. Both mirrors have reflectivity around 1 μm as small as possible to prevent lasing at other Nd3+ lines. With the described laser system, simultaneous generation of wavelengths 1378.1nm and 1569.8nm was obtained. The single pulse output energy 0.8mJ at 1569.8nm was reached. The length of the generated pulse at this wavelength was measured to be 8.7 ns (FWHM). These values correspond with the peak power of 92 kW in eye-safe region.
Use of the self-adaptive Nd:YAG laser with dynamically adjustable passive Q-switch allowed to drill high-aspect-ratio
holes deeper than 7 mm in steel, aluminium, Ni-based alloy, and ceramics Al2O3, AlN, SiC at the average drilling rate
exceeding 1 mm per laser pulse, which is close to the initial drilling rates.
Phase-locked lasing of a three-channel holographic laser system based on self-pumped phase-conjugate loop oscillators
is experimentally demonstrated in accordance with a transient numerical modeling. The Nd:YAG laser system had three
laser outputs as the self-Q-switched laser monopulses interfering with a fringe pattern visibility tending to unity.
Cr:ZnSe crystals grown by the Bridgeman technique from the melt in inert gas (argon) under pressure were
characterized and utilized as effective laser active material.
Large crystalline boules with a necessary concentration of Cr2+ ions 1019 cm-3, practically homogeneously distributed
throughout the crystal bulk (50 mm in diameter and up to 100 mm in length), were prepared. For the laser evaluation
the Cr:ZnSe samples in the form of 6 mm thick blocks were polished.
Cr:ZnSe laser was longitudinally coherently pumped either with flashlamp-pumped Er:YAP laser radiation (emission
wavelength 1658 nm) or with diode-pumped Tm:YAP laser radiation (emission wavelength 1980 nm).
In the first case, the Cr:ZnSe laser was pumped with radiation of Er:YAP laser working in free-running regime (pulse
length 200 &mgr;s, pulse energy 200 mJ, repetition rate 1 Hz). The maximal obtained Cr:ZnSe laser pulse energy was 14
mJ (slope-efficiency 73%). Using the dispersive prism inside the resonator, the output laser radiation was broadly
tunable from 2150 nm up to 2600 nm.
In the second case, the Cr:ZnSe laser was pumped with radiation of diode-pumped solid-state Tm:YAP laser working
in pulsed as well as continuous-wave regime, for which the maximal obtained Cr:ZnSe laser output power was 200
mW (slope-efficiency 67%). The output spectrum of generated radiation covered the range from 2100 nm to 2400
nm. The temporal profile and spatial structure of laser beam were measured.
The Cr:ZnSe crystal grown by the Bridgeman method was demonstrated as an efficient broadly tunable laser active
material generated radiation in the mid-infrared spectrum and operated in room-temperature.
Tunable mid-infrared laser radiation sources are of interest for many applications in spectroscopy, ranging,
remote-sensing, medical diagnosis and treatment and also for pumping nonlinear (OPO) and laser materials.
The ZnSe:Cr2+ is a promising laser active material for lasing in the range of 2-3 μm. Up to now number of
sources have been used for pumping ZnSe:Cr2+ active medium: Er-fibre laser, color-center laser, Co:MgF2
laser, Tm lasers, and Raman-shifted Nd:YAG laser [1-4].
In our study we have demonstrated, characterized and compared ZnSe:Cr2+ laser coherently pumped either
by flashlamp-pumped Er:YAP (wavelength 1.66 μm) or diode pumped Tm:YAP (wavelength 1.97 μm) laser
radiations.
For the case of ZnSe:Cr2+ laser pumping by wavelength 1.66 μm, the Er:YAP laser was constructed. From
the measured output radiation characteristics followed that the maximal ZnSe:Cr 2+ laser output pulse energy
was 5.5 mJ (slope efficiency 23%), and the length of pulse 120-160 μs. With the help of dispersive prism
inside the resonator, the generated laser radiation was tunable from 2100 nm to 2450 nm with only 2 times
drop in laser efficiency. The temporal profile and spatial structure of the generated laser beam were
measured.
Consequently, the diode-pumped Tm:YAP laser was constructed for coherently pumped ZnSe:Cr2+ laser.
LIMO laser diode (40 W) was used for longitudinal pumping of Tm:YAP laser. The output characteristics
and tuning curves were measured for various ZnSe:Cr2+ laser resonator arrangements and also for various
pumping radiation conditions in pulsed regime (pulse duration, repetition rate, duty cycle).
