Development of EM field in lasers with rotating mirrorQ-switch

A fast-Fourier-transform (FFT) computational scheme based on a Fourier expansion technique is developed to calculate the development of an electromagnetic (EM) field from spontaneous noise inside a loaded rotating mirror Q-switched laser. A rate equations analysis is also carried out, using the FFT-calculated dependence of the diffraction loss on the fixed Q-switch mirror tilt angle. The computational results are compared with the output characteristics of an eye-safe (λ=1.54 μm) erbium glass laser. The experiments are in good qualitative and quantitative agreement with the predictions of the FFT mode. The model reveals short-duration intense spatial regions, as well as two types of temporal modulations of the laser output pulses. These modulations are attributed to the inhomogeneous development of the laser field in the longitudinal and transverse laser resonator direction. These irregularities must be taken into account when calculating eye-safety levels of rotating mirror Q-switched lasers     

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     

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     

Mode-locked operation of a Nd:YLF laser and amplification in aQ-switched Nd:glass slab laser

A Nd:YLF laser pumped with a CW dye laser and acoustooptically mode locked at 38 MHz has an output power of 130 mW and a pulse length of 60 ps. Insertion of intracavity etalons and misaligning the mode locker allows for stable operation with a continuous range of pulse lengths from 60 ps to 4 ns. The 1.053-μm emission permits amplification of these pulses in a Q-switched Nd:phosphate glass slab laser oscillator up to intensities limited by optical damage     

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     

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     

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     

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     

Output energy characteristics of optimally pumped rotating mirrorQ-switch lasers

The author develops a simple analytical formula for the key laser resonator and Q-switch parameters of an optimally pumped rotating mirror Q-switch laser. The analytical expression developed relates the maximum attainable single pulse output energy to the laser parameters such as rotating mirror speed, output mirror reflectivity, length of the resonator, and the absorption cross section of the laser media on the basis of the experimentally measured mechanical Q-switch loss form. Good agreement between theory and the output performance of a test Nd-glass laser has been demonstrated     

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     

A single frequency Nd:YAG ring laser pumped by laser diodes

The design and operation of a diode-pumped Nd:YAG ring laser is described. The laser is shown to be a highly versatile device, capable of efficient generation of both the fundamental and second harmonic frequencies, CW and Q-switched. Single-frequency outputs in excess of 540 mW at 1.06 μm and 18.9 mW at 532 nm output were obtained, whereas multi-longitudinal mode Q-switched operation produced 22.4 μJ per pulse at 5 kHz in the fundamental and 7.3 μJ power pulse at 532 nm     

Short-pulsed 2.1 μm laser performance of Cr,Tm,Ho:YAG

An examination is conducted of Q-switching in flashlamp-pumped Cr,Tm,Ho:YAG 2.1 μm lasers. Experiments show that short-pulse operation in this material can exhibit comparable efficiencies to the long-pulse operation mode. Losses in overall efficiency are shown to be largely due to mode restriction in the resonator. A three-pulse extraction format is shown to improve slope efficiency by more than 200% compared to single Q-switched pulse extraction. The optimal interpulse interval was determined, revealing the time scale of the Tm sensitization process. Spectral shifts in the short-pulse operation mode were observed. Simultaneous dual-wavelength emission was found to be the most common mode of operation for the Q-switched laser     

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     

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     

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     

An EMQ-switched CO2 laser as a pump source for afar-infrared laser with a high peak power and a high repetitionrate

A modified current pulsed Q (EMQ)-switched CO₂ laser which is Q-switched by a mechanical beam chopper in combination with a pulsed discharge current is discussed. The laser produces a very stable output with a peak power greater than 1 kW at a repetition rate of 1000 p.p.s. for all transitions in the P and R branches of the CO₂ spectrum. A CH₃F laser pumped by the EMQ-switched laser produces 496 μm radiation in a 6.5 W peak, 100 ns pulses at 500 p.p.s. in the lowest loss EH₁₁ mode     

Optical parametric amplification of a 1.54-μm single-mode DFBlaser in a Ti:LiNbO3 waveguide

Optical parametric amplification of radiation from a 1.54-μm single-mode DFB laser in a Ti:LiNbO₃ waveguide has been investigated by measuring the idler created in the nonlinear process. The pump was a frequency-doubled Nd:YAG laser at 532-nm wavelength, operated either Q-switched or both Q-switched and mode-locked to avoid permanent surface damage and to minimize photorefractive index changes. On comparison with theoretical predictions, the output was found to correspond to a pump power one order of magnitude below the true power in the waveguide. The highest gain obtained was 4.7 dB with 49 W of pump power in a 27-mm-long waveguide. Although the experimental results can be improved, it is obvious that the major difficulty to overcome is the large pump power required. The prospect of decreasing the power requirement by using materials with higher effective nonlinear coefficients or by using quasi-phase-matching techniques is discussed. A more fundamental drawback is that the amplification is polarization dependent, and it is unclear how this can be handled     

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     

Laser diode-pumped internally folded Nd:YAG laser

A diode-pumped Nd:YAG laser in which the gain element is fabricated in the shape of an isosceles right-angle prism is described. An orthogonal face forms the highly reflective end of the resonator, while the hypotenuse serves as an internal fold mirror. Scaling was demonstrated by pumping the gain element along three axes simultaneously. The maximum power obtained was 1.3 W at 1.06 μm and 128 mW at 532 nm. Repetitive Q-switched operation is also reported     

A 5 kW CW CO2 laser using a novel negative-branchunstable resonator with a phase-unifying output coupler

A 5 kW CW CO₂ laser using a negative-branch unstable resonator (M=-1.5) is proposed and characterized experimentally. The resonator consists of a stepwise variable reflecting output coupler, called the phase-unifying output coupler, and a total reflector. A 5 kW CW laser beam with diffraction limited quality (2&thetas;=0.45 mrad) is obtained and affected by the focal point in the resonator. The misalignment angle to reduce the laser power to 95% is improved by a factor of 19 compared with a positive-branch unstable resonator (M=1.5) with a phase-unifying output coupler at the same resonator length