Continuous wave, Q-switched and mode-locked operation of alaser-pumped Nd:LNA laser

A linear cavity Nd:LNA laser pumped by a Ti:sapphire laser was investigated in a continuous wave (CW), Q-switched and mode-locked regime. A parallel study using a Nd:YAG crystal was also conducted using the same optics and intercavity elements. The slope efficiencies obtained with a 5% output coupler in CW operation are 41 and 55% for Nd:LNA (λ~1.054 nm) and Nd:YAG (λ~1.065 nm), respectively. Mode locking was achieved with a 360-MHz intracavity phase modulator and led to a relative improvement of the Nd:LNA versus the Nd:YAG device. In the Q-switched mode with an intracavity acoustooptic modulator, the performance of the two lasers is almost identical. With 300 mW of absorbed pump power at λ~800 nm, peak powers ~130 W were achieved in a 65-ns pulse with a 5% output coupler     

The output beam quality of a Q-switched Nd:glass slablaser

The authors have constructed and tested a flashlamp pumped, Q -switched, Nd:glass zigzag slab laser. The thermally induced optical distortion through the slab is minimized by uniform pumping and cooling and the use of corrective pump shields at the slab ends. The laser spatial output for Q-switched resonators has been measured and modeled. It is shown that a large aperture planar oscillator has an output divergence many times above the diffraction limit. Operation as a one-dimensional unstable resonator in the wide direction of the slab allows the efficient extraction of energy in a high-quality beam. Near-diffraction-limited laser output of 5 J at 4 Hz is achieved with a resonator that includes an intracavity telescope to correct for residual defocusing in the thin direction of the slab     

Short pulse injection seeding of Q-switched Nd:glass laseroscillators-theory and experiment

A 0.5-GW-peak-power solid-state laser source that is based on injection seeding a Q-switched Nd:Glass laser is discussed. In the first experimental demonstration, a Q-switched oscillator producing 101 mJ was seeded by a train of 11-ps pulses from a CW (continuous-wave) mode-locked laser to produce injection-mode-locked pulses under a 91-ns envelope. A theoretical analysis of injection seeding of a high-gain Q-switched oscillator by the output of a mode-locked oscillator is presented. The numerical analysis predicts the minimum signal power required for injection mode locking and the temporal shape of the output pulse. The experimental results agree well with the theoretical predictions. The amplification demonstrated by this technique is 104.4 dB, which is much greater than that demonstrated by a multipass or regenerative amplifier. The experimental advantages of injection mode locking include greater than 100 dB of effective amplification and noncritical cavity length adjustment of the seed resonator     

Integrated Q-switched multiple-cavity glass waveguidelaser

A novel Q-switching scheme, using rapid variation of the path difference between the cavities of a multiple-cavity resonator, is described. A thermooptic phase modulator was used to switch the cavity loss of a Y-junction glass waveguide laser between high and low states. Q-switched pulses with durations of 5 μs and peak powers of 70 mW were obtained     

Short-pulse, high-power Q-switched fiber laser

A high-power, laser-diode-pumped, Q-switched fiber laser operating at 1.053 μm which is suitable for use in time-multiplexed fiber sensor applications is described. The laser emits >1-kW pulses at 1.053 μm with 2-ns duration at up to 1-kHz repetition rates for an adsorbed pump power of only 22 mW at 810 nm. Tunable Q-switched operation over a 40-nm wavelength range has also been demonstrated     

Theory of the optimally coupled Q-switched laser

The general equations describing Q-switched laser operation are transcendental in nature and require numerical solutions, which greatly complicates the optimization of real devices. Here, it is shown that, using the mathematical technique of Lagrange multipliers, one can derive simple analytic expressions for all of the key parameters of the optimally coupled laser, i.e. one which uses an optimum reflector to obtain maximum laser efficiency for a given pump level. These parameters can all be expressed as functions of a single dimensionless variable z, defined as the ratio of the unsaturated small-signal gain to the dissipative (nonuseful) optical loss, multiplied by a few simple constants. Laser design tradeoff studies and performance projections can be accomplished quickly with the help of several graphs and a simple hand calculator. Sample calculations for a high-grain Nd:YAG and a low-gain alexandrite laser are presented as illustrations of the technique     