The maximal obtained ZnSe:Cr2+ laser output pulse energy was 0.35 mJ for the Tm:YAP pump pulse energy
13.5 mJ (pulse radiation 5 ms, repetition rate 20 Hz). The generated laser radiation was tunable from 2100
nm to 2450 nm. The temporal profile and spatial structure of the generated laser beam were measured.
The purpose of this work was to determine the relative efficiencies of new Nd3+-doped laser active/Raman - tungstate, molybdate, and fluoride - materials (SrWO4, PbWO4, BaWO4, SrMoO4, PbMoO4, SrF2, and LaF3) under selective longitudinal optical pumping by the alexandrite (~750nm), or diode (~800nm) laser. Crystals with various length, orientations and active ions concentrations were tested. To optimize the output of the tested lasers a set of input dichroic and output dielectric mirrors with different reflectivities were used. For realized lasers operating at pulsed free-running regime, threshold energy, slope efficiency, emission wavelength, and radiation polarization were determined. For each crystal, fluorescence lifetime and absorption coefficient under given pumping were established. The slope efficiency in case of Nd3+:PbMoO4 laser at wavelength 1054nm was measured to be 54.3% with total efficiency of 46% which is the best result obtained for all new tested crystals. For Nd3+ doped SrWO4, PbWO4, and BaWO4 crystals simultaneous laser and self-Raman emission were demonstrated in Q-switched regime. Thus newly proposed laser Raman crystals demonstrate high efficiency for Nd3+ laser oscillations comparable with well known and widely used Nd:KGW crystal. Further improvement in the quality of tungstate and molybdate type crystals should result in further increase in lasing efficiency at 1.06μm wavelength. Self Raman frequency conversion of Nd3+-laser oscillations in these crystals should result in high efficient pulse shortening, high peak power and new wavelengths in 1.2-1.5μm wavelength region.
Raman, spectroscopic and laser investigation of new multifunctional Nd3+:SrWO4 laser active and Raman crystal are presented. Efficient intracavity stimulated Raman scattering in Nd3+:SrWO4 laser was obtained at 1.16 μm.
Properties of the laser operation and simultaneously stimulated Raman scattering in the new SRS-active neodymium doped SrWO4 crystal coherently end-pumped by alexandrite 752 nm laser radiation were investigated. The maximum generated energy 90 mJ from the free-running Nd3+:SrWO4 laser at 1057 nm wavelength was obtained with the output coupler reflectivity 52%. The slope efficiency reached s = 0.52, the beam characteristic parameters M2 and divergence q were 2.5 ± 0.1, and 1.5 ± 0.1 mrad, respectively.
Maximal output energy of 1.46 mJ for the fundamental wavelength was obtained for Q-switched Nd3+:SrWO4 oscillator with a double Fabry-Perrot as the output coupler (R = 48%), and with the 5% initial transmission of LiF:F2- saturable absorber. Up to 0.74 mJ energy was registered at the first Stokes frequency. The pulse duration was 5 ns and 2.4 ns for the fundamental and Stokes radiation, respectively. The energy of 1.25 mJ at 1170 nm was obtained for closed Raman resonator with special mirrors.
For the case of mode-locking, two dye saturable absorbers (ML51 dye in dichlorethan and 3955 dye in ethanol) were used and SRS radiation in the form of pulse train was observed. The influence of the various Raman laser output couplers reflectivity as well as the initial transmissions of passive absorbers were investigated with the goal of the output energy maximization at the Stokes wavelength. In the output, the total measured energy was 1.8 mJ (for ML51 dye) and 2.4 mJ (for 3955 dye). The SRS output at 1170 nm was approximately 20% of total energy.
Stimulated Raman scattering in BaWO4 crystal under high-energy pumping of a self-phase-conjugated LiF:F2- Q-switched Nd:GGG laser is investigated. The output Stokes radiation obtained has the pulse train energy of up to 2 J, the peak power of up to 1 MW, and the conversion efficiency of up to 20%.
