A Laser System for the Generation of Pulses with Duration in the Pico-second Range and a Narrow Bandwidth
UCI researchers have developed a laser system for the generation of pulses with duration in the picosecond range and a narrow bandwidth. The laser system produces pulses with a duration of about 25 ps. The radiation can be tuned between 410 nm and 2000nm. The bandwidth of the radiation is spectrally narrow, close to the theoretical limit (the Fourier limit). Technically this system is an optical parametric oscillator (OPO); amplification is obtained in a parametric process rather than by population inversion. The oscillator is pumped by a pulse train from a Nd:Yag laser. In each roundtrip the bandwidth of the radiation is reduced by a grating-mirror assembly. Finally after a number of roundtrips a close to ideal pulse is obtained. This single pulse is then amplified by an OPA (Optical Parametric Amplifier) obtaining a single tunable narrow bandwidth pulse with a duration of about 25 ps. This source can be used for a number of spectroscopic techniques where ps pulses are needed as well as the highest achievable spectroscopic resolution.
The fundamental difference between this system and commercially available OPG systems is threefold: (i) The OPG systems only make one pass over the grating, which does not lead to a high spectral purity of the radiation; (ii) Existing commercial OPG systems do not have a stable cavity. A concave optic in the OPO selects resonator modes that are parallel both at the place of the amplifying medium and at the grating assembly, again making it possible to get narrow bandwidth radiation and making it easier to obtain oscillation, and (iii) The oscillator is saturated, making the intensity of the generated radiation less sensitive to variations in the intensity or the pump laser.
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