Temporal Stretching of Laser Pulses

Abstract

Many lasers operate predominantly or only as pulsed sources and the pulse duration is determined by the duration of effective pumping, intra-resonator energy extraction rates, etc. However, in certain applications of the pulsed lasers, it is necessary to extend the duration of the laser pulses without reducing its pulse energy. The duration of laser pulses is increased by using laser pulse stretchers, which stretch the pulses temporally. An ideal laser pulse stretcher increases the duration of the laser pulse without introducing losses so the peak power of the laser is reduced without reducing its average power. The temporal stretching of laser pulses is vital for many applications of pulsed lasers. The temporal stretching of oscillator pulses of high beam quality is required in oscillator–amplifier systems for achieving high output power. The temporal stretching of pump laser pulses leads to an increase in energy conversion efficiency and tuning range along with a decrease in linewidth of the tunable dye lasers. While launching the laser pulses of high energy into optical fibers, the temporal stretching of laser pulses is done to reduce the peak power, without reducing the pulse energy, to save the input faces of optical fibers from damage. Thus the temporal stretching of laser pulses also increases the upper limit of transmission of pulse energy in the optical fibers. The optical pulse stretchers are used for removing laserinduced plasma spark generation in spontaneous Raman-scattering spectroscopy by reducing the peak power. In the guide star experiments, the pulse stretching of laser pulses is required to avoid saturation effects. The temporal pulse stretching is required in material processing because a stretched pulse is more efficient for heating the material. The temporal stretching of laser pulses is needed in optical microlithography to avoid degradation of semiconductor materials as well as optics. In the medical application of lasers, the pulse stretching of laser pulses is done to reduce the high peak intensities, which generally damage the tissues. The temporal stretching of laser pulses is done in holographic interferometry for removing the boiling effect, which is detrimental to the quality of the photographs. The ultrashort pulses are temporally stretched in the chirped pulse amplification (CPA) to avoid the nonlinear effects that lead to catastrophic damage. There are many more important applications, where temporal stretching of laser pulses is done. According to the type of the laser and the requirements of the application, various types of laser pulse stretchers, both passive and active, are developed for temporal stretching of laser pulses.