Ceramic materials are interesting alternative to single crystals for various optoelectronic applications including high-power
lasers and phosphors. Main advantages of ceramics compared to their single crystal counterparts are lower costs
of production, ability to incorporate higher dopant concentrations and possibility to manufacture larger elements. In the
present work, the spectroscopic properties of ceramics obtained by two different methods are compared. First method
relies on solid-state reaction of nanometric oxide powders, i.e. Al2O3, Y2O3 and Nd2O3. The oxides with addition of
tetraethyl orthosilicate were sintered under vacuum and anealled. Second method is the synthesis of neodymium-doped
aluminium garnet (Nd:YAG) nanocrystalline powders prepared by coprecipitation technique. The powders were calcined
and vacuum-sintered in optimized process conditions. For all ceramic samples fluoresce and decay data is presented.
Presented results indicate that the ceramic samples obtained by reactive sintering method have superior spectroscopic
properties compared to the samples synthesized from Nd:YAG nanocrystalline powders. The optimization of
manufacturing process allowed to demonstrate ceramics having the properties comparable to single crystal counterparts.
Optical quality and luminescent properties make the ceramics manufactured at the Institute of Electronic Materials
Technology an interesting candidate for laser applications.
The Nd:YAG ceramics of nominal 1% and 2% Nd dopant were produced by a solid-state reaction of high-purity (4N)
nanometric oxides powders i.e. Al2O3, Y2O3 and Nd2O3. Yttrium oxide nanopowder (XRD crystallite size of 79 nm) was
produced by precipitation from water solution of high-purity hydrated nitrate, by means of ammonia hydro-carbonate. The
cold isostatic pressing method was applied to densify granulated powder. Further the sintering and annealing processes were
deployed to produce the final Nd:YAG ceramic samples. Mean grain sizes of about 20 µm and grain boundaries less than
10 nm of elaborated Nd:YAG ceramic samples were evaluated in SEM and TEM measurements. Thus, in microscale the
quality of obtained ceramic was quite satisfactory. However, in macroscale, the samples had unacceptable level of voids and
pores observed in visual inspection, which resulted in low 76% transmission, corresponding to extinction coefficient of
0.32 cm-1 at 1064-nm wavelength. The sizes of defects, pores and inclusions were of several dozens of micrometer. The
active elements of rod and slab shape were fabricated and characterized in two diode pumping laser set ups. In end pumping
configuration as a pump source 20-W fiber coupled laser diode was deployed. For the low duty cycle pumping (1 ms/20 Hz)
above 30% slope efficiency was achieved. In the best case, 3.7 W of output power for 18 W of pump power, with M2 <1.4
were demonstrated for uncoated ceramics rod of φ4x3mm size. We have used uncoated elements, thus we can expect
increase in laser parameters for optimized pumping conditions and samples with anti-reflective coatings. The parameters of
elaborated ceramic material at this stage of work are unsatisfactory for laser application. However, the results of TEM
measurements and laser characterizations seems to be quite promising..
We report on the first, promising production of Nd:YAG ceramics made in Poland. The Nd:YAG ceramics was produced
by a solid-state reaction of high-purity (4N) nanometric oxides powders i.e. Al2O3, Y2O3 and Nd2O3. After sintering
process mean grain sizes of 2%Nd:YAG samples were about 20 μm and transparency of its were comparable to
0.9% Nd:YAG single crystal. Two types of active elements: rods and slabs were fabricated and characterized in several
diode pumping schemes. In end pumping configuration as a pump source 20-W fiber coupled laser diode operating in
low duty cycle regime (1 ms pump duration /20 Hz) was deployed. In the best case, 3.7 W of output power for 18 W of
absorbed pump power, M2 <1.4 were demonstrated for uncoated ceramics Nd:YAG rod of φ4x3mm size in preliminary
experiments. For the ceramics of two times lower Nd dopant level above 30% slope efficiency was achieved. In case of
slab ceramic side pumped by 600-W laser diode stack above 12 W was demonstrated with slope efficiency of 3.5%.
