Jingang Liu

Influence of the thermal effect on the TEM 00 mode output power of a laser-diode side-pumped solid-state laser

A fraction of pump power has been converted to TEM00 mode laser power for a side-pumped solid-state laser by use of a space-dependent rate equation. We investigated the pump-to-mode (TEM00) ratio when scaling laser-diode side-pumped solid-state lasers to high-power levels by including the thermal effect in the space-dependent rate equation. Based on the assumption that Gaussian pump power is the same at any cross section of a laser rod, we resolved the output power with a space-dependent rate equation; temperature distribution in the laser rod was obtained; the optical path difference distribution was derived, and we estimated the diffraction losses that result from thermally induced spherical aberration by use of the Strehl intensity ratio. We determined that thermally induced diffraction losses are strongly dependent on pump power and on the pump-to-mode ratio.

Modeling pulse shape of Q-switched lasers

A general approach describing the pulse shape and temporal width of Q-switched lasers has been derived. Based on a normalized intermediate variable describing the ratio of population inversion density at the beginning of Q-switch to that at threshold, a generalized characteristic equation that governs passively and actively Q-switched lasers is derived. From the characteristic equation, the pulse symmetry property and pulse width can be described and easily calculated for any given operating parameters, and the waveform of the laser pulse can be reconstructed without solving the laser rate equations. An approach is also given for the case of intracavity frequency-doubled Q-switched lasers. Theoretical results show agreement with experiments for a diode pumped Nd:YAG laser system that is passively Q-switched by a Cr/sup 4+/:YAG absorber.

Thermal lensing of diode side-pumped solid-state lasers

The pump energy distribution in a diode side-pumped solid-state laser, is an overlap of propagating Gaussian beams. A simple model has been developed to calculate the thermal focal length of a diode side-pumped solid-state laser, which is based on a thermal model with a Gaussian heat density in any cross section of a laser rod. It can be seen that as the waists of pump beams increase, the energy distribution tends to be uniform and the thermal focal length tends to be long, which means a smaller thermal focusing.

Thermal and optical properties of diode side-pumped solid state laser rods

Thermal heating is a major limiting factor in scaling the average power of a solid-state laser. The relationship between the heat intensity in a laser slab and the heat transfer coefficient has been studied by considering the variations of thermal conductivity and expansion coefficient of the laser slab with temperature. In this paper, the laser rod has been studied by including its thermal, stress and optical aberration effects. It is pointed out that different heat transfer coefficients should be adopted according to different heat intensities inside the laser rod in order to obtain better pumping input as well as to optimize the cooling effects.

Generation of passively Q-switched and mode-locked pulses from a Nd:YAG laser with a GaAs output coupler

Passively Q-switching and mode-locking has been realized in a diode-pumped Nd:YAG laser using a GaAs wafer as an output coupler as well as a saturable absorber. The laser has a Z-type cavity to achieve a tight-focused beam at the saturable absorber and to realize an optimum mode matching in the laser crystal simultaneously. At an incident pump power of 13.8 W, the average output power was 1.62 W. The repetition rate and pulse width of the Q-switched pulses are in the range of 29 to approximately 73 kHz and 0.73 to approximately 1.87 microsecond(s) , respectively. The mode-locked pulses were measured to have a repetition rate of 154 MHz and an average pulse duration of 42 ps.

Characteristics of heat transfer for diode-pumped solid state lasers

The relationship between heat effect and the convective heat transfer coefficient using analytical heat transfer equations is studied. We point out that different convective heat transfer coefficients should be adopted according to different heat densities inside the laser crystal in order to obtain better pumping input as well as cooling effect.

Investigation on the use of semiconductor as Q-switch as well as output coupler for diode-pumped solid-state lasers

Summary form only given. Passive Q-switching has attracted much research attention in recent years, especially for diode-pumped solid-state lasers. In the previous work, we demonstrated passive Q-switching using undoped and uncoated GaAs wafers as Q-switch elements as well as output couplers for several laser systems. This kind of Q-switching has the advantages of lowering cost, shortening laser cavity, simplifying the laser operation, and improving the compactness of laser system. In this paper, we reported more detailed studies of the transmissivity and saturable absorption, and the passive Q-switching performance using several different GaAs wafers.

Theoretical analysis and simulation of a hybrid diode-pumped solid state laser

In this paper, a symmetrical optical resonator that contains the dual-telescopic elements and two rods used for a hybrid diode end-pumped and side-pumped geometry is investigated theoretically to generate high scaling laser output. The dual telescopes within resonators are appropriately chosen and adjusted to achieve a large-volume TEMoo mode and to minimize the effects of the variations of the focal length in the rod. The movement of the optimal operation point of resonator caused by larger change range of pump power will be compensated by adjusting telescope defocusing. The resonator can also be applied for diode-pumped high-average- power solid-state lasers.

Femtosecond Self-Mode-Locked La1-xMgNdxAl11O19 Laser Pumped by a Laser Diode

A laser-diode-pumped self-mode-locked La1-xMgNdxAl11O19 laser has been demonstrated. Transform-limited pulses of 631 fs duration have been generated from the laser, which corresponds to a spectral width of 2.03 nm. The time-bandwidth product and average output power were 0.34 and 11 mW, respectively. Characteristic parameters of the LNA laser, such as the stability, the strength of the self-mode-locking, and the change of beam spot size with intracavity normalized power have been calculated and optimized. The theoretical simulation results are in good agreement with the experiments.

Model for fabricating close-coupling pumped microchip lasers

We present a general model for design and fabrication of high efficient, high brightness IR and visible microchip lasers closely coupling pumped by a fiber coupled diode laser. The design parameters and the output laser characteristics are simulated for both cw and Q-switch operations, as well as their wavelength conversions.