Ultrafast Infrared Lasers and Detectors.

An experimental study on ultrafast infrared laser system and a theoretical study on novel avalanche photodiodes (APD) are presented. The experimental work started with high throughput optical pulse compression technique at 1064 nm. Phenomena like self-phase modulation, stimulated Raman effects, and depolarization in various fibers were experimentally investigated. Two well characterized, synchronously pumped ultrafast infrared dye lasers were then built. The first dye laser is a picosecond Styryl-9 dye laser which is designed for the characterization of AlGaAs/GaAs material system. It can generate 2 ps tunable pulses from 790 nm to 880 nm. It can also provide 7 ps 30 nm broadband pulses. The second dye laser is a femtosecond IR 26HFB dye laser which matches with the bandgap of the InGaASP/InP material system. It provides 300 fs pulses tunable from 1240 nm to 1350 nm or 220 fs 70 nm broadband pulses. We synchronized these two lasers and drove them with one cw mode-locked Nd:YAG laser. Pump-and-probe experiment on a doped glass was performed by using broadband pulses of the Styryl-9 dye laser as probe. Time resolved transmission spectra were easily collected. They provided information of the carrier dynamics. In the theoretical work on structures and performances of the superlattice APD, a simulation program capable of predicting noise and gain was first developed. The avalanche gain was calculated according to the lucky-drift impact ionization theory. The excess noise calculation was based on discrete statistical process as well as a previously derived formula. The program successfully predicted device performances in bulk materials. It was then applied to the new device structures. Based on calculations, a new approach which could improve the ionization k-ratio with a sharp p-n junction was proposed. Novel detector structures with low excess noise, high speed, and low bias voltage were also presented.