A laser scheme for phase locking of radiation of two self-phase-conjugated Nd:YAG lasers by coupling in active rod gain gratings is proposed, theoretically studied, and experimentally tested. A single-mode, single-frequency radiation of the proposed system has the peak power equal to 15 MW, which exceeds the summed peak power of two initial lasers. (Summary only available)
A CW pumped Nd:YAG laser with combined Q-switching by an active Q-switch based on a radially variable Fabry-Perot interferometer and a passive Q-switch on a LiF:F2- crystal, is submitted. The conditions for a matched cavity dumping are achieved. (Summary only available)
This paper is focused on a design of flexible laser systems capable to provide spatial transformation of the pump radiation into the spectral domain of the output laser oscillation using specially designed “spatially dispersive” laser cavity. These systems also provide ultrabroadband or controlled spectral linewidth of the output laser oscillation. The theoretical analysis based on gaussian approximation for the designed laser cavities with “spatial dispersion” was used to provide maximum spatial resolution of the spatial-spectral transformation. The transformations of the spatial distribution of the pump radiation into the spectral domain of the output laser oscillation were experimentally demonstrated in the gain-switched LiF:F2+** and LiF:F2- lasers with total efficiencies of up to 20% and output pulse spectrum width wider than 140 nm, centered at 0.96 μm and 1.14 μm, correspondingly. As a result of the optimization of the angular dispersion of the output radiation, the simultaneous phase-matching for second harmonic generation in the single nonlinear crystal was realized for the whole oscillation spectral range. This technique allows to use a nonlinear frequency conversion for nonlinear transformation of the beam spatial distribution. Due to this, the ultra broadband (>100 nm) or multiline (20 lines) second harmonic and sum frequency oscillations were demonstrated in a LiIO3 nonlinear crystal with an overall efficiencies of up to 12%.
New Nd:SrWO4 and SrMoO4 crystals (45 mm and 33 mm of legnth, respectively) were investigated as Raman frequency converters of 50 picosecond Nd:YAG pulses and compared with already previously measured BaWO4 and KGd(WO4)2(KGW) tungstate crystals (33 mm and 40 mm of length, respectively). A forward SRS action was achieved in both new crystals. During the experiment the threshold energy of stimulated Raman process, generated wavelengths, and conversion efficiencies were measured. Single-pass first Stokes conversion efficiencies reached 25% and 21% for Nd:SrWO4 and SrMoO4 crystals, respectively. These values were compared with the maximal first Stokes efficiencies of previously studied crystals measured in the same experimental setup yielding: BaWO4 (η = 25% and KGW (η = 22%). As concerned the threshold - it was comparable for BaWO4, Nd:SrWO4, and SrMoO4. The SRS effect in KGW crystal started for ~25% higher pump energy. Our study shows that new Nd:SrWO4 and SrMoO4 crystals are other promising materials for picosecond Raman generation.
We present a novel technical approach to build a multiwavelength/superbroadband laser source based on a combination of spectral and spatial domains. This approach provides a direct transformation of spatial domain of the pumping beam into spectral domain of the output oscillation. Several spatially dispersive laser cavities were designed and studied both theoretically and experimentally for optimal spatial to spectral transformation. This spatial to spectral transformation was demonstrated for LiF:F2+** color center laser, single broad-stripe diode laser operating at 660nm and 1560 nm multi-stripe diode laser.
The mathematical model of the optically pumped molecular laser has been built. The satisfactory fit of the computer simulation results with the experimental data has been established. The optimization of the CO laser with the optical pumping in (2,0) overtone was carried out by the numerical modeling methods.
The detailed site-selective and time-resolved fluorescence laser spectroscopy and kinetic measurements with high spectral and nanosecond temporal resolution were applied to analyze the M and N absorption bands at the 4I9/2(1) yields 4G5/2(1) crystal field (CF) transition in the CaF2:Nd3+ crystal at 4.2 K. It was found that at helium temperatures the dynamically split spectral line at the 4I9/2(1) yields 4G5/2(1) CF transition of coherently coupled Nd3+ ions in the pair M- and quartet N-centers is inhomogeneously broadened. Small variation of fluorescence lifetimes of the 4F3/2 and 4D3/2 levels due to small variation of distances between Nd3+ ions in the pairs was found. Approximately 1 percent variation of the Nd-Nd distance in the pair -center was determined form lifetime variation of the 4F3/2 manifold.
An opportunity to compensate phase and polarizing distortions of the laser radiation directly in Nd:GGG active medium and also in phototropic LiF:F2- crystal is investigated. We found that an application of modified Sagnac interferometer with passive LiF:F2- Q- switcher, located inside it, allows not only to increase stability and power of laser pulses, but also to narrow the laser oscillation spectrum. The possibility is demonstrated of generating single-mode radiation with an energy in a train of laser pulses higher than 7 J, a peak power of a single pulse in a train up to 50 kW, the spatial brightness exceeding 5 x 1010 W/cm2 x sr, and the coherence length in excess of 13 m.
