Passive mode locking of lasers with the optical Kerr effect modulator

A detailed analytical investigation is presented of a nonlinear device termed the optical Kerr effect modulator (OKEM) which is used to passivelyQswitch and mode lock high-power lasers. Experimentally, an OKEM employing two standard quarter-wave plates is used to passively mode lock the Nd:glass laser. The mode-locking threshold dependence upon the parameters of the OKEM transmission function is definitively established. Pulsewidths and spectral measurements are given for the train of ultrashort pulses from the glass laser mode locked with the OKEM using two different Kerr liquids. The analytical and experimental results together indicate that the OKEM technique is a versatile and viable alternative and in addition overcomes most of the shortcomings intrinsic to the saturable absorber technique. The non-resonant nature of the OKEM suggests that it should find immediate application as a passiveQ-switching and mode-locking element for a Variety of lasers, including dye lasers, UV lasers, the CO2laser, and, notably, the high-power iodine laser.     

Passive mode locking of an energy transfer continuous-wave dye laser

The first passive mode locking of a continuous-wave energy transfer dye laser is reported. Using an argon ion laser-pumped mixture of rhodamine 6G and sulphur rhodamine 101 as the active medium, pulses of less than 500 fs duration have been generated over the spectral range 652-694 nm using two different saturable absorbers in a simple linear cavity without dispersion optimization. Pulses as short as 120 fs have been measured using standard second-harmonic generation autocorrelation techniques.     

Passive mode locking of flashlamp-pumped dye lasers in the 508 - 583 nm range

Measurements of the pertinent characteristics of a new saturable absorber dye (DASBTI) are presented, together with results which demonstrate its usefulness in the passive mode locking of several flash-lamp-pumped dye lasers operating within the 508-583 nm wavelength region.     

Passive transverse mode locking in a confocal Nd3+glass laser

Transverse passive mode locking by the dye technique has been obtained for a Nd³⁺glass laser with a confocal cavity. The laser energy is concentrated in a wave packet which propagates back and forth within the cavity along closed optical paths.     

GaAs对脉冲Nd:YAG激光器的调Q和锁模

本文分析半导体材料GaAs对1064nm激光的可饱和吸收特性,在闪光灯抽运的平凹腔和平凸腔Nd:YAG激光器中,插入GaAs样品作为调Q器件,实现了激光器的被动调Q运转,分别获得脉冲宽度32.7ns(平凹腔)和30.9ns(平凸腔)的激光脉冲。实验上研究了平凹腔腔长和输出镜透过率对调Q激光输出性能的影响。当平凹腔腔长增加到125cm时,观察到GaAs对1064nm激光的被动锁模。对上述实验结果给予了合理的理论解释。     

Parametric mode locking

The conditions under which a synchronously pumped intracavity parameter generation causes mode locking in a homogeneously broadened laser are investigated experimentally and theoretically. An expression for the steady-state duration of parametric mode-locked pulses is derived and compared with experimental results. Contributions from both parametric AM and FM mode locking are included, and the conditions to optimize pulse narrowing, frequency upconversion, and active dispersion compensation are determined and discussed     

Transverse mode locking

The possibility of phase locking the transverse modes of a laser is considered. It is shown that if a transverse mode set having a Poisson intensity distribution can be phase locked, a scanning laser beam can be produced.     

Passive mode locking of TE CO2lasers employing a germanium saturable absorber

A straightforward theory is presented for the passive mode locking of TE CO2lasers starting from spontaneous emission. Experimental measurements using a p-type germanium saturable absorber are in excellent agreement with the theoretical predictions. It is, therefore, possible to predict the quantitative effect on the mode-locking behavior of varying such parameters as the laser gain, linear and nonlinear losses, and the laser beam area ratio at the amplifier and absorber. The analysis presented indicates that it should be possible to obtain 10-15 ps duration pulses from multiatmosphere (≳5 atm) CO2amplifiers once the correct choice of the mode-locking parameters has been made.     

Multiple mode locking of lasers

Details of experimental results on higher order phase-locking phenomena of a He-Ne laser with a fixed cavity length and a fixed position of the laser tube in the cavity are presented. Two methods have been used in the experiments in order to obtain high bit-rate optical pulses. In one method modified Michelson-type resonators and a three-mirror Fabry-Perot resonator are utilized to suppress the oscillation of the undesired modes. Optical pulses of repetition rates up to about 600 megabits/s have been obtained. The second method utilizes an internal phase perturbation in a conventional Fabry-Perot cavity at a frequency nearly equal to a multiple of the longitudinal mode spacing. The repetition rate of optical pulses generated does not always coincide with the modulation frequency, but depends on the fine tuning of the frequency. In contrast to the former method, mode quenching is not necessarily required to produce multiple-bit pulses.     

