YAG Saturable Absorber Research Articles

Repetition rate control in continuous-wave-pumped, passively Q-switched solid-state lasers

We describe a technique for the adjustment and control of repetition rates in continuous-wave-pumped, passively Q-switched solid-state lasers. The method uses a movable intracavity lens to modify the mode matching and hence the gain of the laser beam per pass. The technique was applied to a diode-pumped Nd3+:YVO4 laser passively Q-switched with a Cr4+:YAG saturable absorber at 1064 nm. At a fixed pump power of 5.4 W, we were able to continuously adjust the repetition rate between 13.8 and 25 kHz by translating an intracavity converging lens. We also demonstrate that by adjusting the lens position, the repetition rate can be kept at a desired value as the pump power varies. In particular, as the pump power was increased from 3.95 to 5.9 W, the lens position was varied by 0.91 cm to keep the repetition rate constant at 13.8 kHz. Rate-equation formalism was used to investigate the variation of the repetition rate as a function of lens position, and very good agreement was obtained between experiment and theory.

Saturation of 1047- and 1064-nm Absorption in ${\hbox {Cr}}^{4+}$:YAG Crystals

To investigate the physical mechanism of the saturation process in Cr4+:YAG crystals we solved the three coupled rate equations which describe the saturable absorber. We experimentally verified this model using two lasers with nanosecond pulses and continuous-wave radiation. We used crystalline and ceramic Cr4+-doped YAG saturable absorbers with various initial transmissions. The ratio between the ground and the excited-state absorption cross section at 1064 nm was measured to be between 3.8 plusmn 0.2 and 4.7 plusmn 0.2 for crystalline and 3.6 plusmn 0.1 for ceramic Cr4+:YAG. The ratio between the above named cross sections at 1047 nm was found to be 6.2 plusmn 0.2 for both crystalline and ceramic Cr4+:YAG. With these results the ground-state and the excited-state absorption cross sections at 1047 nm were calculated to be (9.55plusmn0.01)times10-19 cm2 and (1.54plusmn0.03)times10-19 cm2, respectively

Computational model for simultaneous Q switching and mode-locking in a solid state laser with a saturable absorber

A numerical model of rate equations for a four-level solid state laser with Cr4+:YAG saturable absorber including excited state absorption ESA is presented. The cavity is divided into a large number of disks and the model is solved for each disk and its local corresponding photon flux. The flux array is shifted for each recurrence simulating the movement of photons inside the cavity during the round trip. This simulator can describe the mode-locking phenomenon and can be used to simulate simultaneous mode locking and Q switching with a saturable absorber.

Nd:YAG/V:YAG monolithic microchip laser operating at 1.3 μm

Two longitudinally diode-pumped Nd:YAG/V:YAG Q-switched microchip lasers emitting radiation at wavelength 1.3μm were realized. The first laser, designed for higher pump power, was based on the composite crystal which combines in one piece a 4mm long cooling undoped YAG crystal, 12mm long Nd:YAG laser active part, and 0.7mm long V:YAG saturable absorber. The second one was designed to obtain shorter pulse length. It consists of 4mm long Nd:YAG crystal and 0.7mm long V:YAG crystal. The initial transmission of the V:YAG part (85%) and the output coupler reflectivity (90%) was the same in both cases. The generated pulse length was independent on pumping power for both crystals. For longer (shorter) crystal it was equal to 6.2ns (1.7ns FWHM). The wavelength of linearly polarized TEM00 laser mode was fixed to 1338nm for longer crystal. In case of shorter crystal instabilities were observed for higher pump power. The average pulse energy was equal to 37μJ for longer crystal, and 15μJ for shorter one.

Comparative Performance of Passively Q-Switched Diode-Pumped Yb $^{3+}$-Doped Tungstate and Garnet Lasers Using Cr $^{4+}$:YAG Saturable Absorber

We investigated the continuous wave (CW) free-running and repetitive modulation in the kilohertz frequency domain of a passively Q-switched diode-pumped Yb:YAG, Yb:GGG, and Yb:KYW lasers by using Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> :YAG as a saturable absorber. The results presented in this paper are focused on the design of a passively Q-switched Yb-doped garnets or Yb-doped tungstates microlasers. The free-running performance of Yb:YAG, Yb:GGG, Yb:KGW, and Yb:KYW were characterized, and experimental parameters such as gain and loss were evaluated. We carried out a fit between our experimental results and an existing numerical model, which relates the experimental and the physical parameters of the ytterbium diode-pumped system to the minimal threshold pumping power. The best performance among the laser crystals was obtained for Yb:YAG laser. A maximum peak power of ap4.5 kW at an average output power of 1.32 W was extracted with an extraction efficiency of ap25%.