Characterization of diode pumped Er:YVO4 microchip laser working in an "eye-safe" spectral region is done. Two
active materials for microchip laser based on Er:YVO4 and Er:YVO4 + CaO crystals were investigated. The dimension
of the microchips was in both cases the same: an aperture 8.3 x 10.4 mm and thickness 2.9 mm. The concentration of
active ions Er3+ was 0.5 at% in both samples and 0.6at% CaO was added to Er:YVO4 + CaO crystal. The resonator
mirrors were deposited directly on the crystal faces: a rear mirror was HR for the 1.6 μm wavelength and HT for
0.97 μm pumping radiation and as the output coupler a dielectric coatings with the 0.5% transmission at 1.6 μm
wavelength was prepared. As a pumping source a fiber coupled (core diameter-200 μm) laser diode emitting radiation
at wavelength 0.976 μm was used. Laser diode was operating in pulsed regime (pulse width 3 ms, repetition rate 20 Hz,
maximum mean pumping power 1.13 W). The diode radiation was focused into the uncooled microchip sample by two
achromatic doublet lenses with the focal length of 75 mm. As the result 175 mW and 152 mW output peak powers were
obtained for the Er:YVO4
and Er:YVO4 + CaO, respectively. The laser emission was observed in detail in range
1.529 μm up to 1.604 μm for Er:YVO4 microchip in dependence on pumping conditions. For Er:YVO4 + CaO crystal
1.6041 μm was generated only. Up-conversion radiation for both materials in dependence on pumping was also studied.
An analysis of the spectroscopic properties of trivalent erbium doped Yb3Al5O12 (YbAG) garnet is presented. In this
work, the authors focused attention on the up-conversion processes leading to the short wavelength emission from the
2G9/2, 4S3/2 and 4F9/2 excited states of Er3+ ions. The strong interaction between Yb3+ and Er3+ ions, responsible for the
infra-red (940 nm) induced visible emissions in the 415, 550 and 670 nm range, were observed.
In this paper we present prospecting single crystal materials for light generation. We describe basic property borates like: Ca4GdO(BO3)3-(GdCOB), Ga4YO(BO3)3-(YCOB), Sr3Y(BO3)3-(BOYS) doped with Yb, Pr, Nd, Sm, Tm. These crystals turn out laser and non linear optical (NLO) properties. We show KY(WO4)2-(KYW) and KGd(WO4)2-(KGW) belonged to double vanadates group, and flourides LiCAlF6-(LiCAF) and LiSrAlF6-(LiSAF), their properties and growth methods. Interesting group of materials which can be used as source of light are organic compounds. Examples of these materials are presented.
Solid state lasers pumped with diode form a new class of lasers which replace those with lamp pumped lasers presently used. Properties of most often discussed single crystals for diode pumped solid state lasers are presented. YAG crystals doped with Yb and double-doped with Er, Yb and YVO crystals doped with rare earth elements are discussed. Recently promising for laser application seems to be doped tungstate KGd(WO4)2 and KY(WO4)2 crystals. Relatively new group of laser materials are borates, like GdCa4(BO3)3, Ca4YO(BO3)3, YAl(BO3)3 offering laser, self-frequency doubling and nonlinear optical properties. As active laser materials fluorides are discussed e.g. doped LiCaAlF6, LiSrAlF6 crystals. Important group of materials applied in laser technique are materials showing nonlinear absorption, which are used for passive modulation (Q-switch). YAG crystals doped with Cr, V, Co are presented.
