Bernd Ozygus

Modeling of passively Q-switched lasers

The intracavity photon density and the initial population-inversion density in the diode-pumped passively Q-switched laser rate equations are assumed to be Gaussian spatial distributions. These space-dependent rate equations are solved numerically, and a group of general curves are generated. These curves clearly show the dependence of the pulse characteristics on the pump- to laser-mode size ratio and the parameters of the gain medium, the saturable absorber, and the resonator. They can also be used to estimate the pulse parameters of an arbitrary diode-pumped passively Q-switched laser and to determine the optimal pump- to laser-mode size ratio. In addition, these curves are not limited to diode-pumped lasers. Sample calculations for a diode-pumped Nd3+:YVO4 laser and a flash-lamp pumped Nd3+:YAG laser are presented to demonstrate the use of the curves and the related formulas.

Improvement of passive Q-switching performance reached with a new Nd-doped mixed vanadate crystal Nd:Gd0.64Y0.36VO4.

Passive Q-switching performance was found to be greatly improved by use of a new Nd-doped mixed vanadate crystal Nd:Gd0.64Y0.36VO4 compared with that achieved with Nd:YVO4 and Nd:GdVO4. At an absorbed pump power of 12 W, an average output power of 2.78 W was obtained at a pulse repetition frequency of 15.4 kHz with an optical conversion efficiency of 23.2%, and the slope efficiency was determined to be 45.5%. The resulting pulse energy, peak power, and pulse width were 181 microJ, 26.6 kW, and 6.8 ns, respectively.

Efficient passive Q-switching operation of a diode-pumped Nd:GdVO 4 laser with a Cr 4+ :YAG saturable absorber

A diode-pumped highly efficient Cr4+:YAG passively Q-switched Nd:GdVO4 laser formed by a plano–concave resonator has been demonstrated. At the highest attainable absorbed pump power of 11.4 W, 4.05 W of average output power, which was two thirds of the maximum corresponding cw output, was achieved with an optical conversion efficiency of 35.5%, and the slope efficiency was determined to be 46.8%, reaching 85% of the magnitude of its cw counterpart. The resulting shortest pulse duration, single-pulse energy, and peak power were found to be 13 ns, 90 μJ, and 7 kW, respectively, with a pulse repetition frequency (PRF) of 45 kHz. Two particularly modified resonator configurations were employed; the largest pulse energy and the highest peak power reached were, respectively, 154 μJ and 11.2 kW at 8.5 W of absorbed pump power. An analytical relation between the PRF and the absorbed pump power is given for a passively Q-switched laser, showing good consistency with experiment with a Nd:GdVO4 laser. The dependence of the operational parameters on the pump power and on the output coupling was also investigated experimentally. Issues involving the criterion for passive Q switching are discussed in some detail for Cr4+:YAG passively Q-switched neodymium-doped vanadate lasers.

Pulse energy enhancement in passive Q-switching operation with a class of Nd:GdxY1−xVO4 crystals

Passive Q-switching operation with a class of Nd:GdxY1−xVO4 crystals has been demonstrated. Compared to Nd:YVO4 and Nd:GdVO4, the pulse energy produced with Nd:Gd0.64Y0.36VO4 under certain conditions was found to be enhanced by factors of 6.0 and 2.5, while the peak power enhanced by factors of 14.7 and 3.6, respectively. At the incident pump power of 9.6 W, 1.3 W of average output power was obtained, with the pulse energy, peak power, and pulse repetition frequency being 166 μJ, 24.5 kW, and 7.7 kHz, respectively.

Modeling of diode-pumped actively Q-switched lasers

The intracavity photon density and initial population inversion density in the diode-pumped actively Q-switched laser rate equations are assumed to be Gaussian distributions. These space-dependent rate equations are solved numerically and a group of general curves are generated. By using these curves and the related formulas, the pulse parameters of an arbitrary actively Q-switched laser can be easily estimated and an optimally coupled Q-switched laser can be designed. A sample calculation for a Q-switched Nd/sup 3+/:YVO/sub 4/ laser is presented to demonstrate the use of the curves and the related formulas.

Degenerated confocal resonator

The properties of confocal resonators with g(1) = g(2) = 0 and with one mirror confined by an aperture were investigated both theoretically and experimentally. The fundamental mode operation with complete filling of the medium, which ds located near the unconfined mirror, can always be obtained by an appropriate choice of the aperture radius. Numerical calculations based on Fresnel integrals, including the amplification of the gain medium, provide a detailed understanding of the resonator properties, with guidelines for an optimum resonator performance. Diffraction loss, mode structure, beam quality, extraction efficiency, and misalignment sensitivity of these resonators are measured with a pulsed Nd:YAG laser in a single-shot operation.

Gain-induced coupling of solid-state lasers

Abstract In this paper a theoretical model is presented which describes the coherent coupling of two laser modes inside the same crystal. The modes are pumped independently by two fibre-coupled laser diodes. The theoretical predictions of various locking effects are compared with first experimental results. Different phase-locking states and frequency locking are observed.

Diode-pumped cw and Q-switched Nd:GdVO4 laser operating at 1.34 μm

A diode-pumped 1.34 μm Nd:GdVO4 laser operating in cw and active Q-switching modes has been demonstrated. 4.15 W of cw output power was obtained at the highest attainable pump power of 12.3 W, resulting in an optical conversion efficiency of 33.7%, the slope efficiency was determined to be 37.6%. In Q-switching operation, a maximum average output power of 2.7 W was generated at pulse repetition frequency (PRF) of 50 kHz, with an optical conversion efficiency of 22% and a slope efficiency of 29.2%. The laser pulses with shortest duration, highest energy and peak power were achieved at PRF of 10 kHz, the parameters being 15 ns, 160 μJ, and 10.7 kW, respectively. By intracavity frequency-doubling with a type II phased-matched KTP crystal, 0.62 W average power at 0.67 μm was produced at a PRF of 15 kHz, the resulting pulse energy, peak power, and pulse width being 41.3 μJ, 2.2 kW, and 19 ns, respectively. A group of analytical formulae, based on rate equations, are presented to evaluate the operational parameters of an actively Q-switched laser. Calculated results were found to be in close consistency with the experimental data.

Diode-pumped multipath laser oscillators

Multipath resonators are well known as optical delay lines. By many zick-zack rays between two mirrors large optical path lengths can be obtained. This passive system can be converted into a laser oscillator by closed ray paths and a Nd:YAG crystal at one mirror. Optical pumping occurs by directly coupled diodes at the reflection points. Very efficient (more than 40% optical/optical) and compact systems up to 20 W, with the beam propagation factor m2 < 3 were generated. Q-switching and internal frequency doubling were also demonstrated. The fundamental physics of this system including the transverse mode-locking at the degeneration points of the resonator was investigated, experimentally and theoretically.

Rate equations and their solutions of laser-diode-pumped repetitively passively Q-switched lasers by taking into account the spatial variation of pumping and intracavity photon density

This paper presents the experimental results of a CW laser- diode end-pumped passively Q-switched Nd3+:YAG laser with a Cr4+:YAG saturable absorber and two groups of theoretical results. The first group is obtained by numerically solving the passively Q-switched laser rate equations in which the spatial variation of pumping and intracavity laser intensity is taken into account. The second group is obtained from the analytical solutions of Q- switched laser rate equations under the plane-wave approximation. The comparison shows that the first group is more close to the experimental results.