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:YAlO<sub>3</sub>(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 % Ho<sup>3+</sup>-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 M<sup>2</sup> 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 M<sup>2</sup> 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.
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.