Detailed study of Stimulated Raman scattering (SRS) of 1.06- micrometers , 50-ps pulses in BaWO4 and KGW crystals was performed. Single-pass, double-pass and Raman cavity arrangements were compared regarding threshold intensity, conversion efficiency and pulse structure. Single-pass conversion efficiencies reached 25 percent for both BaWO4 and KGW. Double passing of the pump beam slightly improved the efficiency to 35 percent. Placing the BaWO4 crystal into a cavity and optimizing the performance by varying the output coupler spectral characteristics and the resonator length, 55 percent pump-to-first-Stokes efficiency has been obtained. The maximum of the Raman laser output energy was 3 mJ. The output consisted of 2-4 picosecond pulses at the 1180 nm wavelength. Dependence of the BaWO4 Raman laser output beam structure on the pumping energy was studied. The concentric ring profile, typical for transient SRS, was homogenized using a cyclic olefin polymer coated silver hollow glass waveguide. A similar study was performed with KGW crystal, for which the first Stokes wavelengths are 1159 nm or 1177 nm, depending on the sample orientation. Due to lower gain value, Raman laser energy reached 2 mJ and maximum efficiency was 30 percent. Based on our comparative study, a new BaWO4 crystal is highly suitable for utilization in the near IR picosecond Raman lasers.
A novel technical approach to build a multiwavelength laser source for DWDM applications is described. The basic idea of this system is to maintain simultaneous lasing operation in a gain medium at different wavelengths without mode competition. The system uses a novel dispersive cavity. By designing this cavity structure appropriately, the system creates its own microcavities-channels each lasing independently at different wavelengths across the complete gain spectrum of the laser active material. Multifrequency lasing on the basis of a single diode laser chip was analyzed theoretically and demonstrated experimentally.
BaWO4 and KGd(WO4)2 (KGW) tungstate crystals (33 mm and 40 mm of length, respectively) were investigated as Raman frequency converters of picosecond and nanosecond second-harmonic Nd:YAG pulses. During the experiment the threshold energy of stimulated Raman (SR) process, generated wavelengths, and energy for nanosecond and picosecond pump pulses with both nonlinear crystals were measured. For BaWO4 crystal, the threshold pumping intensity was measured to be 530 MW/cm2 for psec pumping and 200 MW/cm2 for nsec temporal region. The corresponding Raman gain values were 14.3 cm/GW (picosecond pump) and 38 cm/GW (nanosecond gain). For KGW crystal the threshold intensity values 530 MW/cm2 for psec and 340 MW/cm2 for nsec were measured with corresponding Raman gain values of 11.8 cm/GW (psec) and 18.6 cm/GW (nsec). The Stokes components up to the third order in both psec and nsec regions were detected. Temporal length measurements of pump and Stokes pulses in both crystals revealed pulse shortening by a factor of approximately 2 during the SR process. Due to a high value of Raman gain of a new BaWO4 crystal under both nsec and psec pumping, this crystal can be considered as a unique candidate for utilization in solid-state Raman laser systems.
The powerful neodymium lasers with the self-phase-conjugation (SPC) and passive Q-swither are submitted. It is shown, that the application of a LiF:F2- crystal as Q-swither and SPC-mirror simultaneously, and also a Sagnac interferometer as end reflector of the cavity allows to increase efficiency and quality SPC-radiation. High power and spatial laser characteristics are obtained: Nd:YAG laser -- 114 W average power at 0.5 mrad beam divergence; Nd:YAP laser -- 51 W average power at 1.2 mrad beam divergence; Nd:Glass laser -- 18 J in pulse train at 1 mrad beam divergence.
The laser systems with passive Q-switching by LiF:F2 crystals for precision technology are submitted. It is shown, that the application of laser system of the combined radiation allow to increase the processing productivity, and laser systems with the combined Q-switching-the processing quality.
Self-pumped phase-conjugate multiloop Nd:YAG, Nd:YAP, and Nd:Glass lasers are investigated and developed. The parametric feedback is realized by dynamic holographic gratings in active and passive LiF:F2- Q-switcher medium. High power and spatial laser characteristics are obtained: Nd:YAG laser - - 114 W average power at 0.5 mrad beam divergence; Nd:YAP laser -- 51 W average power at 1.2 mrad beam divergence; Nd:Glass laser --18 J in pulse train at 1 mrad beam divergence.