Phase locking in an infrared short-pulse free-electron laser

The feasibility of the phase-locking procedure for the external selection of a single mode with reasonable power has been tested by simulation of the optical pulse evolution in a short-pulse free-electron laser using a model based on the self-consistent solution of the equations of motion for the electrons and the wave equation driven by single-particle currents. The simulations show that a high degree of coherence between successive pulses can be induced by a low-finesse etalon. Saturated operation in a greatly reduced number of modes, but with the same total power, is attained with a slight delay in the growth of the power as compared to the case without phase locking     

Continuous self-mode locking of infrared gas lasers

Observation of continuous self-mode-locked pulses induced only by the nonlinearity of the laser medium is reported for the 10.6-μ CO2, 3.39-μ He-Ne, and 3.508-μ He-Xe laser transitions. Optical spectra of these pulses were taken with a scanning Fabry-Perot intefferometer. Attainment of self-locking was strongly dependent on the second-order spatial Fourier component of the excitation density in the optical cavity.     

Transient evolution of passive mode locking

We present the first deterministic theory of the transient evolution of passive mode locking which gives a closed form expression for the pulse on each transit through the system. The theory is shown to be applicable to both CW and pulsed mode-locked laser systems. Included are studies of the buildup from noise, the mode-locking threshold, the subsequent evolution of the mode-locked pulse, the steady State operating point of CW systems, and the stability of the steady state. Simple criteria are established which enable the design of passively mode-locked systems to generate pulses of prespecified width and amplitude.     

Active mode locking with hybrid lasers

We present the results of a numerical study of active mode locking with hybrid lasers which contain an inhomogeneously broadened laser medium and an homogeneously broadened laser medium. The spectral, pulse, and gain characteristics of actively mode-locked hybrid lasers and the influence of the unsaturated gain, the saturation power, and the homogeneous linewidth on the pulse coherence and bandwidth are studied. The simulations show that coherent and shorter pulses are generated as compared to that by either an inhomogeneously broadened medium or a homogeneously broadened medium alone. Varying the unsaturated gain or the saturation power of the gain medium are two equivalent ways to obtain the same maximal coherent pulse bandwidth for given gain media. When different gain media can be selected, a larger pulse bandwidth can be obtained with the use of a broadband homogeneously broadened medium     

Passive mode locking in a diode-pumped Nd:GdVO/sub 4/ laser with a semiconductor saturable absorber mirror

We demonstrate Q-switched and CW passive mode locking in a laser-diode-pumped Nd:GdVO/sub 4/ laser with a semiconductor saturable absorber mirror. The repetition rate of the Q-switched envelope increased from 23.1 to 260 kHz as the pump power increased from 1.75 to 13.0 W. At a pump power of 13.7 W, the Q-switched mode locking changed to CW mode locking. The maximum average output power of 4.9 W with a 140-MHz repetition rate was obtained at a pump power of 17.9 W and the single mode-locked pulse energy was 0.035 /spl mu/J. The CW mode-locked pulse duration was measured to be /spl sim/11.5 ps.     

Passive phase locking of an array of four fiber lasers by mutual injection locking

In this paper, we report the passive phase locking of a four fiber lasers array by mutual injection locking. The four fiber lasers are mutually injected by four 5/5/90 couplers. Through mutual injection locking, good coherence has been obtained in the far field. The four fiber lasers can operate at the same wavelength with a stable output power. This scheme is quite easy to implement and can be extended to combine more beams.     

Threshold for spontaneous mode locking in Q-switched lasers

An expression for the threshold output power density for spontaneous mode locking inQ-switched lasers is derived. The resulting expression is readily evaluated in terms of laser emission cross section and linewidth and cavity geometry. The expression is evaluated for several experiments which previously reported spontaneous mode locking.     

Parameter ranges for CW passive mode locking

CW passive mode locking of a homogeneously broadened laser is considered. In the coordinate plane, whose abscissa is proportional to the small-signal saturable absorber loading, and whose ordinate is proportional to the small-signal gain, the following regimes are laid out: 1) steady-state single-pulse mode-locking solutions; 2) stability against relaxation oscillations; 3) self-starting of mode locking. The assumption is made that CW mode locking can be obtained only for a choice of parameters for which all three regimes overlap. We require further that the overlap regime be reached by a monotonic increase of small-signal gain (pumping), without passing outside regime 2). Under these conditions one may state requirements on the system parameters for the obtainment of single-pulse mode locking by a saturable absorber. The analysis explains why it has been impossible to mode lock passively the CW Nd:YAG laser, but passive mode locking of the CW dye-laser system is possible.     

Optical data inversion by locking mode competition

Using the behaviour of a Fabry-Perot semiconductor laser under the injection of two optical beams, all-optical data inversion is demonstrated without changes in the data carrier wavelength, together with a simultaneous wavelength conversion without data inversion. The output optical power at the inverted binary one state (-12 dBm) is greater than that corresponding to the inversion threshold (-16 dBm), which enables such operations to be repeated several times in cascade. These operations have been performed at a bit rate of 2 Gbit/s at 1.55 /spl mu/m.