ИСТИНА

Precise synchronization of mode-locked pico- and femtosecond lasers integrated in technological and research complexes is a crucial issue for many applications. Jitter of output train of pulses respective to phase of periodic reference signal in continuous wave (cw) lasers can be effectively suppressed up to femtosecond level by means of feedback controlled cavity adjustment. Cross modulation approach gives even more synchronization accuracy. However, high-peak-power laser systems based on cw oscillators with option of precise optical synchronization are overly complex and expensive for most practical applications. High-peak-power mode-locked picosecond lasers with pulsed (qcw) pump are applicable for such fields as high precision laser micromachining, soft X-ray generation, laser photo injection for electron accelerators, optical parametric chirped-pulse amplification, routine time-resolved spectroscopic measurements, laser ranging etc. Systems based on pulsed oscillators may have definite advantages in comparison with cw ones, providing high pulse energy at the oscillator output, better efficiency of energy consumption, lower thermal loading, relative simplicity and compactness. At the same time, commonly used in cw lasers techniques of roundtrip frequency locking to external rf signal via control of cavity length are inapplicable at pulsed pump approach since generation process in each laser shot starts from spontaneous noise and typically has too short duration both for phase detector operation and for active cavity adjustment. Thereby precise synchronization problem at pulsed pump has some other meaning than in the case of using of cw pump. In general pulse position in cavity associated with internal active mode locking (AML) signal. Laser synchronization with external rf signal or even with some random event realized by setting phase of AML signal to appropriate value at the beginning of corresponding pump pulse. Ultrashort pulse makes limited number of roundtrips during generation process development in each pump pulse. Its time position is defined by several factors such as amplification in active element, passive mode-locking based on semiconductor absorber mirror, action of negative feed-back and active mode-locking by means of electrooptical amplitude modulator. Deviation of time interval between triggering event and pulse output (jitter) is mainly determined by width of “temporal transparency window” which is formed by cumulative action of the above factors in the oscillator. In the present paper, we discuss experimental and modeling results on jitter reduction in picosecond pulse-diode-pumped Nd:YAG and Nd:YLF lasers within output pulse duration level of several tens of picoseconds.