Waldemar Zendzian

Q-switched mode locking with acousto-optic modulator in a diode-pumped Nd:YVO4 laser.

The Q-Switched Mode Locking (QML) regime provides the generation of relatively high peak power picosecond pulses train with energies of a few muJ each in a simple resonator. The fully modulated efficient QML regime was demonstrated in the diode-pumped Nd:YVO4 laser. The acousto-optic cell playing a double role of Q-switch and Mode Locker was located near flat output coupler. The two folding mirrors were mounted on the translation stages for matching the resonance frequency of the cavity to the radio frequency of acousto-optic modulator. The QML pulses with envelope durations of 100-150 ns and near 100% modulation depth were observed for wide range of pump powers and repetition rates. Up to 3 W of output average power, 100 muJ of the envelope energy, having approximately 5-8 mode-locked pulses were achieved.

250 mJ, self-adaptive, diode-side-pumped Nd:YAG slab laser

A scheme of self-adaptive, closed-loop, diode-side-pumped Nd:YAG slab laser was presented. As a result of four-wave mixing of standing waves intersecting at a small angle in a closed-loop cavity, the self-adaptive process of beam cleaning leading to fundamental mode operation despite severe asymmetry of the inversion profile and thermal-optical distortion was achieved. The output beam was extracted from the cavity as the first- order diffraction beam on the dynamic gain gratings created in an active medium. The near-diffraction-limited (parameter M(2)<1.4, divergence of 1 mrad) output beam of 250 mJ energy and the optical slope efficiency of 30% at a repetition rate of up to 25 Hz in a free-running regime were demonstrated.

Resonantly pumped, high peak power Er:YAG laser

The high peak power hybrid Er:YAG laser, resonantly pumped at the wavelength of 1532 nm was developed. The fused silica acousto-optic modulator driven by 10 W of RF power was deployed as the Q-switch for such a laser. For the best case of Q-switching regime the pulses of 110 kW peak power (4 mJ, 37 ns) were reached at the pump power of 7.8 W and the repetition rate of 500 Hz.

Chromium-doped LiCAF laser passively Q switched with a V 3+ :YAG crystal

A tunable, lamp-pumped Cr3+:LiCaAlF6 laser that operates in the 760-800-nm wavelength range is demonstrated. As a passive Q switch the V3+:YAG crystal, characterized by wide saturable absorption in the 760-900-nm wavelength range, was applied. The V3+:YAG parameters were determined by spectroscopic and saturable transmission measurements. The 30-mJ output energy at 2-Hz repetition rate in the free-running regime was obtained in a cavity reinforced by a diaphragm near the fundamental mode. The dispersive prism inserted into the cavity enabled tuning in the 760-800-nm wavelength range. In the passive Q-switching regime we achieved greater than 1-mJ energy with 50-ns pulse duration in a 35-cm-long cavity. A numerical model that takes into account the short recovery time of V3+:YAG (approximately 5 ns) and excited-state absorption was used to analyze such a laser.

Q-switched Er:YAG lasers resonantly pumped by Erbium fiber laser

The study describes efficient, acousto-optic Q-switching of Er:YAG laser at the 1645 nm eye-safe wavelength. For longitudinal pumping at wavelength 1532 nm, linear-polarized 10 W Erbium fiber laser radiation was used. The investigated Er:YAG crystals were 25 and 40 mm long and their Erbium concentration was 0.20 and 0.25%, respectively. For giant pulse generation, a fused silica acousto-optic modulator was inserted inside the Er:YAG laser oscillator. For a maximum incident pump power of 7.95 W, pulse energy up to 4.1 mJ was generated with pulse duration 34 ns at 500-Hz repetition rate; the corresponding peak power was 119 kW.

Pulsed 1.645 μm Er3+:YAG laser with increased average output power and diffraction limited beam quality

An actively Q-switched Er 3C :YAG laser operating at the wavelength of 1645 nm was developed. The system was TIR (total internal reflection), resonantly diode-pumped at the wavelength of 1532 nm with a repetition rate of 100 Hz. For 305 mJ of incident pump pulse energy, output pulse energy of 24 mJ was generated with almost 8% of optical-to-optical efficiency. At maximum pumping power the M 2 parameter of the generated beam was 1. (Some figures may appear in colour only in the online journal)

Optimization of end-pumped, actively Q-switched quasi-III-level lasers

The new model of end-pumped quasi-III-level laser considering transient pumping processes, ground-state-depletion and up-conversion effects was developed. The model consists of two parts: pumping stage and Q-switched part, which can be separated in a case of active Q-switching regime. For pumping stage the semi-analytical model was developed, enabling the calculations for final occupation of upper laser level for given pump power and duration, spatial profile of pump beam, length and dopant level of gain medium. For quasi-stationary inversion, the optimization procedure of Q-switching regime based on Lagrange multiplier technique was developed. The new approach for optimization of CW regime of quasi-three-level lasers was developed to optimize the Q-switched lasers operating with high repetition rates. Both methods of optimizations enable calculation of optimal absorbance of gain medium and output losses for given pump rate.

Acousto-optic modulation in diode-pumped solid-state lasers

The main properties of acousto-optic modulators (AOMs) applied in laser technology are presented and discussed. The critical review of application of AOMs in several types of diode-pumped solid-state lasers (DPSSLs) is given. A short description of few DPSSLs developed in our group is presented. The parameters of a simple AO Q-switched Nd:YVO 4 laser (peak power up to 60 kW, pulse duration 5 to 15 ns, repetition rate 10 to 100 kHz, with average power above 5 W) are satisfactory for various applications. The achieved brightness of 10 17 W/m 2 /sr is comparable to that of the strongest technological Q-switched lasers of kilowatt average power. The main aim of paper is to present novel type of laser with acousto-optic modulation, namely, the AO Q-switched and mode locked (QML) laser. We have designed a 3.69-m-long Z-type cavity with resonance frequency matched to the rf of the AOM. As a gain medium an Nd:YVO 4 crystal end-pumped by a 20-W laser diode was applied. The envelope energy of the QML pulse train was up to 130 μJ with subnanosecond mode-locked pulses of 30-μJ maximum energy.

Modeling of beam width in passively Q-switched end-pumped lasers

An iterative model based on the LambertW function was developed for estimating the fundamental mode parameters of resonators with saturable gain guiding. The process of pulse buildup in passively Qswitched, end-pumped lasers was analyzed. The effective ABCD cavity matrix for consecutive round-trips was calculated, taking into account spatially variable saturated gain in an active medium and absorption bleaching in a saturable absorber. The twofold decrease in beam width, as compared with the fundamental mode of the bare cavity, was demonstrated. The application of such a model for resonators with other nonlinear elements is feasible.

Comparison of diode-side-pumped triangular Nd:YAG and Nd:YAP laser

Nd:YAG and Nd:YAP slab crystal in the form of triangle with the Brewster-angle-cut polished input faces was used as an active medium for diode-side-pumped laser. A horizontal projection of the active medium form is a triangle with 19.22 mm long base, 5 mm height, and thickness of 4 mm. This active crystal shape is one from the simplest form which makes possible to realise a slab side-pumped configuration with a total internal reflection. Optical pumping was accomplished by a quasi-cw diode ARR18P400 with peak power 400 W closely attached to the active crystal without any coupling optics. Both material were operated for most known Nd3+ ion transition 4F3/2→4I11/2 (1 μm) as well as for transition 4F3/2→4I13/2 which leads to the emission at 1.3 μm. The systems were tested in free running and Q switch regime. This system is enough compact to be useful tools for direct medical application.