Using a YVO4/Nd:YVO4/YVO4 composite crystal end pumped by laser diode, we demonstrate the simultaneously Q-switched and mode-locked self-Raman laser at the firststokes wavelength of 1176.07 nm. Its corresponding linewidth was measured to approximately be 0.14 nm. At the pump power of 38 W and the pulse repetition frequency of 50 kHz, the maximum average output power at 1176 nm was obtained to be 1.34 W with the corresponding optical conversion efficiency of 3.6%. The highest pulse energy and the highest peak power were obtained to be 35 μJ and 10.5 kW, respectively. The shortest mode-locked pulse width of the laser was obtained to be ~300 ps with the corresponding repetition rate of mode-locked laser pulse is ~ 1.11 GHz
KEYWORDS: Femtosecond phenomena, Sensors, Temperature metrology, Structured optical fibers, Temperature sensors, Lithium, Single mode fibers, Michelson interferometers, Interferometers, Head
A 45° fiber cantilever beam for high temperature measurement was fabricated by femtosecond laser in single mode fiber. The temperature sensitivity is obtained to be about 17 pm/℃ at 800 ℃ and 1560 nm. The 45° fiber cantilever beam possesses good repeatability and stability in high temperature. The sensor is small in size, cheap and good stability.
We demonstrate a technique called “In volume Selective Laser Etching” (ISLE) to combine femtosecond laser modification technique with chemical etching for the fabrication of microchannels in the aluminosilicate glass. The influence of laser power on the length-diameter ratio of microchannels is studied. We fabricated tapered aluminosilicate glass microchannels with diameters from 30 to 50 μm. We used the same method to modify surface of aluminosilicate glass, and obtained taper-free microgrooves with a width of 50 μm. The microgrooves had no length limitation. In industrial production, the surface roughness was also improved in this way.
This paper demonstrate an intracavity Raman laser at 2291 nm by using YVO4 crystal as Raman crystal to achieve efficient Raman conversion in a compact diode-end-pumped actively Q-switched Tm:YLF (Tm3+-doped lithium yttrium fluoride) laser with an L-shaped cavity. With a pump source of fiber-coupled continuous-wave diode laser operating at 793 nm, the Tm:YLF crystal served as gain material in the Raman laser. We made experimental research on the characteristics of first-Stokes Raman laser output the different pulse repetition rates (PRFs). The maximum average output power, pulse width and the corresponding peak power were 175.2 mW, 21.41 ns and 1.63 kW respectively at a pluse repetition frequency of 5 kHz and an incident pump power of 21W.
Rotating mirror is not only as an imaging element in optical path of ultra-high speed camera, where imaging quality is affected by surface quality and plane deformation of the rotating mirror, but also as an element to implement ultra-high speed, because performances of the ultra-high-speed camera system are mainly dependent on the static and dynamic mechanical properties of the rotating mirror. In this paper, the static and dynamic properties of magnesium alloy rotating mirror with equilateral-triangle cross-sections were investigated by theoretically and numerically method. At the speed of 2×105 rpm, the maximum lateral deformations of the mirror facet with width 17.32 mm and length 40 mm is 2.476 μm. The maximum von Mises stress is 35.1 MPa. The deformation and stress are less than that of aluminum alloy rotating mirror, which has been successfully applied in many types of RM for ultra-high speed cameras. The first three frequencies of magnesium alloy rotating mirror are 9,539.9 Hz, 9,540.9 Hz and 12,726.0 Hz, respectively. While the first three frequencies of aluminium alloy rotating-mirror are 9,683.9 Hz, 9,685.2 Hz and 11,016.0 Hz. From which it is preliminarily shown that a magnesium alloy rotating mirror can be used as replacement for an aluminium alloy rotating mirror in ultra-high-speed camera.