The results of examinations of spectroscopic properties and generation parameters of new active media, i.e., Er3+ and Yb3+ doped YAG crystals are given. Erbium and ytterbium doped YAG single crystals were obtained by the Czochralski method. The spectral properties and laser characteristics were investigated. Absorption spectra of Er3+ and Yb3+-doped active media were measured in the spectral range 190 divided by 5000 nm at room temperature. Excitation and luminescence spectra were also recorded at room temperature with a JOBIN-YVON spectrofluorimeter using a diode laser as an excitation source. The measurements of the lifetime of the Er3+ ions in the upper laser level of the samples were made by the direct method with pulse excitation. We present also the result of investigations on spectroscopic properties and non-linear absorption effect in YAG:Co2+ crystal-new absorber used for the systems generating giant-pulse radiation at 1.5 micrometers .
This paper describes efforts taken in Institute of Applied Physics and Institute of Electronic Materials Technology to obtain several single crystals from borate family, namely, CsLiB6)10, Ca4GdO(BO3)3, Li2B4O7, (beta) -BaB2O4, and Yal3(BO3)4, pure and doped with several ions. The main goal of this investigation was to develop technology of these new nonlinear optical materials to create possibility of their applications in higher harmonics generators and self- frequency doubling lasers. Depending on such properties of crystallized borate materials as incongruent melting or high temperature phase transitions, Czochralski technique or high temperature solution growth technique were used. The main aspects of crystallization of these materials as well as their optical properties are discussed.
This paper deals with the excitation and decay of excited state of holmium in LiTaO3 single crystals. Particular attention is paid to processes governing a population build up on the 5S2 and 5I7 metastable states whose quantum efficiencies are sufficiently high to be considered as initial levels for a laser transition. We observed for the first time, to our knowledge, an efficient conversion of the 647.1 nm light of a krypton ion laser into green luminescence in the material studied. Based upon analysis of excited state relaxation dynamics it is concluded that the mechanism involved is the excited state absorption from the long lived 5I7 level. Efficient single wavelength excitation is due to coincidence of transition energies of the ground state absorption and excited state absorption.
Crystals of Er:YVO4 were grown by Czochralski method. Uniformly doped and good quality crystals have been obtained. The lifetimes of the 4S3/2, and the luminescence dynamics were studied as a function of temperature in the region 5-500K. The green luminescence around 550 nm has been observed in excitation by the Ti:sapphire laser into 4I11/2 level. The excitation spectrum recorded for 4S3/2 has been compared with absorption cross section spectrum and calculated ESA spectrum for 4I11/2-4F7/2 transition. The contribution of ESA process in upconversion phenomenon under excitation into 4I11/2 has been assessed. The emission cross-section and the gain coefficient for 4I13/2-4I15/2 transition of Er3+ in YVO4 have been calculated.
In this communication we report initial results of studies on x-ray and VUV excited luminescence of YAP and YAG crystals activated with Pr3+ and YAP activated with Ce3+. Excitation and luminescence spectra of Pr3+ and Ce3+ d-f and Pr3+ f-f emissions and luminescence time profiles under pulsed synchrotron excitation are presented and analyzed in order to identify and characterize various host-to-ion energy transfer channels. The results support the notion that direct and trap mediated capture and recombination of holes and electrons via Pr3+ or Ce3+ ions provide the dominant mechanism of radio luminescence production in both YAP and YAG crystals.
There is considerable interest in compact pulsed high peak power laser sources emitting at wavelengths near 1.55 micrometers . Rangefinders and other applications with free space propagation could be strongly benefit of such devices. The wavelength of around 1.55 micrometers is in the eyesafe regime where significantly higher pulse energies can be used without damaging human eyes. Erbium and ytterbium doped YAG single crystals were obtained by the Czochralski method. The basis conditions of growth and the results of optical homogeneity measurements of the obtained crystals are presented. Absorption spectra of these Er3+- and Yb3+-doped YAG crystals were measured in the spectral range 190 divided by 5000 nm at room temperature. Excitation and luminescence spectra were also recorded at room temperature with a JOBIN-YVON spectro fluorometer using a diode laser as an excitation source. The measurements of the lifetime of the Er3+ ions in the upper laser level of the samples were made by the direct method with pulse excitation.
