Zhang Bai-Gang

Thermal Effect in KTP Crystals During High Power Laser Operation

We report on the theoretical and experimental studies of the thermal effect of the KTP crystal during high power operation. From the dependence of the refractive index temperature coefficients on wavelength, the dependence of the optimum phase-matching angles on temperature is derived. In the experiment, the angle of the frequency-doubled KTP crystal is tilted to compensate for the thermal effect and to obtain Δ = 0.7° when the green laser output power is 30 W and the KTP crystal temperature is about 80°C. We obtained the highest stable output power greater than 40 W with an L-shaped flat-flat intracavity frequency-doubled Nd:YAG laser. The experimental results are very consistent with the theoretical analysis.

Nearly-noncritical phase matching in MgO : LiNbO3 optical parametric oscillators

We have proposed and demonstrated a nearly-noncritical phase-matched (NCPM) optical parametric oscillation (OPO) in an MgO:LiNbO3 crystal with 5 mol% MgO by temperature tuning. By giving up perfect NCPM, the practical tuning range for the OPO is increased by two times. For the crystal, the operated temperature decreases with the phase-matching angle at degeneracy. With a cutting angle of 82° instead of the noncritical case of 90°, the tuning range was increased. In order to obtain a sufficiently high output pulse energy for both signal and idler throughout the entire tuning range, five sets of mirrors were used for the resonator. The tuning range of the OPO was 800-1700 nm with temperatures tuning from 83°C to 224.2°C. The output energy was about 6.45 mJ with a conversion efficiency of nearly 13%. The bandwidth of the output was 1.0-1.1 nm.

Temperature Tunable Infrared Optical Parametric Oscillator with Periodically Poled LiNbO3

We demonstrate a temperature tunable infrared optical parametric oscillator (OPO) based on periodically poled LiNbO3 (PPLN) pumped by an acousto-optically Q-switched cw-diode-end-pumped Nd:YVO4 laser with the signal output from 1.48 µm to 1.54 µm by tuning the work temperature from 60°C to 250°C and the maximum average signal power (1500 nm) of 137 mW. We report the demonstration of the sum frequency of the pump and idler in a single-grating PPLN crystal. In addition, we present the theoretical analysis of the signal wavelength change rate with the changing temperature for a quasi-phase matching OPO, which is in good agreement with our experimental results.

High-Average-Power Nanosecond Quasi-Phase-Matched Single-Pass Optical Parametric Generator in Periodically Poled Lithium Niobate

A pulsed nanosecond optical parametric generator (OPG) in periodically poled lithium niobate (PPLN) crystal is presented. The pump laser is an acousto-optically Q-switched Nd:YVO4 laser with the maximum average power of 6.58 W. When the repetition rate is 50 kHz and the pulse width of the pump source is 80 ns, the maximum average total output power of the single-pass PPLN OPG is about 1.9 W, which includes 1.322 W of 1.536 μm signal radiation. The length of the PPLN crystal is only 38.7 mm (at room temperature) with a grating period of 28.93 μm (at room temperature). The 1.502–1.536 μm signal radiation and 3.652–3.465 μm idler radiation are obtained by adjusting the PPLN crystal temperature from 155 degrees C to 250 degrees C.

Low-threshold, high-efficiency, high-repetition-rate optical parametric generator based on periodically poled LiNbO3

We report a high-repetition-rate optical parametric generator (OPG) with a periodically poled lithium niobate (PPLN) crystal pumped by an acousto-optically Q-switched CW-diode-end-pumped Nd:YVO4 laser. For the maximum 1064nm pump power of 970mW, the maximum conversion efficiency is 32.9% under the conditions of 250 degrees C, 1064nm pulse repetition rate of 22.6kHz and pulse width of 12ns and the PPLN OPG threshold in the collinear case is less than 23.7?J. The output power increases with the increase of the crystal temperature. The 1485?1553nm signal wave and 3383?3754nm idler wave are obtained by changing the temperature and the angle of the PPLN crystal.