Diode End-Pumped Passively Q-Switched Nd3+:GdVO4Self-Raman Laser at 1176 nm

A compact diode-end-pumped passively Q-switchedNd3+:GdVO4/Cr4+:YAG self-Raman laser at 1176 nm isdemonstrated. When the T0 = 80% Cr4+:YAG saturableabsorber is inserted into the cavity, the maximum Raman laser outputreaches 175 mW with 3.8 W incident pump power. The optical conversionfrom incident to the Raman laser is 4.6% and the slope efficiency is6.5%. The pulse energy, duration, and repetition frequency of thefirst stokes laser are 4.5 μJ, 1.8 ns, and 38.5 kHz, respectively.There is strong blue emission (about 350–400 nm) can be observed inthe Nd3+:GdVO4 crystal when the process of stimulatedRaman scattering occurs, which is induced by the upconversion of theNd3+ ions.

Continuous-wave and Q-switched laser operation of Yb:NaY(WO_4)_2 crystal

Diode-pumped continuous-wave (cw) and Q-switched laser operations were demonstrated, for the first time to our knowledge, with a disordered Yb:NaY(WO(4))(2) crystal. A cw output power of 5.2 W at 1045 nm was generated with an optical-to-optical efficiency of 37%. The slope efficiency in the absence of thermal losses was 50%. With a Cr(4+):YAG saturable absorber to passively Q-switch the laser, an average output power of 2.0 W was obtained with a slope efficiency of 35%. The output pulse energy, duration, and peak power were 145 muJ, 26 ns, and 5.6 kW, respectively.

Doubly passively Q-switched intracavity-frequency-doubling &lt;inline-formula&gt;&lt;math altimg="none" display="inline" overflow="scroll"&gt;&lt;mrow&gt;&lt;msup&gt;&lt;mi&gt;Nd&lt;/mi&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;mo&gt;:&lt;/mo&gt;&lt;mi&gt;YAG&lt;/mi&gt;&lt;mo&gt;∕&lt;/mo&gt;&lt;mi&gt;KTP&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/inline-formula&gt; green laser with &lt;inline-formula&gt;&lt;math altimg="none" display="inline" overflow="scroll"&gt;&lt;mrow&gt;&lt;mi&gt;GaAs&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;math altimg="none" display="inline" overflow="scroll"&gt;&lt;mrow&gt;&lt;msup&gt;&lt;mi&gt;Cr&lt;/mi&gt;&lt;mrow&gt;&lt;mn&gt;4&lt;/mn&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;mo&gt;:&lt;/mo&gt;&lt;mi&gt;YAG&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/inline-formula&gt; saturable absorbers

By using both GaAs and Cr 4+ :YAG saturable absorbers simultaneously in the same cavity, a xenon-flash-lamp-pumped doubly passively Q-switched intracavity-frequency-doubling Nd 3+ :YAG/KTP green laser is realized. This laser can generate a more symmetric shape and shorter pulse width compared to the solely passively Q-switched intracavity-frequency-doubling green laser withCr 4+ :YAG or GaAs saturable absorber. A symmetric factor is defined to describe the temporal symmetry of the pulses quantitatively. The coupled rate equations under the plane-wave approximation are used to simulate the Q-switched process of the laser, and the numerical solutions agree well with the experimental results.

Analysis of a laser-diode end-pumped intracavity frequency-doubled passivelyQ-switched and mode-locked Nd:GdVO4/KTP laser

A diode-pumped intracavity frequency-doubled passively Q-switched and mode-locked c-cut Nd3+:GdVO4/KTP green laser with a Cr4+:YAG saturable absorber is experimentally demonstrated for the first time. Over 95% modulation depth for the mode-locked green pulses has been achieved. By using hyperbolic secant function methods, considering the influences of a continuous pump rate, the upper state lifetime of the active medium, and the excited-state lifetime of the saturable absorber, a rate equation model developed for Q-switched and mode-locked lasers has been given. With this model, the theoretical evaluations are in good agreement with the experimental results, and the width of the mode-locked green pulse was estimated to be about 280 ps.

Sub-nanosecond passively Q-switched Yb:YAG/Cr4+:YAG sandwiched microchip laser

We report on laser-diode pumped low-threshold, and compact passively Q-switched Yb:YAG microchip lasers, with Cr4+:YAG crystals as the saturable absorbers. The laser threshold at the fundamental wavelength of 1.03 μm is as low as 0.25 W, and the slope efficiency is as high as 36.8%, and the optical-to-optical efficiency is as high as 27% for the 95% initial transmission of the Cr4+:YAG crystal. A pulse width of 1.35 ns and peak power of over 8.2 kW was obtained. Using a 5 mm thick KTP crystal as the second-harmonic generation medium, 514.7 nm green light of 155 mW power was generated. The pulse duration of 480 ps was generated at 1.03 μm by using 85% of the initial transmission of the Cr4+:YAG saturable absorber. Stable single-longitudinal-mode oscillation and wide-separated multi-longitudinal-mode oscillation due to the etalon effect of the Cr4+:YAG thin plate was achieved at different pump power levels.

