Lianke Sun

Optimization of Cr/sup 4+/-doped saturable-absorber Q-switched lasers

Cr/sup 4+/-doped saturable absorbers are characterized by long excited state lifetime and appreciable excited state absorption. In the paper, we first solve the three coupled rate equations describing the operation of Cr/sup 4+/-doped saturable-absorber passively Q-switched lasers to obtain the expressions of pulse characteristics such as output energy, peak power, and pulsewidth. We then determine the key parameters of an optimally coupled passively Q-switched laser as functions of two variables concerning the amplifying medium, saturable-absorber medium, and pump level, and generate several design curves. These key parameters include the optimal normalized coupling parameter and the optimal normalized saturable-absorber parameter which maximize the output energy (or maximize the peak power, or minimize the pulsewidth), and the corresponding normalized energy, normalized peak power, and normalized pulsewidth. The results are valid for not only Cr/sup 4+/-doped saturable-absorber Q-switched lasers but also any other lasers passively Q-switched by saturable absorbers with long excited state lifetime and appreciable excited state absorption. Using the expressions and design curves, with the aid of a simple hand calculator, one can predict the pulse characteristics and perform the design of an optimally coupled passively Q-switched laser.

Laser diode pumped Cr4+:YAG passively Q-switched Nd3+:S-FAP laser

Abstract A laser diode pumped Cr 4+ :YAG repetitively and passively Q-switched Nd 3+ :S-FAP laser is studied theoretically and experimentally. The pulse energies, pulsewidths and pulse repetition rates in different conditions are measured and the experimental results are in agreement with the theoretical predictions on the whole.

Passively Q-switched self-frequency-doubled Nd 3+ :GdCa 4 O(BO 3 ) 3 laser

The performance of a flash-lamp-pumped self-frequency-doubled Nd3+:GdCa4O(BO3)3 (Nd:GdCOB) laser that is passively Q switched with Cr4+:YAG saturable absorbers is demonstrated. The maximum 0.53-µm pulse energy obtained is 2.6 mJ, and the maximum peak intensity is 15 MW/cm2. The dependence of the pulse characteristics on the orientation of the saturable absorber and on the cavity length is measured. Meanwhile, the transversal distribution of the intracavity photon density is taken into account in the rate equations for an intracavity frequency-doubled passively Q-switched laser, and the solutions are used to account for the behavior of the passively Q-switched Nd:GdCOB laser.

Growth and laser properties of Nd:Ca4YO(BO3)3 crystal

Abstract Nd:Ca 4 YO(BO 3 ) 3 (Nd:YCOB) crystal was grown by the Czochralski method, and its structure was measured by using a four circle X-ray diffractometer. The transparent spectrum from 200 to 2600 nm was measured at room temperature. The fluorescence spectrum near 1.06 μm showed that the main emission wavelength of Nd:YCOB crystal was centered at 1060.8 nm. Laser output at 1.06 μm has been demonstrated when it was pumped by a Ti:sapphire laser at the wavelength of 794 nm, the highest output power was 68 mW under pumping power of 311 mW, the pumping threshold was 163 mW and slope efficiency was 46.9%. The self-frequency doubled green light has been observed when it was pumped by a Ti:sapphire or a laser diode (LD). A 14.5 mm Nd:YCOB crystal sample cut at ( θ , φ )=(90°, 33°) was used for type I second-frequency generation (SHG) of the 1.06 μm laser pulse. The SHG conversion efficiency was 22%.

Growth and thermal properties of Yb:Ca4YO(BO3)3 crystal

Abstract Yb:Ca4YO(BO3)3 (Yb:YCOB) crystal of good quality and large size has been grown by the Czochralski method. The thermal expansion and specific heat have been measured. The thermal expansion coefficients along X, Y and Z axes are 12.0×10−6/K, 3.3×10−6/K and 6.6×10−6/K, respectively. The specific heat is 79.5 cal/mol K at 330 K.

Investigation of LD end-pumped Nd:YVO4 crystals with various doping levels and lengths

Abstract The absorption properties of Nd:YVO4 crystals with various doping levels and lengths are reported. The effective stimulated emission cross-sections of different doping levels are calculated with measured upper-level lifetimes. Our investigation gives good advice on the optimization of LD end-pumped Nd:YVO4 laser.

Diode-laser pumped Nd:Sr5(PO4)3F miniature green laser

By using a laser diode as the pump source and KTP as the intracavity doubling crystal, we have achieved green laser output at 0.5295 µm from a new crystal, Nd:Sr5(PO4)3F. The threshold power is 10 mW, and the TEM00-mode green laser output power is 40.4 mW at 400-mW incident pump power of the diode laser, corresponding to an optical efficiency of 10.1%. The theoretical formula for a cw intracavity frequency-doubled laser is given and is in agreement with the experimental result.

Laser demonstration of a diode-laser-pumped Nd:Sr5(PO4)3F crystal☆

Abstract The absorption spectrum of a new crystal Nd:Sr5(PO4)3F (Nd:S-FAP) was measured and its strong absorption peak at 805.4 nm showed that it can be suitably pumped with a laser-diode. By using a laser-diode pump operating at 805.4 nm, Nd:S-FAP has been successfully lased at 1.059 μm. A slope efficiency of 37.5% and a laser threshold of only 13 mW have been measured, and the theoretical prediction is in agreement with the experimental result.

Passively Q-switched self-frequency doubling NdxY1-xAl3(BO3)4 laser with Cr4+ :YAG saturable absorber

Abstract Using a new saturable absorber Cr4+:YAG as passive Q-switch, we have realized the Q-switched laser running at 0.531 μm with an NYAB self-frequency doubling crystal and measured the single pulse energy and the pulse width under different small-signal transmissions of Cr4+:YAG and different cavity lengths. Meanwhile, the coupling wave rate equations for Cr4+:YAG as a passive Q-switch are given and the experimental results agree with the numerical solution of equations.

Diode-laser-pumped passively Q-switched Nd:S-FAP green laser

By using a laser-diode as pump source and saturable absorber Cr4+:YAG as passive Q-switch, a KTP as intracavity frequency doubling crystal, we have realized green Q- switched laser output at 0.5295 micrometers from a Nd:S-FAP crystal. The output green laser characteristics, such as the average power, the single pulse energy, the pulse width, the repetition rate for different small-signal transmission of Cr4+:YAG and different pump power, were measured. Meanwhile, the coupling rate equations of intracavity frequency doubling for Cr4+:YAG as passive Q-switch were given and the numerical solution of equations agreed with the experimental results.