The paper describes growth of neodymium doped borate and tungstate single crystals and their optical and spectroscopic properties. Czochralski and top seeded solution growth techniques were used to crystalize Kgc1-xNdx(WO4)2 tungstate, and self-frequency doubling YAl3(BO3)4:Nd and Ca4GdO(BO3)3:Nd borates. Single crystals having good optical quality, free from inclusions, bubbles, or cracks were obtained. Transmission and luminescence spectra of investigated crystals were measured. The measurements of Nd3+ ions lifetime at the upper laser level for the samples of KGW:Nd, YAB:Nd, and GdCOB:Nd crystals were made by means of direct method with pulse excitation. The obtained results confirm usability of as-grown single crystals for construction of diode-pumped lasers.
Growth conditions for Nd:YVO4 crystals and some optical properties are presented. The obtained Nd:YVO4 crystal shows lower content of point defects and consequently, lower susceptibility to ionizing radiation. ESR measurements show the presence of V ions in interstitial sites with another than 5t valency. Obtained by Czochralski method crystals reveal very good optical properties, some of which are better than for Nd:YAG.
The results of investigations of gamma radiation influence on laser performance of Nd:SLGO, Er:YAG and CTH:YAG crystals were reported. Twice and fourfold increase of optical output was stated for Er:YAG and Nd:SLGO, CTH:YAG lasers, respectively. The increase takes place due to color centers created by gamma quanta, that is due to additional absorption bands appearing in the crystals after gamma irradiation.
The influence of gamma and electron irradiation on optical and lasing properties of Y3Al5O12, Gd3Ga5O12, YAlO3 and LiNbO3 single crystals doped with rare-earth ions was studied. The laser output energy in the Nd-doped laser crystals and (gamma) -irradiation is decreased due to passive losses on the laser generation wavelength 1.06 micrometer (reabsorption of the laser radiation by color centers). The color centers in YAG-Er crystals may fulfill the sensibilizator function providing an increase of the pumping efficiency and output energy of the laser generation at 2.94 micrometer.
Bismuth-germanium oxides (Bi12GeO20) and bismuth- silicon oxide (Bi12SiO20) single crystals doped with chromium or manganese are photochromic materials. The annealing of these materials in some atmospheres changes their optical properties. The results of experimental research are presented.
In this work, the conditions for preparation of raw material as well as the conditions for crystal growth of (gamma) - LiAlO2 and (beta) -LiGaO2 by Czochralski method were studied. As a result, single crystals of these compounds were obtained. The phases were checked by x-ray powder diffraction. High vapor pressure of the melt at the pulling temperature was identified as the main problem in the growing process. Preliminary high-resolution x-ray diffraction measurements were made, which indicated a high concentration of small defects in the LiGaO2 crystals.
Single crystals of SrLaGa3O7 doped with 0.5 and 1 at.% praseodymium were grown by the Czochralski technique. A heating system with good thermal insulation and afterheater were applied in order to achieve appropriate radial and axial temperature gradients in the crystallization chamber. Low temperature gradients and flat crystal-melt interface could provide good optical quality crystals free of internal stresses. All single crystals were grown in  direction. The pulling rate was 1.5 - 3 mm/h and the rotation rate 50 rpm. The composition and dopant's distribution in crystals were checked by x-ray microprobe. The obtained crystals up to 25 mm in diameter and up to 80 mm in length were of good quality and the dopant's distribution was uniform. The doped crystals were investigated for their spectral an lasing properties. Absorption spectra in range of 180 - 8000 nm were measured, then laser rods were cut out and their generation properties were evaluated.
