Q-switched Yb 3+ :YVO 4 laser with Raman self-conversion

We report the efficient continuous-wave (CW) and Q-switched laser operation of a diode-pumped Yb:YVO₄ laser. A CW output power of 1 W with a slope efficiency of 59% with respect to absorbed pump power was demonstrated. Passively Q-switched with a Cr⁴⁺:YAG saturable absorber, a Yb:YVO₄ laser with Raman conversion was demonstrated. Q-switched 18.7- J pulses with a pulse duration of 17 ns and a peak power up to 1 kW were obtained at 1018-nm fundamental wavelength and 3.6- J pulses with a pulse duration of 6 ns and a peak power of about 0.6 kW were obtained at 1119.5-nm first-Stokes wavelength.This revised version was published online in March 2005. In the previous version, the published online date was missing     

Emission properties of a Tm30.1mm+:GdVO4 microchip laser at 1.9 μm

4 as a host for thulium has several advantages for diode pumping in comparison with other crystals. The absorption cross section of thulium in GdVO₄ is considerably stronger and broader than in YAG and YLF and the spectrum is shifted closer to the emission wavelength of commercially available AlGaAs laser diodes. In our paper, we report on the temporal and spectral emission properties of a monolithical Tm^30.01mm+([%at.]6.9):GdVO₄ microchip laser at 1.9 μm. The laser can be adjusted to emit either cw or in an oscillating regime. Slope efficiencies up to 47% are achieved. This value exceeds the Stokes limit of 42%. Received: 31 March 1998/Revised version: 02 June 1998     

Excited-state absorption in Er: BaY2F8 and Cs3Er2Br9 and comparison with Er: LiYF4

The influence of Excited-State Absorption (ESA) on the green laser transition and the overlap of Ground-State Absorption (GSA) and ESA for 970 nm upconversion pumping in erbium is investigated in Er³⁺ : BaY₂F₈ and Cs₃Er₂Br₉. Results are compared to Er³⁺ : LiYF₄. In Er³⁺: BaY₂F₈, a good overlap between GSA and ESA is found at 969 nm in one polarization direction. The emission cross section at 550 nm is a factor of two smaller than in LiYF₄. In Cs₃Er₂Br₉, the smaller Stark splitting of the levels shifts the wavelengths of the green emission and ESA from⁴ I _{1 3/2} off resonance. It enhances, however, ground-state reabsorption. The emission cross section at 550 nm is comparable to LiYF₄. Upconversion leads to significant green fluorescence from² H _9/2. A significant population of the⁴ I _11/2 level and ESA at 970 nm are not present under 800 nm pumping.     

Output power optimisation of slab-waveguide laser with Gaussian output mirror

We present an approximate analysis of the nonlinear operation of the hollow slab-waveguide laser with Gaussian reflectivity profile output mirror, including gain saturation and longitudinal as well as transverse field distribution of the laser mode. The model presented is general and can be applied to the study of arbitrary configuration of the slab-waveguide laser. In particular, the laser characteristics obtained reveal the influence of the position of the output mirror and the Gaussian mirror parameter on the power efficiency of the laser system. Received: 6 January 2000 / Published online: 8 November 2000     

Copper-vapour laser with silver additive

Results of experimental investigation of a pure elemental copper-vapour laser with silver additive are reported. Average output power as well laser output pulse energy increased by up to 10% with the additive. A possible mechanism of additive influence on laser output parameters is discussed.     

High-average-power flashlamp-pumped Nd:Glass fiber-bundle laser

Flashlamp-pumped high-gain fiber-bundle lasers consisting of multimode phosphate glass fibers have been investigated. By optimizing the fiber number and the outcoupling reflectivity in dependence on the pump conditions, high single-pulse energies in excess of 1 J as well as high-average-power extraction up to 100 W at a pulse repetition frequency of 100 Hz could be obtained from slim fiber-bundle lasers. Fiber numbers in the range of 150–250 and reflectivities between 35% and 50% have been found to provide reliable performance.     

Continuous wave diode pumped Yb:LLF and Yb:NYF lasers

Experimental and theoretical results of investigation of CW Yb:LiLuF₄ (Yb:LLF) and Yb:Na₄Y₆F₂₂ (Yb:NYF) lasers under longitudinal diode laser pump are reported. Slope efficiencies of 41%, 58% with 0.21, 0.53 W of output powers were obtained for the Yb:LLF and Yb:NYF lasers, correspondingly. The Yb:NYF laser demonstrated tunability in the region from 1005 to 1061 nm. The mathematical modelling of CW laser operation predicts under optimized laser parameters optical to optical efficiencies of about 55% and 51% for Yb:LLF and Yb:NYF lasers, respectively.     