Self Q switching of a CW mode-locked Nd:YLF laser bycavity length detuning

The cavity length of a CW mode-locked Nd:YLF laser is detuned to investigate the effect of detuning on the output of the laser. Negative detunings of 0.4 to 2.4 μm result in periodic modulations of the pulse envelope. Further negative detunings of 2.4 to 3.4 μm produce undamped regular spikings, that is, stable self-Q-switching behavior with mode-locked pulses of 30~47 ps pulsewidths, which are as short as those of plain mode locking without Q switching. Similar self-Q-switching behavior is also produced by positive detunings, but the stability is very poor     

A Q-switched diode-pumped neodymium yttrium aluminumborate laser

A report is presented on the first Q-switched laser operation of a room temperature CW diode-pumped Nd:YAB laser. The intense peak fundamental power obtained by Q-switching significantly enhances the green light output from the Nd:YAB laser through the second harmonic conversion process. A peak green power exceeding 3 W was obtained with a CW diode laser input power of 180 mW, as compared to a green output power of only about 1 mW under pure CW operation. Nd:YAB shows considerable promise as a room temperature self-doubling material. Diode-laser-pumped Nd:YAB lasers show promise as compact, and reliable green sources for practical applications     

Optimization of Q-switched lasers

The authors extend the standard rate equation analysis to obtain expressions for the maximum peak power, maximum pulse energy, and minimum pulsewidth of a single Q-switched output pulse; the maximum power efficiency of a repetitively Q-switched laser; and the corresponding cavity output couplings. Results are obtained analytically and numerically, and a comparison of the two sets of results is made. As a first step in this process the authors derive general expressions for the peak power, pulsewidth, pulse energy, and power efficiency. The authors next differentiate these expressions in order to find the maxima or minima that optimize the parameter of interest. Differentiation is done with respect to the cavity output coupling     

Dynamics of Q-switched and mode-locked intracavity secondharmonic generation in a ring laser

The temporal dependence, spectral characteristics, and efficiency of a multimode Q-switched ring laser containing an intracavity second harmonic generator is described. Numerical studies show that such lasers are stable and efficient. Comparison with Q-switched lasers (not containing a second harmonic generator) demonstrates that the intracavity second harmonic generation lasers can be even more efficient than the fundamental laser due to nonlinear output coupling. General considerations for the operation of such lasers are described. Spectral characteristics of the output as a function of the gain of the active medium and the spectrum of the injected pulse are discussed. Instabilities at very high second harmonic conversion are observed     

Dye laser pumped Pr3+-doped fiber lasers: basicparameter investigation, CW operation, and Q-switched operation

An investigation of a Pr³⁺-doped Al₂O₃ -SiO₂ glass fiber is described. The basic material parameters like fluorescence lifetime and stimulated emission cross section, measured around 1048 nm, where the fiber has a strong emission band, are discussed. The pump source was a Rh6G dye laser at 590 nm. Continuous wave (CW,) operation with a slope efficiency of 26% and a pump threshold of 1.2 mW was obtained. The Q-switched operation, yielding a repetition rate up to 10 kHz with a maximum peak power of 30 W and a minimum pulsewidth of 25 ns, is described     

CW laser operation of Nd:YLF

CW laser operation of Nd:YLF is reported for the first time and, in a comparison to Nd:YAG, exhibits a lower threshold and higher single-mode average power. The TEM00mode volume of Nd: YLF was observed to be a factor of four larger than Nd:YAG, resulting in twice the TEM00mode average power. This result is attributed to the substantially lower thermal lensing of YLF with respect to YAG. In comparative measurements the stimulated emission cross section of Nd:YLF was found to be1.8 times 10^{-19}cm²for the π oscillation and1.2 times 10^{-19}cm²for the σ oscillation, as compared to2.4 times 10^{-19}cm²for Nd:YAG. The spectroscopic and lasing parameters of Nd:YLF indicate a potential for this material in high peak and average powerQ-switched applications.     