Diode-Pumped Passively Q-Switched Mode-Locked c-Cut Nd:GdVO4 Laser with Cr4+:YAG Saturable Absorber

A diode-pumped passively Q-switched and mode-locked (QML) c-cut Nd:GdVO4 laser with Cr4+:YAG saturable absorber is realized in a V-type folded cavity. The mode-locked pulse inside the Q-switched pulse has a repetition rate of 143 MHz, and its average pulse width is estimated to be about 460 ps. About 90% modulation depth for the mode-locked pulses has been obtained. Basing on a hyperbolic secant function method, a developed rate equation model for Q-switched and mode-locked lasers was introduced, in which not only the Gaussian distribution of the intracavity photon density and the influences of the continuous pump rate were considered, but the stimulated radiation lifetime of the active medium as well as the excited-state lifetime of the saturable absorber were taken into account. The numerical solutions of the equations are in good agreement with the experimental results.

Optimization of peak power of doubly Q-switched lasers with both an acousto-optic modulator and a Cr^4+-doped saturable absorber

A doubly Q-switched laser can obtain a shorter pulse with a stable repetition rate and high pulse peak power, which has been experimentally proved. By taking into account the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the acousto-optic (AO) Q switch, we introduce the coupled rate equations for a doubly Q-switched laser with both an AO modulator and a Cr(4+)-doped saturable absorber. These coupled rate equations are solved numerically. The key parameters of an optimally coupled doubly Q-switched laser are determined based on maximizing the peak power, which include the optimal normalized coupling parameter, the optimal normalized saturable absorber parameters, and the normalized parameters of the AO Q switch. The optimal normalized peak power, the corresponding normalized energy, and the normalized pulse width are also given, and a group of general curves are generated for the first time to our knowledge. The curves can give us a good understanding of the dependence of the optimal key parameters on the parameters of the gain medium, the saturable absorber, the AO Q switch, the resonator, and the spatial distributions of the intracavity photon density. The optimal calculations for a diode-pumped Nd(3+):YVO(4) laser with both an AO modulator and a Cr(4+):YAG saturable absorber are presented to demonstrate the use of the curves and the related formulas.

Satellite Pulse Generation in Diode-Pumped Passively Q-Switched&lt;tex&gt;$hboxNd:GdVO_4$&lt;/tex&gt;Lasers

We have both experimentally and numerically investigated the satellite pulse generation in diode-pumped passively Q-switched Nd:GdVO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> lasers with Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> :YAG saturable absorber. We show experimentally that satellite pulse generation is a general effect of the lasers under strong pumping, and its formation is always associated with the appearance of strong Q-switched pulses. Satellite pulse generation of the lasers is further numerically simulated based on a coupled rate-equation model. Our numerical simulations show that the phenomenon is caused by the finite lifetime of the lower laser energy level of the lasers

Passively Q-switched laser operation of Nd:LaB3O6 cleavage microchip

Pumped by a Ti:sapphire laser, a passively Q-switched laser oscillation from an unprocessed Nd:LaB3O6 cleavage microchip with a Cr4+:YAG saturable absorber has been demonstrated. The influence of the transmission of the output coupler on the pulse width and repetition rate at various absorbed pump powers has been investigated. A pulse with 2.8μJ energy, 2.2ns duration, and 29kHz repetition rate at 1060nm was obtained at the absorbed pump power of 1.25W and output coupler transmission of 3.2%, which results in 1.25kW peak power. The polarization and spectral properties of laser radiation were measured.

Experimental study of Ti:sapphire laser end-pumped Nd:YAG ceramic laserQ-switched by Cr4+:YAG saturable absorber

By employing a continuous-wave (CW) Ti:sapphire tunable laser as a pumping source and a Cr4+:YAG single crystal as the saturable absorber (SA), a passively Q-switched Nd:YAG ceramic laser has been demonstrated at room temperature. With an absorbed pumping power of 541 mW at 808 nm, an average output power of 61 mW at 1064 nm has been obtained with 3.5 mu J pulse energy, 15 ns pulse width and 18.18 kHz repetition rate, and the corresponding slope-efficiency is 15%. The relationships between the pulse width, repetition rate, average output power, pulse energy, and peak power on the absorbed pumping power for different initial transmission of the Cr4+:YAG SA are discussed separately. The Nd:YAG ceramic is one of the most promising laser materials for compact, efficient, all-solid-state pulsed lasers.