Lithium niobate crystals doped with Dy3+ ions were grown by the Czochralski method. The doping concentrations were 0.3, 1, and 1.7 at.%, respectively. The dopant distribution was measured by the electron microprobe 'JOEL-JXA 50 A'-type device, and from these measurements the segregation coefficient has been found to be close to unity (k approximately equals 0.8). Optical homogeneity of crystals was investigated by the conoscopic and polarimetric methods. For the Z-optical axis direction it was found that the maximum residual birefringence (not exceeding 1.5 multiplied by 10-4), involved by residual stresses, occurred at the perimeters of the crystals, and the remaining crystalline areas were almost entirely free from excessive stresses. The absorption characteristics in the wavelength range of 200 - 6000 nm were measured. The photoluminescence characteristics were also measured in the visible part of the spectrum. It has been found that an important feature associated with luminescence of the Dy3+ in LiNbO3 is its high intensity and long decay time. From this it can be concluded that LiNbO3:Dy3+ is particularly well suited for visible lasers.
In this work the optical and lasing features of 1.2at. percent neodymium doped GGG crystals in comparison to YAG, SLGO and YAP ones are presented. Influence of UV and gamma radiations on a change of absorption and luminescence spectra of the crystal is also reported. The strong influence of UV radiation of pump lamp on lasing characteristics of GGG:Nd crystals is stated. After cut off UV from pump lamp spectrum the slope efficiency of GGG:Nd laser can be placed between SLGO:Nd and SLGO ones.
Examined praseodymium doped crystals with 1 at.% of Pr3+ ions for YAG and SrLaGa3O7 (SLGO) hosts were produced using Czochralski method. The luminescence for the range of 200 - 800 nm and absorption spectra for a wide range of 200 - 6000 nm, for Pr3+:YAG and Pr3+:SLGO crystals have been measured. It was stated that for praseodymium doped YAG and SLGO crystals, the strongest peaks of luminescence occur at 0.489 and 0.502 micrometers and the strongest peaks of absorption occur at 0.44 - 0.5 and 0.58 - 0.62 micrometers bands. A free-running laser emission of (lambda) equals 0.62 micrometers radiation for both types of crystals Pr:YAG and Pr:SLGO for two different transmissions of output mirrors have been obtained.
Nonlinear optics is a vast field requiring materials with different performance features. Rapidly developing world communication, demand for UV, blue or green light sources for computers, photolithography, color displays, etc. need novel more and more excellent nonlinear (NLO) and electro-optic (EO) materials. Many organic and inorganic crystals are presently known as the materials which can be used for these kinds of applications. Selected inorganic NLO and EO crystals used in practice are discussed and Chochralski growth of (beta) -BaB2O4 (BBO) crystals is presented.
Growth of Cr4+:YAG crystals as a relatively new laser material and their spectroscopic properties are presented. The possibilities of using these crystals for manufacturing of passive Q-switch modulators are pointed out.
LiYF4 (YLF) is a very promising host material for lasers. Investigation of the spectroscopic and physical properties of YLF:Nd has suggested that this material may be a better candidate than Nd:YAG for generating short pulses with high peak power. This is a distinct advantage for many applications. Stimulated emission is attained at 1053 nm and 1047 nm. Also upconservation laser action in YLF and YLF:Er crystals is reported. More recently YLF doped with rare-earth elements has gained some attention. Pulsed room-temperature laser action at 2.06 micrometer has been achieved using YLF:Ho sensitized with Er and Tm. Using YLF:Pr blue light emission at 479 nm at room temperature was observed. Growth experiments of YLF:Nd crystals were carried by the Bridgman method. A vacuum furnace with cylindrical molybdenum heater and graphite crucible have been used. The temperature gradient of 25 degrees Celsius/cm has been achieved by using a stainless steel liner in the lower part of the furnace. The growth was performed in a nitrogen atmosphere. First crystals of YLF:Nd have been obtained.
Potassium titanyl phosphate is actually the best non-linear optical material. Also it's very good electro-optic coefficients, low dielectric constants and large figure of merit make it attractive for practical use. Crystals can be grown by both hydro-thermal and flux methods.