Effect of finite lower level lifetime on Q-switched lasers

Modeling of Q-switched laser operation for four-level lasers with finite lower-laser-level lifetime is presented. Extraction efficiency is reduced and pulse shape altered in comparison to the case of infinitely fast lower-level relaxation. This reduction in efficiency is dependent on the ratio of the lower state lifetime to the cavity lifetime, the number of times above threshold, and occupancy factors of the upper and lower laser manifolds. The model is applied to the case of a Nd:YAG laser operating at 1.064 μm. At worst, the extraction efficiency is 68% of that expected for infinitely fast relaxation     

A self-injection locked, Q-switched, line-narrowed Ti:Al2O3 laser

Line-narrowing, Q-switched, and self-injection locking are studied independently and as a system. Line narrowing is shown both theoretically and experimentally to depend on the inverse square root of the pulse evolution time interval. Q switching of the Ti:Al₂O₃ laser is demonstrated and the laser output energy as a function of the Q-switch delay is investigated. Self-injection is demonstrated and the operation of the laser is explored as a function of loss and the Q-switch delay. Self-injection locking is demonstrated and the performance as a function of the Q-switch delay is determined     

Optical parametric oscillation in MgO:LiNbO3 driven by adiode pumped single frequency Q-switched laser

Optical parametric oscillation tunable over the 940-1220-nm spectral region has been obtained from a monolithic magnesium-oxide-doped lithium niobate ring resonator. The monolithic optical parametric oscillator (OPO) was pumped by the 532-nm second harmonic of a diode-laser-pumped single-frequency Q-switched Nd:YAG laser. The exceptional frequency and amplitude stability of the single-frequency pump source provided stable OPO output pulses     

Electrooptically Q-switched 2.79 μm YSGG:Cr:Er laserwith an intracavity polarizer

Single Q-switched pulses have been generated in YSGG:Cr:Er with a 360-ns-risetime LiNbO₃ electrooptical modulator. It is shown that birefringence losses can be avoided and spiking emission eliminated by placing an additional polarizing LiNbO ₃ prism inside the laser resonator. Reproducible single Q -switched pulses of 200-ns duration have been generated     

Output beam focusability of a Nd:glass zig-zag slab laser

The focusability of a zig-zag optical path laser with a 230×65×5 mm Nd:glass for application to soft X-ray generation is described. A Q-switched laser output energy of 18.3 J with a pulse width of 28 ns was obtained in a phosphate glass LHG-5 (Nd:8 wt.%), with an extraction efficiency of 71% from a stored energy of 26 J at a pumping energy of 4 kJ. The focusability was achieved up to 6.2×10¹² W/cm² in a spot size of 100 μm, which was sufficient intensity to generate soft X-rays for X-ray lithography     

Picosecond injection laser: a new technique for ultrafastQ-switching

A modification of a method for self-Q-switching in a laser with an isotypic saturable absorber is suggested and implemented in a multisegmented injection laser. The method consists of the transportation of most parts of the excited absorber population to the amplifier. The carrier transport time must be less than the spontaneous recombination time in the absorber. In a three-section AlGaAs/GaAs double-heterostructure laser with modified Q-switching, optical pulses of 5 ps in duration with a repetition rate as high as 18.5 GHz and peak power above 10 W have been obtained. The latter value is the largest ever reported for a picosecond injection laser. Unique temporal and spectral features exhibited by these lasers have been observed, including the stepped variation of pulse repetition frequency, its dependence on the pump current, large emission spectral width (on the order of kT), spectral chaos and bistability     

Frequency stability of RF-excited CO2 waveguide lasersin gain-switched and Q-switched regimes

The behavior of an RF-excited waveguide laser is analyzed in a gain-switched and a Q-switched regime measuring the frequency sweep during the optical pulse. This enables laser-induced medium perturbations (LIMP) to be directly distinguished from the effects of the discharge power loading. The experimental observations confirm that the main perturbation in the laser output frequency is to be attributed to thermal energy variations. This gives the result of a Q-switch chirp more than one order of magnitude smaller than in the pulsed current mode, suggesting the use of Q-switching waveguide lasers in applications such as long range or Doppler laser radar systems. The chirp behavior in the pulsed current mode can show overshot relaxation corresponding to the propagation of density waves in the guide     

Spectroscopy and laser operation of Nd:ZBAN glass

The results of a study of the spectroscopic and laser properties of a Nd³⁺ doped fluoride glass are presented. Threshold energies and slope efficiencies are reported along with the stimulated emission cross section for the laser transition. The effect of excited state absorption of pump photons on the slope efficiency is investigated