A high power diode-pumped continuous-wave Tm:YAP laser with a piece of silicon chip as the output coupler (Si-OC) is demonstrated. A maximum output power of 13 W with a beam quality of M2 ≤ 1.45 at 1931 nm was obtained, corresponding to an optical-to-optical efficiency of 31%, and a slope efficiency of 33%. To our best knowledge, this is the first report of utilizing silicon as a output coupler on solid Tm:YAP laser system. The mechanism of silicon output coupler on Tm:YAP laser is also discussed in this letter. Because of the intriguing characteristics of silicon, such as high damage threshold, low cost and long-pass filter property, double-sided polishing single crystal silicon chip can perform as a good output coupler in high power laser system near 2 μm region.
A novel and compact fiber-probe pressure sensor was demonstrated based on micro Fabry-Perot interferometer (FPI). The device was fabricated by splicing both ends of a short section simplified hollow-core photonic crystal fiber (SHCPCF) with single mode fibers (SMFs), and then a micro channel was drilled by femtosecond laser micromachining in the SHC-PCF to significantly enhance the pressure sensitivity. The pressure sensing characteristics based on micro-FPI have been investigated by measuring the signals through the demodulation of phase since the external signal imposing on the interferometer will induce the phase change of interference signal. Then a FBG was cascaded to demodulate the signal. A micro FPI demonstrates a maximum pressure sensitivity of 32 dB/MPa, while a low temperature cross-sensitivity of 0.27 KPa/°C. Hence it may have potential for pressure applications in harsh environment.
Long period fiber grating (LPFG) upon all-solid photonic bandgap fiber with a bandgap at 1.068 to 1.180 μm is fabricated by high-frequency CO 2 laser pulse irradiation. The resonance wavelength is 1335.76 nm with a modulation depth of 15 dB and a 3-dB bandwidth of 2.6 nm. Bending response of the LPFG is dependent on the axial orientations and the input polarization states. The maximum bending sensitivity is achieved at 52 nm/m . The temperature response is weakly dependent on the polarization state, and is achieved around 20.47 pm/°C at a 0-deg polarization azimuth. The bending measurement error resulting from temperature can be negligible within the range of 0.4 to 0.82 m −1 . It is be beneficial to avoiding cross-sensitivity of temperature in bending measurements.
A high power diode-pumped composite YVO4/Nd:YVO4/YVO4 actively Q-switched and mode-locked laser with ring
resonator is demonstrated. For mode-locking operation, the maximum average output power at 1064 nm was up to 14.4
W at a pulse repetition frequency (PRF) of 85 kHz and at the incident pump power of 40 W, with the corresponding
optical conversion efficiency of 36%. The shortest mode-locked pulse width was obtained to be 117.1 picosecond (ps) at
the incident pump power of 26 W and PRF of 55 kHz, with the corresponding average output power of 7.37 W and the
linewidth of 0.0436 nm. The highest pulse energy and peak power were obtained to be 93.5 μJ and 0.362 MW at PRF of
5 kHz and incident pump power of 40W, respectively.
A 30-mm-length YVO4/Nd:YVO4/ YVO4 composite crystal was used as self-Raman gain material. Yellow
radiation at 587 nm was obtained by utilizing a 15-mm-length LBO as frequency-doubling crystal. The maximum
average power at 587 nm is up to 8.05 W at the pulse repetition rate of 50 kHz and the pump power of 65 W, with
the corresponding optical conversion efficiency of 12.38%. The shortest pulse width, the highest peak power and the
maximum pulse energy were measured to be 5.57 ns, 22.1 kW, and 161 μJ, respectively.
Long period fiber gratings (LPFGs) with different periods in the standard single mode fiber were
fabricated, using laser direct writing method, by femtosecond laser pulses with pulse width of 200 fs
and the repetition rate of 250 kHz at a center wavelength of 800 nm in air. Comparative with bare
LPFG in temperature sensor, LPFG had been encapsulated using large coefficient of thermal
expansion of epoxy polymer and Aluminum to enhance the temperature sensitivity. The results
showed that the temperature sensitivity of encapsulated LPFG was 2 times than that of bare LPFG.