High-efficiency single-pass cw quasi-phase-matched frequency doubling based on PP-MgO:SLT

We demonstrate a single-pass cw quasi-phase-matched (QPM) frequency doubling based on periodically poled MgO-doped stoichiometric lithium tantalate (PP-MgO:SLT) with crystal length of 20mm. For the maximum 1064nm fundamental power of 7.69W, the maximum conversion efficiency and the maximum output second-harmonic power are 11.8% and 905mW, respectively. In the experiment we found that the optimum temperature of the oven for PP-MgO:SLT should be adjusted with the change of the fundamental power and the focal length. In addition, angular acceptance bandwidth and temperature acceptance bandwidth are studied. Their experimental results are in good agreement with the theoretical calculations.

Performance of gain-switched all-solid-state quasi-continuous-wave tunable Ti:sapphire laser system

We have made a gain-switched all-solid-state quasi-continuous-wave (QCW) tunable Ti:sapphire laser system, which is pumped by a 532 nm intracavity frequency-doubled Nd:YAG laser. Based on the theory of gain-switching and the study on the influencing factors of the output pulse width, an effective method for obtaining high power and narrow pulse width output is proposed. Through deliberately designing the pump source and the resonator of the Ti:sapphire laser, when the repetition rate is 6 kHz and the length of the cavity is 220 mm, at an incident pump power of 22 W, the tunable Ti:sapphire laser from 700 to 950 nm can be achieved. It has a maximum average output power of 5.6 W at 800 nm and the pulse width of 13.2 ns, giving an optical conversion efficiency of 25.5% from the 532 nm pump laser to the Ti:sapphire laser.

High power output quasi-continuous-wave nanosecond optical parametric generator based on periodically poled lithium niobate

We report on a high power output quasi-continuous-wave nanosecond optical parametric generator (OPG) of congruent periodically poled lithium niobate (PPLN) pumped by a 1064 nm acousto-opticallyQ-switched Nd: YVO4 laser (duration: 70 ns, repetition rate: 45 kHz, spatial beam qualityM2< 1.3). The OPG consists of a 38.7 mm long PPLN crystal with a domain period of 28.93 μ. With 5.43 W of average pump power the maximum average output power is 991 mW at 1517.1 nm signal wave of the PPLN OPG.

Compact efficient optical parametric generator internal to a Q-switched Nd ： YVO4 laser with periodically poled MgO：LiNbO3

This paper demonstrates a compact efficient optical parametric generator internal to a Q-switched diode-end-pumped Nd:YVO4 laser with periodically poled MgO:LiNbO3(PPMgLN). With the Q-switch set at a repetition rate of 25kHz and the PPMgLN crystal operated at room temperature (25°C), the intracavity optical parametric generator threshold was reached as a diode pump power of 0.9 W. A maximum signal output power of 0.34 W with a pulse width of 25 ns and a beam quality factor of 1.4 was obtained at an incident diode power of 3.4 W, leading to a conversion efficiency of 10% with a slope efficiency of 14.4%. By varying the crystal temperature from 25 to 200°C, the output signal wavelengths were tuned in range of 1506-1565 nm. Over a 30-minutes interval, the instability of the signal power was measured to be less than 1%. In addition, the threshold pump intensity for the intracavity optical parametric generator is theoretically investigated, and the obtained result is in good agreement with the experimental results.

1-W, high-repetition-rate room temperature operation of mid-infrared optical parametric oscillator based on periodically poled MgO-doped LiNbO

In this paper a high-repetition-rate mid-infrared (mid-IR) optical parametric oscillator based on periodically poled MgO-doped LiNbO3 (PPMgLN) at room temperature was demonstrated. The maximum average mid-IR output power at 3.63μm was 1.02 W with the repetition rate of 60kHz and corresponding efficiency from the pump to the idler was 26.7%. The temperature tuning and the period tuning characteristics were also discussed.