Generation and Characterization of Femtosecond Petawatt Ti:sapphire Laser

Abstract

A Ti:sapphire laser with output of 0.89PW/29.0fs based on the scheme of chirped pulse amplification has been developed. The high gain amplification was achieved in large aperture amplifiers by effective suppression of parasitic lasing.In this paper we report an ultrashort pulse and highly intense Ti:sapphire chirped pulse amplification (CPA) [1] laser system with the output peak power of 0.85PW and the pulse duration of 29.0fs. It is a typical CPA laser based on Ti:sapphire amplifiers, and consists of a self-mode-locked 10fs Ti:sapphire oscillator, acousto-optic programmable dispersive filter (AOPDF) [2], stretcher, regenerative amplifier, three stages of multipass amplifiers and a four-grating compressor.The signal pulse from oscillator was stretched to ~2ns with the bandwidth of 90nm. Then, it was injected to a regenerative amplifier. The cavity was a convex-concave structure and a 10mm long normal incidence Ti:sapphire rod was contained. A quartz birefringence filter was used in it for high gain and broad bandwidth amplification [3]. As shown in Fig.1, the output bandwidth from the regenerative amplifier was improved to 65nm from 28nm by using the birefringence plate. With the pump energy of 50-60mJ, the amplified laser energy was 8~10mJ without the filter. When the filter was used, the output was reduced to 3~4mJ at the same pump level. To make the system compact, the pump fluence and spatial mode matching between the pump and laser beams was optimized for the high efficiency conversion in the following amplifiers. For the pre-amplifier pumped from both side with an intensity of ~2.7J/cm 2 at 10Hz repetition rate, the thermal lensing in Ti:sapphire was a major problem. To compensate for it, a beam divergence was introduced when the laser from the regenerative amplifier was expanded, which will be matched with the pump intensity profile of the pre-amplifier. After five passes amplification, the output laser energy achieved 800mJ with the pump energy of 2.1J at a repetition rate of 10Hz. This beam was then enlarged to 32mm by using a Galilean telescope, and only the center uniform part with diameter of 24mm was injected to the next power amplifier.The laser energy of this system was mainly boostered in the power amplifier and final amplifier, which operated in a single shot limited by the pump laser (4 shots per hour). The pump laser was a Nd:glass laser system with the maximum output energy of 150J at 527nm. In our present experiments the pump laser normally delivers ~100J. After split, one beam with ~20% of the pump laser energy was sized at 26mm diameter and imaged relay to the power amplifier. The residual energy was sized to 60mm and also imaged relay to the final booster amplifier.The power amplifier contained a Ti:sapphire disk with size of 42×50×23(mm 3 ). Since this disk is rectangular, the parasitic lasing due to the Fresnel reflection of side surface is more serious. When the side surface was bare without absorption layer, the gain of this amplifier was small with even the very accurate time synchron...