A flashlamp-pumped 946 nm Nd:YAG laser

Generation of 946 nm radiation from a commercially available, flashlamp-pumped Nd:YAG laser was investigated. By suppression of the high-gain 1.064 m transition and with a specially designed cooling system, a stable emission at 946 nm was achieved in the temperature range 300–240 K. At a repetition rate of 10 Hz laser output powers of 100mW and 500 mW were obtained at room temperature and 240 K respectively. The temperature dependence of unsaturated gain, slope efficiency and pumping threshold were determined.S. Dimov is supported by a fellowship from the Alexander von Humboldt Foundation     

High-power diode-end-pumped Nd:YVO4 laser: thermally induced fracture versus pump-wavelength sensitivity

We report two kinds of compact and efficient diode-end-pumped TEM₀₀ lasers with output power >25 W at ≈50 W of incident pump power. One laser consists of a single 0.3 at. % Nd:YVO₄ crystal in a V-type cavity, the other laser includes two 0.5 at. % Nd:YVO₄ crystals in a linear cavity. Experimental results show that lowering Nd³⁺ concentration can be beneficial in extending the fracture-limited pump power but it also increases the sensitivity of the pump wavelength due to the overlapping efficiency. Received: 19 February 2000 / Revised version: 30 May 2000 / Published online: 20 September 2000     

Efficient passively Q-switched operation of a diode-pumped Nd:GGG laser with a Cr:YAG saturable absorber

The continuous-wave (cw) and passive Q-switching operation of a diode-end-pumped gadolinium gallium garnet doped with neodymium (Nd:GGG) laser at 1062 nm was realized. A maximum cw output power of 6.9 W was obtained. The corresponding optical conversion efficiency was 50.9%, and the slope efficiency was determined to be 51.4%. By using Cr⁴⁺:YAG crystals as saturable absorbers, Q-switching pulse with average output power of 1.28 W, pulse width of 4 ns and repetition rate of 6.2 kHz were obtained. The single-pulse energy and peak power were estimated to be 206 μJ and 51.6 kW, respectively. The conversion efficiency of the output power from cw to Q-switching operation was as high as 84.7%.     

On the performance of short pulse Nd3+:LSB microchip lasers

Experimental results from studies of the laser characteristics of Nd:LSB crystals in both cw and passive Q-switching arrangements are presented. The dependence of the main laser parameters on the output coupling and saturable absorber transmission for two doping levels of Nd was investigated. It is demonstrated that due to its high absorption, low losses and intrinsic strong thermal lensing, even at pump powers of less than 200 mW, the Nd:LSB has excellent properties in terms of efficiency, beam quality and pulse duration. In addition, it exhibits high pulse-to-pulse and pulse width versus pump power stability. Received: 11 June 2001 / Revised version: 30 July 2001 / Published online: 15 October 2001     

High-power Nd:YAG planar waveguide laser with YAG and Al2O3 claddings

Thermal effects in Nd:YAG planar waveguide lasers with non-symmetrical claddings are discussed. The heat generated in the active core can be removed more efficiently by directly contacting the active core to the heat sink. Several cladding materials are compared to optimize the heat removal. Furthermore, uniform pumping is achieved with oblique edge-pumping technique. Using quasi-CW pumping at 1 KHz repetition rate, an average output power of 280 W with a slope efficiency of 38% is obtained with a positive unstable resonator.     

Additive-pulse mode locking of a diode-pumped Nd3+:YVO4 laser

We demonstrate self-starting additive-pulse mode locking of a diode-pumped Nd³⁺:YVO₄ laser. Pulse durations of 2.7 ps are measured at a repetition frequency of 90.7 MHz and at an average output power of 1.1 W. This corresponds to a peak power of 4.5 kW. Received: 27 June 2001 / Revised version: 10 October 2001 / Published online: 29 November 2001     

Self-Q-switched and mode-locked Nd,Cr:YAG laser with 6.52-W average output power

Simultaneous self-Q-switched and mode-locked have been demonstrated in a diode-pumped Nd,Cr:YAG laser. For the first time as we know, almost 100% modulation depth has been achieved at an intracavity intensity of 5.6 × 10⁵ W/cm². The maximum average output power of 6.52 W corresponding to a slope efficiency of 30% is obtained at 1064 nm. The laser produces high-quality pulses in a TEM₀₀-mode at the pump power of 16.5 W. The pulse duration of the mode-locked pulses is about 600 ps with 136 MHz repetition rate.     

Thermal effects investigation and cavity design in passively mode-locked Nd:YVO4 laser with a SESAM

A diode-pumped passively mode-locked Nd:YVO₄ laser with a five-mirror folded cavity is presented by using a semiconductor saturable absorber mirror (SESAM). The temperature distribution and thermal lensing in laser medium are numerically analyzed to design a special cavity which can keep the power density on SESAM under its damage threshold. Both the Q-switched and continuous-wave mode-locked operation are experimentally realized. The maximum average output power of 8.94 W with a 9.3 ps pulse width at a repetition rate of 111 MHz is obtained under a pump power of 24 W, correspondingly the optical slope efficiency is 39.2%.     

