We reported a hybrid pumped gain-switched thulium-doped fiber laser (HP-GS-TDFL) at 2042nm in an all-fiber structure. The resonator consists of 0.7m 10/130 single-mode (SM) TDF with a pair of fiber Bragg gratings (FBG) at 2042nm, pumped by a 1550nm nanosecond fiber laser and a 793nm continuous wave (CW) laser diode (LD). Under 1550nm pulse single pump configurations, the GS-TDFL does not reach the lasing threshold at 50kHz and produces <1 μJ energy at 25kHz. Under hybrid pump configurations, the GS-TDFL produces 26μJ energy with 161ns pulse durations at 50kHz and 38μJ energy with 103ns pulse durations at 25kHz. The signal-to-noise ratio (SNR) of the output spectrum at 50kHz is 47dB. The experiment results show that pulses with higher peak power and shorter durations can be obtained by applying the hybrid pump scheme.
We developed a high-power thulium-doped fiber laser at 1907 nm with a dual-path configuration. The laser comprises a low-power seed oscillator and dual-path master oscillator power amplifiers (MOPAs). The laser has a central wavelength of 1907.4 nm and a 3 dB linewidth of 0.16 nm, with a maximum output power. Under full power conditions, the laser achieved an average output power of 154 W and 152 W. The dual-path amplifiers have a slope efficiency of 56% and 55.2%. The beam quality M2 factor is about 1.5, which is recorded at the maximum operating power.
Most of the FBGs used in continues-wave thulium-doped fiber lasers are made in foreign companies. So we built up a fiber Bragg grating (FBG) writing platform to produce different parameter FBG for research, and a homemade FBG-based thulium-doped fiber laser testing system was experimentally demonstrated in this paper. Here homemade uniform FBGbased thulium fiber laser output characteristic was explored. The thulium-doped fiber laser was built up with two 793nm laser diodes as pump source, a thulium-doped fiber, a combiner and a pair of homemade FBGs. A 1916 nm thulium-doped fiber laser with output power of 20.87 W and slope efficiency of 41.29% and a 1917 nm thulium-doped fiber laser with output power of 19.53 W and slope efficiency of 38.56% were obtained by optimizing the thulium-doped fiber length, the operation temperature of the grating and the center wavelength of the grating.
We demonstrated a stable fiber laser setup for real-time monitoring of Tm-doped gain fibers while being exposed to gamma-rays. The output power is about 10W, and the power stability of the system is ±0.25% based on the 12-hour continuous measurement. By using this laser setup and 60Co gamma-ray irradiation source, the dose rate effect and total dose effect on the typical Tm-doped fiber specimens under water-cooling condition were experimentally studied. According to the obtained experimental results on five kinds of Tm-doped gain fiber from different R and D institutions and batches at home and abroad, the output power declines monotonously with the total irradiation dose increasing. During a dose rate range of 0.05 to 0.5 rad(Si)/s, the dose rate effects of Tm-doped gain fiber samples basically disappear, which means the differences of power degradation under different dose rate are almost invisible.
We report a 2 μm band high power pulsed all-polarization maintaining (PM) thulium-doped fiber laser based on the acousto-optic q-switching technique. It is constructed in a two-stage master-oscillator power amplifier (MOPA) configuration. A Q-switched seed laser was composed of a homemade 1559 nm fiber laser, a pair of fiber Bragg gratings (FBGs) with central wavelength at 2009 nm, a piece of single-cladding thulium-doped fiber (TDF) and an acoustic-optical modulator (AOM). Using a two-stage amplifier seeded by an acousto-optic modulator modulated pulsed laser, We achieved the laser with a central wavelength of 2009.71 nm, and the laser has a 3 dB linewidth of 0.09nm and output power of approximately 2.04 W. Based on the acousto-optic switch, the pulse width of 97 ns at a repetition rate of 20 kHz was obtained. The maximum peak-power of the fiber power amplifier is 2.1 kW and pulse energy is more than 204 μJ. This high power thulium-doped fiber laser has an all-fiber based configuration. We used a cladding power stripper (CPS) with matched passive fiber to remove residual pump light that leaked into cladding. The slope efficiency of the thulium-doped fiber power amplifier was 22.7%.