Optimization of Doubly&lt;tex&gt;$Q$&lt;/tex&gt;-switched Lasers With Both an Acoustic-Optic Modulator and a Cr&lt;tex&gt;$^4+$&lt;/tex&gt;-Doped Saturable Absorber

By considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the acoustic-optic (AO) Q-switch, we provide the coupled rate equations for a doubly Q-switched laser with both an AO modulator and a Cr /sup 4+/ -doped saturable absorber (SA). These coupled rate equations are solved numerically. The key parameters of an optimally coupled doubly Q-switched laser are determined,and a group of general curves are generated for the first time. These key parameters include the optimal normalized coupling parameter, the optimal normalized SA parameters and the normalized parameters of the AO Q-switch, which can maximize the output energy. Meanwhile, the corresponding normalized energy, the normalized peak power and the normalized pulsewidth are given. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the SA, the AO Q-switch,the resonator and the spatial distributions of the intracavity photon density. Sample calculations for a diode-pumped Nd/sup 3/+:YVO/sub 4/ laser with both an AO modulator and a Cr/sup 4+/ :YAG SA are presented to demonstrate the use of the curves and the related formulas.

Diode-pumped, passively Q-switched Nd:GdVO_4 green laser with periodically poled KTP and Cr^4+:YAG saturable absorber

With a laser diode as the pump source, a passive Q switching of an intracavity frequency-doubling Nd:GdVO4 green laser with periodically poled KTP has been realized with a Cr4+:YAG saturable absorber. The dependences of the average output power, pulse width, pulse repetition rate, pulse energy, and peak power on incident pump power at different small-signal transmissions of Cr4+:YAG are measured. The rate equations considering the Gaussian spatial distribution of the intracavity photon density and the effects of the amplified spontaneous emission (ASE) are presented to simulate the Q-switching process of this laser, and the numerical solutions are in agreement with the experimental results. We have further discussed the influences of the ASE parameter ξ on the laser performance.

Laser performance of Nd:LaB3O6 cleavage microchips passively Q-switched with a Cr4+:YAG saturable absorber

Passively Q-switched laser oscillation at 1060 nm from an unprocessed Nd:LaB3O6 cleavage microchip with a Cr4+:YAG saturable absorber has been demonstrated. The influence of absorbed pump power, output coupler transmission and cavity length on the output pulse characteristics has been investigated. For a plano-concave cavity with a cavity length of 28 mm, pulse with 100 mW average output power, 4.0 μJ energy, 17 ns duration, 25 kHz repetition rate, and 0.24 kW, peak power was obtained at the absorbed pump power of 1.42 W and output coupler transmission of 3.5%. For a plano-plano cavity with a cavity length of 5 mm, pulse with 85 mW average output power, 2.1 μJ energy, 2.3 ns duration, 40 kHz repetition rate, and 0.89 kW, peak power was obtained at the absorbed pump power of 1.42 W and output coupler transmission of 5.6%. Because a chopper with a 5% duty cycle was employed in the experiments to reduce the influence of pump-induced thermal loading, the above average output powers were obtained at the 5% duty cycle and extrapolated to 100%.

Investigation of passively synchronized dual-wavelength Q-switched lasers based on V:YAG saturable absorber

In this paper the results of a theoretical and experimental investigation of synchronized passive Q-switching of two Nd:YVO4-based solid-state lasers operating at two different wavelengths, is described. A V:YAG saturable absorbing material was used as a passive Q-switch performing the synchronization of the two laser fields. This material provides Q-switching operation at both 1064 and 1342 nm wavelengths simultaneously, saturating the same energy level. By adjusting the pump power of both lasers, it was possible to optimize the overlap of the two pulse trains and to switch between different states of synchronization. A theoretical model based on rate equations, which has been developed in order to investigate optical performance of the laser system, is in a good agreement with the experimental results. The principle of synchronized Q-switching can lead to new, pulsed all-solid-state light sources at new wavelengths based on sum-frequency mixing processes.

Diode-pumped passively Q-switched Nd:YVO_4 green laser with a periodically poled KTP and Cr^4+:YAG saturable absorber

A diode-pumped passively Q-switched Nd:YVO4 green laser with a periodically poled KTP and Cr4+:YAG saturable absorber is realized. The dependences of pulse repetition rate, pulse energy, pulse width, and peak power on incident pump power are measured for the generated green-light pulses. A rate-equation model is introduced to theoretically analyze the results obtained in the experiment, in which the spatial distribution of the intracavity photon density is taken into account. The numerical solutions of the rate equations agree with the experimental results.