Stimulated Raman scattering of picosecond pulses was investigated in KGd(WO4)2, and BaWO4 tungstate crystals. BaWO4 crystal was previously found to be a new very efficient material for pumping with nanosecond pulses. In our experiment, we used the second harmonic output of a mode-locked Nd:YAG laser system, which generated single pulses of 28 ps duration. The length of the crystal was 40 mm for KGW, 23 mm for KYW and 29 mm for BaWO4. The SRS threshold, conversion efficiency, and time dependence of the first Stokes with picosecond resolution were measured. Picosecond Raman gains at a 532 nm wavelength were found to be correspondingly 11.5, 18.7, and 14.4 cm/GW for KGW, KYW, and BaWO4. The Raman shifting up to the third Stokes component was detected, and the first Stokes conversion efficiency reached 30 percent in BaWO4 and 18 percent in KGd(WO4)2. Measurements of a temporal pulse length have shown that the first Stokes pulse was twice shorter than the pump pulse. The new BaWO4 crystal occurs to be an efficient solid state Raman material for a wide variety of pump pulse durations.
Optimization and adaptation of 15 - 200 micrometer small dia and 2 - 20 mm deep holes drilling with the hole shape variation less than plus or minus 10% are discussed. For this purpose, the single-frequency laser system with self-phase- conjugation and passive Q-switching by a scanned gradiently colored LiF:F2- crystal is used. Steels, hard- facing and aluminum alloys, and ceramics are used as samples.
Sergey Mirov, Robert Pitt, Alex Dergachev, Wonwoo Lee, Dmitri Martyshkin, Olga Mirov, Jeremy Randolph, Lawrence DeLucas, Christie Brouillette, Tasoltan Basiev, Yurii Orlovskii, Olimkhon Alimov, Ivan Vorob'ev
A novel experimental set-up using laser-induced breakdown spectroscopy (LIBS) for environmental analyses of heavy metals is described in this paper. It is based on state-of-the-art spectroscopic equipment, advanced detectors, and laser atomizers: a 0.75 m spectrometer ARC-750, intensified TE- cooled 256 X 1024 CCD camera, probe with fiber optic guide for signal transportation, and Nd:YAG laser plasma atomizers with two different methods for sample delivery. In the first method the liquid solution containing the atoms to be investigated is drawn into the chamber of the nebulizer. The mixture passes through the nozzle, accompanied by argon gas along with formed aerosol, and enters the plasma plume, which is generated by the laser spark in argon. The second method is based on direct generating of the plasma in the water jet of a continuously circulating sample. LIBS testing of samples containing Al, Cd, Cu, Fe, Pb, Zn, and Cr ions was compared with results using atomic absorption spectrophotometry. Initial indications showed good agreement between these two methods. Detection levels of less than 100 ppb were observed for copper and chromium. The described spectroscopic system exhibits high sensitivity, accumulation of luminescence spectrum in real time; and high dynamic range for concentrations detection from 100 ppb to 1000 ppm.
Several years after the discovery of Raman scattering of light, solid state Raman lasers are beginning to reach the stage of commercial applications. This talk will review the basic concepts of Raman gain with a special emphasis on Raman laser crystals. Examples of spectroscopic properties of important materials are presented. The use of these materials in shared-, coupled,- and external-resonator Raman laser systems is described. Design parameters affecting efficiency, beam quality, and temporal pulse width are discussed. Examples will be presented of the use of these lasers for transmitters in atmospheric lidar, marine imaging lidar, adaptive optics guide-stars, and materials processing applications.
All solid state (SS) laser induced fluorescence (LIF) spectrometer based on tunable LiF:F2- color center (C.C.) MALSAN laser with second and fourth harmonic generation was optimized for trace metallic concentration measurements in water solutions. Two types of heavy metals atoms Sn and Pb were analyzed using inexpensive low temperature types of the propane/butane-air flames. The maximum sensitivity of 10 and 50 ppb with good linearity of fluorescence intensity concentration dependence was obtained for Sn and Pb atoms, respectively, using a monochromator for the fluorescence wavelength selection. When the monochromator was replaced by a set of color optical filters the sensitivity of 0.3 ppb for Pb atoms was obtained. Hence, the sensitivity was increased more than 150 times for more cheap and simple registration set-up. An attempt was made to use more compact super- broadband LiF:F2- C.C. laser to replace the MALSAN laser in LIF spectrometer. Up to now the sensitivity of 1 ppm for Pb with the monochromator based fluorescence registration system was obtained in the latter case.