In addition, we also researched the relationship between resonant wavelength and surrounding
refractive index (SRI) when LPFG immersed in refractive index of solution of different index at
20 degree Celsius.
Two kinds of supercontinuum (SC) sources are successfully generated by propagating 200-fs unamplified and amplified
pulses through a 0.85-m long nonlinear photonic crystal fiber (PCF), respectively. The spectra bandwidth of
amplified-femtosecond-pumped SC is about 870 nm spanning 480 nm to 1350 nm, which is flat to 1.2dB over 100 nm
spreading from 550nm to 650 nm. With the same PCF, SC spectra pumped by unamplified-femtosecond-pulses are
narrower and unevener. A detailed simulation is carried out to help us understand the mechanism of supercontinuum
evolution. For pump wavelength located at the zero dispersion wavelength of the PCF, spectra are broadened by the
interaction between SPM and higher-order dispersion at early stage. With increasing the pump power, the spectra are
broadened by fission of higher solitons and parametric four-wave mixing (FWM). When the peak power is up to
mega-watt, FWM plays a notable role in flattening and further broadening the supercontinuum spectra in short
wavelength side. An effective way to generate a flat SC laser source pumped by femtosecond pulses is also
demonstrated.
LD-pumped all-solid-state yellow laser based on frequency-doubled Nd:YVO4 crystal self-Raman laser was demonstrated. Through extracavity frequency-doubling with KTP crystal, the maximum average output power of the yellow laser was measured to be 495 mW with the incident pump power of 18 W. The corresponding optical conversion efficiency was about 2.75 %. The highest pulse energy, the shortest pulse width and the highest peak power of the yellow laser were obtained to be 19.9 μJ, 4.5 ns and 3.88 kW, respectively.
Femtosecond laser micromachining of solid materials such as Si, GaAs, polymethyl methacrylate (PMMA) and Fused
Silica has been performed in air. Femtosecond (fs) laser pulses with pulse duration of 180 fs and output wavelength of
800 nm is applied for a light source. The relationship between pulse energy and sub-micron scale crater on the surface of
Si, GaAs, PMMA and Fused Silica induced by fs laser pulses has been figured out. The sub-micron void can be
produced in the focal point of fs laser beam. Two kinds of gratings have been fabricated on the surface of Fused Silica by
femtosecond laser machining (FLM). The parameters of one grating such as the length of 20 mm, the width of 1.5 mm
and the period of 2 μm have been obtained. A 20-mm-long and 0.45-mm-wide grating with period of 11 μm has been
also fabricated. The diffraction efficiency of each order has been measured. An elliptical cross section waveguide has
been obtained inside the bulk of Fused Silica. The distance beneath the surface was measured to be 2 mm. The
diffraction rings can be observed in the far field image of the light output from the waveguide.
Rod-type photonic crystal fibers (PCFs) bring enormous advantages in Q-switched fiber laser with high pulse energy, short pulse width and good beam quality for its large mode area and short fiber length. In this paper, an acoustic-optic Q-switched photonic crystal fiber laser was investigated by using a 1m-long Yb-doped large mode area rod-type photonic crystal fiber as gain medium. A maximum pulse energy of 0.78 mJ (21.7 KW peak power) and the shortest pulse width of 20 ns were obtained at low repetition rates. A maximum 1033.6 nm average power of 14.5 W was demonstrated at 65 KHz with a slope efficiency of 56%. Further improvements would be obtained by optimizing the experiment configuration so as to achieve shorter pulse width and higher pulse energy.
To our best knowledge, the most supercontinuum sources generated by use of cw pump lasers were obtained with fiber
interaction lengths of the order of 100 m to a few kilometers to enhance the optical nonlinearity. However, the material
loss was accumulated and the price cost was boosted in the long fibers. In this paper, CW supercontinuum generation by
use of a 1480-nm fiber-Raman laser (FRL) in a 100-m high-nonlinear photonic crystal fiber (PCF) together with a 76-km
single mode fiber (SMF) was demonstrated. The broadband supercontinuum was obtained with 10-dB bandwidth of 124
nm spanning from 1476 to 1600 nm. It was shown that the principal mechanism of the broadening could be assigned to
stimulated Raman scattering, four-wave mixing (FWM) and modulation instability (MI).
