Fangqin Li

High Efficiency and High Peak Power Picosecond Mid-Infrared Optical Parametric Amplifier Based on a New Crystal BaGa 4 Se 7

A high efficiency and high peak power picosecond (ps) mid-infrared optical parametric amplifier with a new nonlinear crystal BaGa(4)Se(7) pumped by a 30 ps 1064 nm Nd:YAG laser is demonstrated for the first time. The maximum photon conversion efficiency of 56% from 1064 nm to 3.9 μm idler has been achieved at the pump energy of ~1.8 mJ. A maximum idler output of 830 μJ at 3.9 μm with peak power of ~27 MW was obtained at pump energy of ~9.1 mJ. Moreover, a 3-5 μm idler tuning range was demonstrated, with output energies of ~300 μJ at 5 μm and up to 1 mJ at 3 μm at ~8.2 mJ pump energy.

High-power 880-nm diode-directly-pumped passively mode-locked Nd:YVO 4 laser at 1342 nm with a semiconductor saturable absorber mirror

A high-power 880-nm diode-directly-pumped passively mode-locked 1342 nm Nd:YVO₄ laser was demonstrated with a semiconductor saturable absorber mirror (SESAM). The laser mode radii in the laser crystal and on the SESAM were optimized carefully using the ABCD matrix formalism. An average output power of 2.3 W was obtained with a repetition rate of 76 MHz and a pulse width of 29.2 ps under an absorbed pump power of 12.1 W, corresponding to an optical-optical efficiency of 19.0% and a slope efficiency of 23.9%, respectively.

Comparison of laser induced thermal fracture between polycrystalline ceramic and crystal Nd:YAG

Continuous wave 808 nm pump laser-induced thermal damage of polycrystalline transparent ceramic and crystalline Nd:YAG materials was investigated both experimentally and theoretically. The measured temperature agrees well with the theoretical simulation, and the maximum hoop stresses occur on the incident facet of the end-pumped rod at about √2 times of the pump beam radius w0, where the temperature gradient is the highest and the damage occurs first at this location. The fracture-limited laser intensity of ceramics was experimentally measured to be 6.4±0.6  kW/cm2, nearly 64% higher than that of the crystals (3.9±0.3  kW/cm2). The deduced thermal fracture stress for ceramic was 386±50  MPa, which is 64% higher than that of the crystals (235±16  MPa).

High peak power 4.7 ns electro-optic cavity dumped TEM 00 1342-nm Nd:YVO 4 laser

We presented the first demonstration of a high-peak power few-nanosecond pulse 1342-nm Nd:YVO(4) laser by the combination of cavity dumping and in-band pumping. The maximum average output power of 3.2 W with Gaussian TEM(00) mode was obtained at the pulse repetition rate (PRR) of 10 kHz. The pulse width remained to be 4.7±0.1  ns for the PRR from 2 to 10 kHz. The maximum pulse energy of 0.55 mJ was obtained at 2 kHz and the corresponding peak power was up to 117 kW. This is, to our knowledge, the shortest ns pulse width and the highest peak power for LD-pumped 1.3 μm TEM(00) lasers with an active Q-switch device.

Transient-grating self-referenced spectral interferometry for infrared femtosecond pulse characterization

We propose a technique for measuring infrared femtosecond pulses: transient-grating self-referenced spectral interferometry. Based on this technique, we built an extremely simple, alignment-free device and successfully characterized both 38 fs pulses at 800 nm and sub-two-cycle 10 fs pulses at 1.75 μm.

High-Power Ultraviolet 278 nm Laser from Fourth-Harmonic Generation of a Nd:YAG Laser in CsB 3 O 5

We demonstrate a high-power UV 278 nm laser by fourth-harmonic generation (FHG) of a 1112 nm Nd:YAG laser in a nonlinear optical (NLO) crystal CsB3O5 (CBO) for the first time, to our best knowledge. A 30 W level diode-pumped Q-switched Nd:YAG laser at 1112 nm with beam quality factor M2=1.2 was used as the fundamental light source at a pulse width of 500 ns. With an LiB3O5 crystal, the 1112 nm laser was first frequency-doubled to 556 nm with an average output power of 13.5 W. It was then frequency doubled again in a CBO crystal to obtain the FHG output at 278 nm. The maximum average output power of the 278 nm laser is up to 1.5 W. The results demonstrated that CBO crystal is a promising NLO material for UV high-power lasers below 300 nm.

High-power diode-side-pumped rod Tm:YAG laser at 2.07 μm

We report a high-power diode-laser (LD) side-pumped rod Tm:YAG laser of around 2 μm. The laser was water-cooled at 8°C and yielded a maximum output power of 267 W at 2.07 μm, which is the highest output power for an all solid-state cw 2.07 μm rod Tm:YAG laser reported as far as we know. The corresponding optical-optical conversion efficiency was 20.7%, and the slope efficiency was about 29.8%, respectively.

High-Efficiency 2-mJ 5-kHz Picosecond Green Laser Generation by Nd:YAG Innoslab Amplifier

A high-efficiency picosecond (ps) 532-nm green laser with high pulse energy and high peak power at 5-kHz repetition rate was demonstrated by second-harmonic generation (SHG) from a 1064-nm master oscillator power amplifier (MOPA). The MOPA was based on the Innoslab structure under diode directly pumping, producing 4.8-mJ, 25-ps fundamental laser at the repetition rate of 5 kHz after a three-stage Innoslab amplification system. With a pulse energy of 2.93 mJ in the fundamental and using a type I noncritically phase matched lithium triborate crystal, the pulse energy of SHG was up to 1.96 mJ per pulse with a pulse width of 18.9 ps, which corresponds to a peak power of 104 MW in the green and SH conversion efficiency as high as 67%. The SHG green beam quality factor was measured to be M2 = 1.75.

Confocal Fabry-Perot interferometer for frequency stabilization of laser

The frequency shift of laser source of Doppler lidar is required in the range of a few megahertzs. To satisfy this demand, a confocal Fabry-Perot (F-P) interferometer was manufactured as the frequency standard for frequency stabilization. After analyzing and contrasting the center frequency shift of confocal Fabry-Perot interferometers that are made of three different types of material with the change of temperature, the zerodur material was selected to fabricate the interferometer, and the cavity mirrors were optically contacted onto the end of spacer. The confocal Fabry-Perot interferometer was situated within a double-walled chamber, and the change of temperature in the chamber was less than 0.01 K. The experimental results indicate that the free spectral range is 500 MHz, the full-width at half maximum is 3.33 MHz, and the finesse is 150.

Passively mode-locked grown-together composite YVO4/Nd:YVO4 crystal laser with a semiconductor saturable absorber mirror under 880-nm direct pumping

A passively mode-locked grown-together composite YVO4/Nd:YVO4 crystal laser is demonstrated with a semiconductor saturable absorber mirror by 880-nm laser-diode direct pumping. Under the absorbed pump power of 24.9 W, a maximum output power of 10.5 W at the repetition rate of 77 MHz is obtained, corresponding to the optical-optical conversion efficiency of 42.1% and the slope efficiency of 53.4%. The pulse width measured is 33 ps at the output power of 10 W.