Picosecond CO2 Laser Research Articles

High-speed low-voltage ultraviolet light source

A novel quasi-spark gap has been designed and constructed with high-speed and low-spark voltage characteristics. Ultraviolet light generating sparks can be operated at a rate of up to 25 kHz with pulses as low as 28 V. The photon pulse has a rise time of <10 nsec. Negligible breakdown delay and subnanosecond jitter have also been observed. It is an efficient UV point source capable of fast triggering and synchronization. A UV photon generation efficiency of 10−3 was estimated. The spectral properties of this gap were also analyzed. This gap has been incorporated into a picosecond CO2 laser system to trigger a plasma shutter in the generation of picosecond laser pulses.

Pulse-Duration-Dependent-Free-Carrier-Absorption in Semiconductors

ABSTRACTThe free carrier absorption in InSb was found to depend on the pulse duration of the picosecond CO2 laser pulse. This is interpreted as the effect of incomplete carrier relaxation within the laser pulse duration. An electron energy relaxation time of 5.6 ps was derived from the observation. The present experiment presents a new method of measuring relaxation times in semiconductors and metals.

High-speed, low-cost laser-triggered plasma shutter

Design and construction of a CO2 laser-triggered plasma shutter is described. An inexpensive pyroelectric detector and a novel needle-resistor spark gap, requiring an applied voltage of less than 500 V, are employed. The total electronic delay can be made to be less than 15 ns with subnanosecond jitter. This plasma shutter finds applications in producing picosecond CO2 laser pulses and in optical isolation.

CO2 laser-induced melting of indium antimonide

Using picosecond CO2 laser pulses, the following sequence of events was identified in high power laser-semiconductor interaction: (i) generation of a dense (≳1018 cm3) plasma, (ii) melting of the crystal by free-carrier absorption, (iii) formation of surface ripples at the breakdown threshold, and (iv) formation of a crater at higher intensities. The melting without breakdown region can be quite broad and may have potential applications in semiconductor processing and annealing.

Saturation of absorption in p-Ge using picosecond CO2 laser pulses

A time-resolved measurement on the recovery of saturation in p-Ge was performed with picosecond CO2 laser pulses. It was directly confirmed that the relaxation of hole excitation in p-Ge was faster than 40 psec and that this type of measurement can provide additional temporal information on picosecond pulses.