The repetitively pulsed Nd:YAG laser with dynamic cavity formed with participation of dynamic holographic gratings induced in Nd:YAG laser crystal and Li:F absorber has been investigated. The generation regimes and technological opportunities of this Nd:YAG laser were studied. High spatial brightness of radiation at diffraction limited divergence has allowed to carry out effective punching of calibrate holes in different materials with a diameter up to 15 micrometers and maximal depth up to 20 mm.
Q-switched regimes of the nanosecond pulse-periodic Nd:YAG laser with dynamic cavity formed with participation of dynamics holographic gratings in laser elements have been investigated. A Sagnac interferometer was applied as a laser cavity mirror for angular selection of initial radiation. As a passive Q-switch, we used saturable absorber crystal LiF:F2-, which increased total intracavity diffraction efficiency of dynamic gratings completing the cavity. Self-pumped phase conjugation in Nd:YAG amplifier and LiF:F2- absorber provided adaptive properties of the cavity. The peak power of generated beam with diffraction quality exceeded 17.5 MW and the average power achieved 50 W.
The peculiarities of energy levels structure of laser-active F3+ color centers in LiF crystals were studied. The dependencies of polarization and fluorescence intensity of LiF crystals with F3+ centers against polarization of powerful laser irradiation which originates two-photon excitation of F3+ centers, were measured and calculated. It was shown that the two-photon transition leads to the excitation of unknown previously spin-singlet electronic state, possessing 1A1 wavefunction symmetry.
The theoretical and experimental investigations of temporal dynamic of LiF:F2- color center laser oscillation are presented. It was found that due to the high amplification cross section, the lasing temporally overlaps with the pump pulse. The peculiarities of LiF:F2- lasing under various pump sources are under consideration.
The analysis of simultaneous second and fourth harmonic generation of superbroadband LiF:F2- color center laser radiation in different nonlinear crystals is presented. The experiments have shown high laser and harmonic conversion efficiencies. Simultaneous generation of continuous spectra in near IR, visible and Uv spectral regions, and multiline oscillation with high spectral resolution (Delta) v < 5 cm-1 have been obtained.
New spin-triplet electronic states of laser-active F3+ color centers in LiF crystals are discovered. The triplet-triplet absorption spectra from low laying 3E state to the high laying states, triplet-triplet 3T(alpha ) yields 3E fluorescence spectrum and 3E yields 1A1 triplet-singlet phosphorescence spectrum are measured. Temperature dependencies of nonradiative singlet-triplet 1E yields 3E and triplet- singlet 3E yields 1A1 transitions probability are found. The influence of spin-triplet states on the LiF:F3+ color center laser characteristics is discussed. The new way of obtaining of tunable oscillation in wide visible range using triplet-triplet transition is offered.
Tasoltan Basiev, Vladimir Fedorov, Alexander Karasik, S. Lin'kov, Yurii Orlovskii, Vyacheslav Osiko, Vitaly Panov, Alexander Prokhorov, Ivan Vorob'ev, Peter Zverev
Solid state (SS) tunable LiF:F2 color center laser with second and fourth harmonic generation for visible and ultra violet spectral ranges was developed for the laser induced fluorescence spectroscopy (LIFS). The construction and properties of excitation, registration and flame atomization systems for water solution diagnostic are discussed. The testing experiment with low iron concentrated water sample exhibits ultrahigh sensitivity which was estimated to be 0.05 ppb in our set-up. The SS LIFS spectrometer developed is usable to measure more than 42 metal elements in solution on the ppm, ppb level for various medical and biological applications.
The irreversible bleaching of F2⁻ color centers (CC) in a LiF crystal under influence of powerful IR radiation with wavelength 1.06 μm has been observed earlier [1]. It has been shown that F2⁻ CC bleaching is due to two-photon absorption from the excited state and results in the formation of a stable dichroic spatial band in the crystal. It has been shown [2-4] that F2⁻ CC irreversible bleaching is the reason of both spectral and polarisation "collapses" in Nd lasers with LiF:F2⁻ crystals as passive Q-switches.
This paper is devoted to the donor (chromium ion) excitation-energy decay caused by interaction with the acceptors (rare earth ions) in garnet crystals, as analyzed within the approximation of a static nonradiative energy transfer.