The high power infrared 2μm lasers have been extensively investigated for a number of commercial, scientific and engineering applications, such as remote chemical sensing, medical diagnostics, eye-safe laser radar, and environmental monitoring. Furthermore, high-power 2μm lasers are effective pump sources of optical parametrical oscillators and optical parametrical amplifications to generate mid-infrared 3-5μm laser. In recent years, Ho:YAlO3(Ho:YAP) crystal has drawn great attention as a promising efficient laser material for its long emission wavelength at 2118nm. An acoustic-optical Q-switched Ho:YAP laser pumped by an all fiber thulium-doped fiber laser is demonstrated. The all fiber thulium-doped fiber laser can emit 80W output power, and the output laser wavelength is 1915nm. By using this 1915nm laser to end pump the AO Q-switched Ho:YAP laser system, 2118nm laser with 30W average power and 45ns pulse width at 20kHz repetition rates was obtained.
A tunable dual-wavelength passively mode-locked thulium-doped fiber laser (TDFL) based on single-wall carbon nanotube is demonstrated. By properly tuning the pump power and the polarization controller, both single- and dual-wavelength mode-locked operation can be achieved. The repetition rates of the single- and dual-wavelength mode-locked operation are both 17.64 MHz. The duration of the ultrashort soliton pulse is about 3.7 ps. By appropriately adjusting the polarization state of the laser, the dual wavelength can be tuned from 1879.8 and 1894.5 nm to 1903.3 and 1914.1 nm.
We report on the continuous wave operation of a Ho:YAP laser pumped by an all-fiber Tm-doped fiber laser, the pump laser wavelength is 1.915μm and the output laser wavelength is 2.118μm. The all fiber Tm-doped fiber laser has 70W max output power with 200W pumped power, and the output laser wavelength is 1.915μm. And this laser is used as pump laser to a Ho:YAP laser system. 20.2W CW laser power is obtained from a 0.5 at % Ho3+-doped YAP crystal at 2118.4nm with slope efficiency of 72%.
We report a high average power pulsed Tm-doped fiber laser with one stage MOPA (master oscillation power amplifier) structure. The seed source is an AOM (acousto-optic modulation) Q-switched thulium fiber laser with an average power of 2W, the wavelength is 1996.7nm, and the line-width is about 0.1nm. By one stage MOPA, we obtain the maximum average output power of 16W with nanosecond pulse width at 41kHz repetition rate, the central wavelength is 1996.7nm, and the pulse width is less than 200ns, the polarization extinction ratio is better than 20 dB. The optical-tooptical conversion efficiency is 41%, and no nonlinear effect is observed.
The propagation and split of the filamentation of femtosecond pulses in air have been paid much attention since last a few years. However, most research works are performed with few considerations of the turbulence effects of atmosphere due to the difficulties of utilizing analytical solutions and experiment conditions. In this work, we will attempt to introduce a kind of numerical simulation method to analyze the transmission features of femtosecond laser pulses in air or in the turbulent air, namely, it is called multi-phase screen method (MPSM) which use phase screen to simulate atmospheric turbulence. In this presentation, the main laser parameters are as follows: 85 fs pulse-width, 0.8cm radius of the beam, the two kinds of 160GW and 1.0 TW peak-power operating at 800 nm. Then utilizing the structure of Vortex soliton to control the filamentation is proposed. In our cases, four Gaussian pulses with a difference of π/2 in the phase of each adjacent beam as a ring to control the filamentation by utilizing its characteristics of the vortex soliton. Some results show that the coupling and interaction among four Gaussian pulses cause the rotational transfer of the energy of the four beams. Finally, we obtain the transmission features of the beams propagating in the turbulent air with different intensities by the MPSM.
