Keming Du

Electro-optically Q-switched Nd:YVO4 slab laser with a high repetition rate and a short pulse width

We report on a compact and highly efficient diode-end-pumped TEM00 Nd:YVO4 slab laser with an output power of 103 W and beam quality M2 < or = 1.5. The optical-to-optical efficiency was 41.5%. In electro-optically Q-switched operation, 83 W of average power at a pulse-repetition rate of 50 kHz with a pulse length of 11.3 ns was obtained. At a pulse-repetition rate of 10 kHz, 5.6 mJ of pulse energy, and 870 kW of peak power were measured.

High efficiency 165 W near-diffraction-limited Nd:YVO 4 slab oscillator pumped at 880 nm

We demonstrate a compact, efficient Nd:YVO(4) stable-unstable hybrid slab oscillator that was partially end pumped at 880 nm. A maximum output power of 165 W at 1064 nm was obtained with an optical-to-optical efficiency from absorbed pump power to laser output of up to 60% and a slope efficiency of up to 66%. The beam propagation factors M(2) were 1.7 in the stable direction and 1.4 in the unstable direction without sidelobes.

Diode-end-pumped double Nd:YLF slab laser with high energy, short pulse width, and diffraction-limited quality

We have developed a novel electro-optic Q-switched diode-end-pumped solid slab laser that combines high energy, short pulse width, high repetition rates, and diffraction-limited beam quality. With two partially end-pumped Nd:YLF slabs and a 100 mm long off-axis positive branch stable-unstable oscillator, 24.2 mJ, 7.1 ns electro-optic Q-switched pulse at 1 kHz repetition rate with a beam quality of M(x)(2)=1.4 and M(y)(2)=1.3 was generated. The peak power reached 3.5 MW. Efficient external second-harmonic generation was achieved by use of lithium triborate with low peak-power intensity.

Diode-end-pumped, electro-optically Q-switched Nd:YVO 4 slab laser and its second-harmonic generation

We describe the operation of a near-diffraction-limited, 1,064-nm electro-optically Q-switched Nd:YVO4 slab laser that is end pumped by laser-diode stacks and its efficient second-harmonic generation by using a lithium triborate (LBO) crystal. The energy per pulse of 3.6 and 0.8 mJ and pulse widths of 5 and 13.5 ns were obtained at repetition of 5 and 40 kHz, respectively. With a LBO crystal, a maximum output power of 15.6 W at 532 nm was obtained at the repetition rate of 40 kHz, the corresponding conversion efficiency was 60%, and the pulse width was 11.3 ns. At 10 kHz, the pulse energy of 532 nm was 1.2 mJ, and the pulse width was 5 ns.

Diode-pumped efficient slab laser with two Nd:YLF crystals and second-harmonic generation by slab LBO.

We demonstrate a diode-pumped electro-optical Q-switched slab laser with a high optical efficiency, high pulse energy, and short pulse width with two Nd:YLF crystals inside one resonator. The single compact slab resonator can generate a 1D top-hat beam at both the far field and the near field. With a slab-geometry-design lithium triborate (LBO) crystal, efficient critical phase-matching second-harmonic generation for a 1D top-hat beam with multiple transverse modes is achieved.

Nd:YAG slab laser end-pumped by laser-diode stacks and its beam shaping

Abstract An efficient high power cw Nd:YAG slab laser, partially end-pumped by diode laser stacks, and a novel beam shaping technique are reported in this paper. The optical efficiency amounted to 44% and the slope efficiency to 55%. Introducing an intracavity Brewster plate to polarize the laser beam, an optical efficiency of 35% and a slope efficiency of 41% was obtained. The output beam was rectangular and the beam quality asymmetric in two orthogonal directions. To equalize the beam quality, a step mirror beam shaping technique was introduced. The beam shaping technique and the results obtained with it are discussed in this paper.

Fiber-coupling technique for high-power diode laser arrays

Monolithic linear arrays of diode lasers, also known as diode laser bars, are the basic elements for most high-power laser applications such as solid-state laser pumping or material processing. Cylindrical microlenses used as fast- axis collimators for 10-mm diode bars require very high angles of aperture (up to 100 degree FW1/e2, equivalent to a numerical aperture of approx. 0.8) to capture most of the emitted laser power. For the efficient longitudinal pumping of laser rods, or the narrow focusing of the diode laser radiation (fiber coupling, material processing), high- quality microlenses with small lens aberrations are necessary to avoid power losses and beam quality degradation. A technique for coupling the output of high- power diode laser bars into one multimode fiber with high efficiency, easy alignment requirements and low manufacturing costs is demonstrated using a single fiber with core diameter down to 400 micrometers . This technique comprises two micro step-mirrors for beam shaping. The overall efficiency from one diode-laser bar to fiber is 71% with 20 W cm laser power through the fiber. Coupling of 12 diode laser bars and power of 200 W out of a fiber with core diameter of 0.8 mm and NA equals 0.2 is achievable with this technique.

Beam shaping and fiber coupling of high-power diode laser arrays

A technique for coupling the radiation of a high-power diode laser bar into one multimode fiber with high efficiency, easy alignment requirements and low manufacturing costs is demonstrated using a single fiber with 400 micrometers core diameter. The principal item of the fiber-coupling system is a pair of micro step-mirrors--a novel design for beam shaping. The overall efficiency from diode-laser to fiber is 71% with 20 W cw laser power through the fiber. Polarization and wavelength multiplexing renders the system scaleable to higher output power which makes it highly suitable for material processing and pumping of lasers.

Diode-end-pumped electro-optically Q-switched Nd:YLF slab laser

We report a very compact Nd:YLF slab laser that is end pumped by a quasi-continuous-wave diode stack. A hybrid resonator is used to generate high output power in a near-diffraction-limited beam (i.e., a beam propogation M2 factor of less than 1.2). A pulse energy of 14.3 mJ was obtained with a pulse width of 8.5 ns at a repetition rate of 500 Hz, which corresponds to a Q-switched peak power of 1.68 MW.

39.1 μJ picosecond ultraviolet pulses at 355 nm with 1 MHz repeat rate

Based on our reliable high-power picosecond laser source with high beam qualities, we designed a compact and efficient third harmonic generation scheme by cascading a frequency doubling and a sum frequency generation using LBO as the nonlinear material. A maximum output of 39.1 W with a repeat rate of 1 MHz at 355 nm was obtained, which implied a pulse energy of 39.1 μJ, which was the highest picosecond UV pulse energy with an all-solid-state setup so far. The total conversion efficiency from infrared to UV was up to 46%. And the output UV has excellent beam qualities with an M-square factor less than 1.1.