We report here on a novel Color Center Laser (CCL) optical construction, providing two unique regimes of generation: (a) a simultaneous generation across the whole emission region of the LiF:F2- active medium (1.1-1.24 micrometers ) with efficiency of 15% and a simultaneous frequency doubling in the visible green-red spectral region (0.55-0.62 micrometers ); (b) a regime of multi frequency lasing with a special preassigned spectral distribution or spectral coding by means of placing a special mask or image controller into the pump beam.
Barium nitrate Raman laser pumped with nanosecond YAG:Nd laser is investigated. High energy conversion efficiencies to the first, second, and third Stokes components up to 60%, 35%, and 25%, respectively, are obtained. Results on development of Raman laser for the eye safe spectral region are presented.
Passive Q-switching of 1.3 micrometers neodymium lasers with Nd2+:SrF2 and V3+:YAG crystalline saturable absorbers are studied. Giant pulses up to 5 mJ energy and 40 ns duration were obtained. Efficient Raman shifting of the 1.3 micrometers pulses of passively Q-switched lasers to 1.55 micrometers wavelength are realized in Ba(NO3)2 crystal.
For a number of neodymium doped fluoride crystals both with regular and disordered structure the Judd-Ofelt analysis of absorption spectra have been performed, and fluorescence and lasing spectra were studied in order to reveal the most promising materials for optical amplification in a 1.3 micrometers telecommunication window. The most suitable crystalline media investigated was found to be cubic disordered fluorides based on (50 - 70%) SrF2 - (50 - 30%) CaF2 solid solutions with Nd3+ optical centers having tetragonal local symmetry. These crystals have (1) low value of excited state absorption line strength, (2) high metastable level lifetime (1.2 - 1.3 ms), (3) high enough emission cross section for fluorescence (approximately 4 X 10-21 cm2), and (4) proper fluorescence peak at about 1310 nm wavelength and comparatively wide fluorescence band with about 20 nm FWHM.
It is well known that Neodymium glasses are widely used as active media in powerful picosecond laser systems. However, low thermal conductivity of glasses with broad bands of absorption and luminescence limits their use in pulsed lasers with high repetition rate. At the same time, disordered crystals having broad inhomogeneous bands of active ions and combining properties of both glasses and crystals may be reckoned as active media for ultrashort pulse lasers with high repetition rate. It has been shown recently that Calcium-Niobium-Gallium disordered garnet crystals doped with Nd3+ ions (CNGG:Nd3+) with broad inhomogeneous spectrum of amplification are prospective active media for the laser generation of powerful ultrashort pulses1 . In ref. 1 a passively mode-locked (PML) with a saturable dye absorber CNGG:Nd3+ laser generated trains of 7 ps pulses at a repetition rate of 0.3 Hz. To eliminate a liquid absorber and get an all solid state laser configuration one can mode-lock a laser actively with a crystalline modulator. But while the active mode-locking (AHL) technique may lead to the generation of high stable and reproducible laser pulses with a high repetition rate, its main drawback in comparison with the PML is relatively large pulse duration, in particular, at lamp pumping. Nevertheless, the use of a highly efficient LiNb03 acousto-optic modulator (AOMJ 2 •3 in a glass laser has led to the generation of pulses with duration of 13 ps 4 , so the operation of a laser on disordered crystals doped with Nd 3+ ions actively mode-locked with the AOM is a matter of considerable interest. It is known also that LiF crystals with F 2 color centers are successfully employed for passive Q-switching6 and the application of these crystals as passive Qswitchers to AHL lasers may give sufficient rise to pulse peak power. The aim of this work is to investigate the operation of actively mode-locked with LiNb03 AOM laser on a Calcium-Lithium-Niobium-Gallium disordered garnet crystal doped with Nd3+ ions (CLNGG:Nd3+) and a LiF:F2 passive Q-switch.
The Czochralski crystal growth of pure Cr, Er and Ho doped as well as Cr,Er and Cr,Ho codoped yttrium silicate Y2SiO5 (YSO) is reported. The growth conditions for producing the inclusion free single crystals of high optical quality are discussed. Spectroscopic properties of the singly doped and codoped material at room temperature are compared. Energy transfer processes from Cr4+ ions to Ho3+ and Er3+ ions in YSO host have been demonstrated for the first time.