We report a high-power diode-double-end-pumped Q-switched Nd:YVO4 red laser through intracavity
frequency-doubling with a type-I critical phase-matched LBO crystal. At the repetition frequency of 26 kHz, the
maximum quasi-continuous-wave (QCW) output power at 671 nm was measured to be 9.2 W at the incident pump power
of 62.4 W with the corresponding optical conversion efficiency of 14.7%; the pulse width of about 106 ns; the pulse
energy of 353.8μJ; the peak power of 3.34 kW, respectively. The perfect performance indicated that the
double-end-pumped technique could effectively diminish the thermal lens effect, extend the range of the stable resonator
region and achieve a high optical conversion efficiency to obtain a high output power.
With an acousto-optical Q-switch and Co:LaMgAl11O19(Co:LMA) crystal as the saturable absorber, diode-end-pumped actively and passively Q-switched Nd:GdVO4 lasers at 1.34 μm were demonstrated, respectively. For acousto-optical Q-switched operation, the maximum average output power, the highest pulse energy, the shortest pulse width and the highest peak power were obtained to be 4.54 W, 223 μJ, 19 ns and 11.75 kW, respectively. For passively Q-switched operation with a 0.3-mm-long Co:LMA crystal as the saturable absorber, the maximum average output power, the highest pulse energy, the shortest pulse width and the highest peak power were obtained to be 1.43 W, 112 μJ, 55 ns and 1.95 kW, respectively.
Supercontinuum was generated in a polarization-maintaining (PM) PCF. The main advantage with the PM-PCF is the preservation of the state of polarization of the field propagating. For several applications, it is essential that the output has a well-defined polarization. In addition, the preserved polarization enhances the nonlinear interactions so that less power is required to generate the SC. The field patterns, birefringence and nonlinearity in the PM-PCF were simulated using a full-vector finite element method. Spectral broadening was achieved pumped by the optical parameter amplifier system (OPA). It was concluded that the SC generation was depended on the pump wavelength, and the difference group velocities in the two sides of the zero dispersive wavelength of the PCF and the OH absorption at about 1.4μm in the PCF affected the flatness of the generated supercontinuum. When the pump wavelength lied further away from the zero dispersive wavelength, the flatness was reduced, even in the visible region the blue-shift peaks were separated and didn't come into being supercontinuum. Supercontinuum with a broad bandwidth of 300 nm to 1350 nm was generated when the pump wavelength of 1200 nm, and the generated spectral bandwidth was beyond two octaves.
The absorption spectrum from 300 to 1000 nm and emission spectrum from 960 to 1450 nm of Nd:LuVO4 crystal were measured. A LD-end-pumped passive Q-switched Nd:LuVO4 laser was reported. With a Cr4+:YAG crystal as the saturable absorber, the maximum average output power was measured to be 4.58 W, and the corresponding optical conversion efficiency was 24.0 %, with the pulse energy, peak power, and pulse width being 36.6 μJ, 436.2 W, and 84 ns, respectively.
We report a high-power diode-single-end-pumped continuous-wave and Q-switched Nd:GdVO4 red laser through intracavity frequency-doubling with a type-I critical phase-matched LBO crystal. The maximum CW output power at 671 nm was measured to be 2.1 W at the incident pump power of 30 W, with the corresponding optical conversion efficiency of 7%. At the repetition frequency of 47 kHz, the maximum average output power of quasi-CW red light was obtained to be 6 W, with the corresponding optical conversion efficiency of 12.8% and the pulse width of about 97 ns. At the average output power around 5 W, the power stability was better than 5.8% for one hour. The M2 factor increased from 1.33 to 2.47 when the output power was increased from 1 W to 6 W. At the repetition rate of 25 kHz, the maximum pulse energy of 212 μJ was obtained with the corresponding peak power of 3.98 kW.
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