Cross relaxation (CR) process in thulium ions is described. Performance of Tm-doped fiber lasers with different dopant concentrations is evaluated numerically with and without CR. Simulation shows that CR process can not only improve the slope efficiency and output of the laser system, but also lower the lasing threshold and extend the growth momentum of the laser performance. Backward LD-clad-pumped Tm-doped fiber lasers are built with Tm-doped fibers of different doping levels. A maximum output of 35.3W around 2μm is obtained with a slope efficiency of 47.2% from the 4.5wt.%- doped fiber laser while a higher slope efficiency of 54.1% was achieved from the 6.8wt.%-doped fiber laser. And, modeling shows that these laser systems are much more efficient than that without CR process.
Recent progress in the research of a diode pumped, single-frequency 355nm laser for direct-detection wind lidar is
presented. An injection seeded Nd:YAG laser was designed and built. A 'delay-ramp-fire' technique is used to achieve
single-longitudinal-mode and stable energy. In this technique, stable time relation between the resonance peak and the
pump pulse is achieved by feedback controlling the delay time between the pump pulse and the ramp voltage. The resulting
single frequency pulses are amplified and frequency tripled. This laser operates at 100Hz and provides 30mJ/pulse of
single-frequency 355 nm output with M2 value of <1.5. The frequency stability of the injection seeded Nd:YAG laser was
investigated. The piezo hysteresis is found to be the main reason to cause the frequency unstability. In an environment
avoiding high frequency vibration the frequency stability is determined by the motion linearity and ramping speed of the
piezo actuator. A modified approach is proposed to improve the frequency stability of an injection seeded laser.
A compact diode-pumped, injection-seeded and frequency- tripled Nd:YAG laser was developed for a mobile, direct detection Doppler wind lidar system. The laser is configured with the master oscillator power amplifier (MOPA). The oscillator consists of E-O Q-switched, thermal stability, diode pumped cavity. The oscillator is injection seeded by a monolithic, diode-pumped Nd:YAG seeder laser with power of 200mW. The technique of resonance detection is used to lock slave laser frequency in order to satisfy with the mobile environment. The output laser from oscillator is single-way amplified. Frequency triple is realized with a Type II KTP crystal and Type I BBO. The laser can be working on single frequency without mode jumping. The output pulse is about 15 ns at 355 nm, the linewidth is reached to the limit of Fourier transfer. The output energy is 100 mJ of 1064 nm at 100 Hz, and the beam quality is about M2 of 1.3 at both directions. The frequency- triple efficiency is over than 30%. After a long time test, the laser will be installed on a mobile lidar system.
KEYWORDS: Fizeau interferometers, LIDAR, Doppler effect, Sensors, Interferometers, Reflectivity, Laser stabilization, Signal detection, Wind energy, Signal to noise ratio
Fringe technique is preferred to edge technique of wind measurement in troposphere for a direct-detect Doppler wind lidar. However, most fringe-technique based Doppler lidar systems have been developed to date are based on conventional Fabry-perot interferometer. The purpose of this paper is to introduce our development of fringe-technique lidar based on Fizeau interferometer in which the signal can be detected more conveniently using commercial linear detector. The pre-development of the lidar system is described including interferometer's optimum design, the frequency stabilization of Fizeau interferometer and the choice of multi-anode detector. In additional, the wind error of the system is simulated with taking account of Rayleigh noise. Results shows that the wind error can be less than 0.56m/s under 5 km with 30s integral time.
An optimization model of laser diode (LD) pumped, passively Q-switched, intracavity frequency doubled solid state laser was proposed. The output energy is maximized by optimizing the length of doubling crystal and the initial transmission of saturable absorber. It provides a design criteria of a compact laser source for micro pulse lidar (MPL). The pulse repetition frequency (PRF) is controlled to meet the requirement of MPL. Numerical simulation examples are present to shows the relationship between the output energy and optimized parameters.
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