We present the results of investigations of nonlinear absorption in alkaline-earth fluoride crystals containing divalent neodymium ions, and also the results of utilizing these crystals for passive Q-switching and mode-locking in solid state lasers radiating in the wavelength range (1.3 - 1.6) micrometers . Spectroscopic parameters of the studied materials such as the effective absorption cross-section and the relaxation time of the state of self-induced transparency (SIT) were estimated. The nature of the residual absorption was determined in these crystals and a simple spectroscopic model describing the SIT process in MeF2:Nd2+-crystals is offered. It is demonstrated that MeF2:Nd2+-crystals can be used as Q- switches for the lasers of the near IR wavelength range. The results of Q-switching of neodymium and erbium lasers generating in the ranges of 1.3 and 1.54 micrometers , respectively, are presented. The single-peak generation regime and generation of a train of modulated pulses are investigated. The use of SrF2:Nd2+-crystals allowed us to realize the mode-locked regime in YAG:Nd-crystal laser, operating on the transition 4F3/2 yields 4I13/2. Evaluation of the duration of peaks gives the time less than 400 psec.
The results are presented of theoretical and experimental studies of two-step photoionization and photochemistry of color centers in LiF crystals. The exact analytic expressions were obtained for the population of optic centers energy levels in the process of two-step photoionization within a framework of kinetic equations in three-level approximation. A transfer from cw to pulsed-periodic excitation was analyzed. An analytic dependence was obtained of the ionization cross-section on the incident light flux intensity. For the first time the cross-section was estimated of the photoionization from the excited level of F2 color center in LiF crystal being pumped by 532 nm wavelength radiation. The processes were detected of mutual phototransformations of F3, F3+ and N color centers in oxygen-free LiF crystals. It was demonstrated that the presence of F3 and F3+ color centers in crystals is necessary for selective accumulation of N color centers at high temperature (300 K) action of Nd:YAG laser third harmonic radiation. In LiF- OH crystals the processes of mutual phototransformations were detected in a CC ensemble with absorption bands maxima at wavelengths 380 nm, 450 nm, and within the range 500 - 570 nm. It was demonstrated that an effective destruction of the CC absorption band (380 nm) along with the formation of absorption bands with maxima within 500 - 570 nm takes place under high-temperature (300 K) action of Nd:YAG laser third harmonic radiation ((lambda) equals 354 nm). Reverse phototransformation with the recovery of the band at 380 nm takes place along with the known phototransformation F2 (450 nm) yields F2+ (654 nm) under the subsequent action of the same laser second harmonic radiation ((lambda) equals 532 nm).
A new class of high power solid state lasers on neodymium containing media with passive Q- switches on LiF:F2- crystals was investigated. The generation regimes and the technological possibilities of such lasers were studied.
Results of spectroscopic and radiation investigations of disordered calcium-niobium-gallium garnets (CNGG) with wide inhomogeneously broadened lines in absorption and luminescence of Nd3+ are presented. A method of a selective and frequency tuned laser excitation at T equals 77 K provided discovery of four groups of optical centers and development of Stark multiplet 4F3/1 and 4I9/2 levels schemes for these centers. Laser excitation at the 4I11/2 yields 4F3/2 transition at T equals 300 K during time resolved luminescence spectra recording at the same transition resulted in discovery of an inhomogeneous character of amplification spectrum broadening as well as in estimation of spectral energy migration among the centers. This time it was found to be longer than the 4F3/2 level lifetime (150 microsecond(s) ec). Results of the investigation of free-generation and passive mode-locking regimes in lasers based on disordered garnets with neodymium are presented. It is shown that energy parameters of the lasers based on CNGG are higher than those of glass lasers. In the passive mode-locked regime pulses are generated with (lambda) equals 1.06 micrometers and duration time 5 - 7 psec. The pulses have positive linear frequency chirp and spectrum broadening up to 60 cm-1. Compression of the chirped pulses in an external compressor provides transfer to femtosecond time scale.
A detailed experiment on phase conjugation via degenerate four-wave mixing in LiF:F2- and NaF (F2+)* crystals pumped by pulse-periodic Nd:YAG laser is described. The dependence of the efficiency of phaser conjugation on the energies and polarizations of the interacting beams and on the concentration of F2- CC is described. The mechanism of phase conjugation is connected with the saturation of the absorption in the color center crystals. Phase conjugation was investigated in LiF:F2- crystals that worked simultaneously as a passive Q-switch of a Nd:YAG laser. This allows use of the LiF:F2- crystal as a phase conjugated mirror of a Nd:YAG laser.
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