Solid-state active media of tunable organic- compound lasers pumped with a laser. II. A copper vapor laser

The lasing properties of organic compounds in a polymethylmethacrylate matrix pumped by a copper vapor laser are studied. The results demonstrate that the transverse pumping scheme of solid-state laser-active media with the copper vapor laser is promising compared to the longitudinal pumping scheme from the viewpoint of the lifetime parameters. Received: 6 February 2002 / Published online: 2 May 2002     

Continuous-wave broadly tunable Cr:ZnSe laser pumped by a thulium fiber laser

We describe a compact, broadly tunable, continuous-wave (cw) Cr²⁺:ZnSe laser pumped by a thulium fiber laser at 1800 nm. In the experiments, a polycrystalline ZnSe sample with a chromium concentration of 9.5 × 10¹⁸ cm⁻³ was used. Free-running laser output was around 2500 nm. Output couplers with transmissions of 3%, 6%, and 15% were used to characterize the power performance of the laser. Best power performance was obtained with a 15% transmitting output coupler. In this case, as high as 640 mW of output power was obtained with 2.5 W of pump power at a wavelength of 2480 nm. The stimulated emission cross-section values determined from laser threshold data and emission measurements were in good agreement. Finally, broad, continuous tuning of the laser was demonstrated between 2240 and 2900 nm by using an intracavity Brewster cut MgF₂ prism and a single set of optics.     

Specialty Yb fiber amplifier for microchip Nd laser: Towards ∼1-mJ/1-ns output at kHz-range repetition rate

We demonstrate and optimize, for a mJ/ns release at the wavelength 1.064 μm, the operation of a compact laser system designed in the form of a hybrid, active-passive, Q-switched Nd³⁺:YAG/Cr⁴⁺:YAG microchip laser seeding an Yb-doped specialty multi-port fiber amplifier. As the result of the amplifier optimization, ∼1 mJ, ∼1 ns, almost single-mode pulses at a 1-10-kHz repetition rate are achieved, given by a gain factor of ∼19 dB for an 11-μJ input from the microchip laser. Meanwhile, a lower pulse energy, ∼120 μJ, but a much higher gain (∼25 dB) are eligible for the less powerful (0.35 μJ) input pulses.     

Diode-pumped passively Q-switched Nd:GdVO4 laser at 1342 nm with V:YAG saturable absorber

We have demonstrated an efficient diode-pumped passively Q-switched Nd:GdVO₄ laser working at 1342 nm by using an uncoated V³⁺:YAG crystal as the saturable absorber, in which both a-cut and c-cut Nd:GdVO₄ crystals are employed. At the maximum absorbed pump power of 9.45 W, the maximum average output power can reach 519 mW and 441 mW corresponding to the output coupler with different transmission of 3% and 10% by using an a-cut Nd:GdVO₄ crystal at 1342 nm, while the shortest pulse duration could be as low as 21.7 ns and 22.3 ns with the repetition rate of 48.41 kHz and 53.25 kHz by using a c-cut Nd:GdVO₄ crystal, corresponding to the output coupler with different transmission of 3% and 10% at 1342 nm, and the single Q-switched pulse energy are 6.67 uJ and 7.06 uJ, the pulse peak power are 307 W and 316 W, respectively. The experimental results show that c-cut Nd:GdVO₄ laser can generate shorter pulse with higher peak power in comparison with a-cut one.     

Pulse compression in AO Q-switched diode-pumped Nd:GdVO4 laser with Cr4+:YAG saturable absorber

By simultaneously using both an acoustic-optic (AO) modulator and a Cr⁴⁺:YAG saturable absorber in the cavity, for the first time, a diode-pumped doubly Q-switched Nd:GdVO₄ laser has been realized. The pulse duration is obviously compressed in contrast to the actively acoustic-optic Q-switched laser. By considering the Gaussian transversal distribution of the intracavity photon density and the longitudinal distribution of the photon density along the cavity axis as well as the influence of turnoff time of the acoustic-optic (AO) Q-switch, we provide the coupled rate equations for a diode-pumped doubly Q-switched Nd:GdVO₄ laser with both an acoustic-optic (AO) modulator and a Cr⁴⁺:YAG saturable absorber. These coupled rate equations are solved numerically, and the dependence of pulse width, pulse energy and peak power on the incident pump power at different pulse repetition rates is obtained. The numerical solutions of equations agree well with the experimental results.This revised version was published online in August 2005 with a corrected cover date.