B. I. Greene

Generation of optical pulses shorter than 0.1 psec by colliding pulse mode locking

We report a novel passive mode‐locking technique in which two synchronized counterpropagating pulses interact in a thin, saturable absorber to produce a short pulse. Continuous stable trains of pulses shorter than 0.1 psec are obtained using a ring laser configuration.

Picosecond nonequilibrium carrier transport in GaAs

We report a new picosecond optical technique for observation of nonequilibrium carrier transport. An ’’overshoot’’ electron velocity of 4.4×107 cm/sec is observed at short times in GaAs under appropriate electric field conditions.

Picosecond dynamics of hot carrier relaxation in highly excited multi-quantum well structures

Abstract Dynamics of hot carrier relaxation, exciton screening and subband level renormalization in GaAsAlGaAs multiple quantum well structures are investigated by time resolved measurements of optical absorption and gain following subpicosecond optical excitation. The cooling rate of the electron hole plasma in these two dimensional structures is approximately the same as for bulk GaAs at comparable photoexcitation density.

All-optical nonlinearities in organics.

Recognition that organic solids possess some of the largest all-optical nonlinearities of all known materials has resulted in an interdisciplinary effort directed at both the basic understanding and exploitation of these effects. Parallel efforts on ionrganic semiconductors have already reached a mature stage whereby the origin of the effects, together with the prospects for device applications, are well known and appreciated. In this article, a unified picture of nonlinear optical phenomena in both classes of materials is presented. The specific implications for organic-based optical devices are discussed.

Interferometric characterization of 160 fs far‐infrared light pulses

We report the first interferometric characterization of freely propagating, subpicosecond, far‐infrared (FIR) light pulses. FIR light was generated via short pulse photoexcitation of a semi‐insulating InP wafer. The half width of the intensity interferogram was 230 fs. The FIR light contained frequency components from 3 to 150 cm−1.

The subpicosecond kerr effect in CS2

Abstract The existence of a prominent subpicosecond birefringent response in CS 2 is demonstrated. New data are presented in an attempt to reconcile previous

Far-infrared light generation at semiconductor surfaces and its spectroscopic applications

Femtosecond pulses of far-infrared (FIR) radiation can be generated in the depletion field near semiconductor surfaces under optical excitation via the inverse Franz-Keldysh effect or electric-field-induced optical rectification. This coherent mechanism differs from previously proposed incoherent mechanisms and is expected to dominate for nonresonant excitation as well as for resonant excitation with optical fields. Two femtosecond time-resolved spectroscopic applications using a visible excitation pulse and a FIR probe pulse are described. >

Intervalley scattering in GaAs and InP probed by pulsed far‐infrared transmission spectroscopy

The dynamics of photoexcited electrons in GaAs and InP were studied using the transmission of 200‐fs pulses of far‐infrared radiation in the spectral range 15–100 cm−1. Kinetic traces of the infrared transmission as a function of delay between optical excitation and infrared probe show a probe‐limited decrease in transmission followed by a more gradual (0.7–2 ps) drop to a steady value, consistent with the slow return of electrons from high‐mass satellite valleys. Infrared transmission spectra, analyzed in the context of a Drude model, reveal density‐dependent electron mobilities 3–4 times below equilibrium n‐doped values. Electron‐hole collisions likely account for the lower mobility.

Picosecond relaxation dynamics in polydiacetylene-pTS

Abstract Time-resolved absorption spectroscopy as well as transient grating measurements were performed on polydiacetylene-pTS. Singlet exciton lifetimes of 0.8 ± 0.2 ps at 300 K and 1.1 ± 0.2 ps at 5 K were measured. We propose that the observed non-radiative relaxation proceeds through a conformationally relaxed singlet state which lives for roughly 1.0 and 3.4 ps at 300 and 5 K, respectively. Data pertinent to the formation of triplet excitons are also presented and discussed.

Picosecond pump and probe spectroscopy utilizing freely propagating terahertz radiation.

We demonstrate the feasibility of scaling up a terahertz-pulse generation scheme for use with a 10-Hz amplified femtosecond laser system. Visible pulsed excitation combined with a far-infrared probe should prove to be a powerful picosecond time-resolved technique.