Abstract
The coherent response of excitons and low-energy continuum excitations has been determined in InP at 5 K using spectrally resolved four-wave mixing employing 40 fs pulses in a self-diffraction geometry. The excitons were studied under simultaneous excitation with free carriers of density 10,N,10 cm. Excellent agreement between experiment and a simple theory based on excitation induced dephasing is obtained for an exciton dephasing rate which varies as N with a'0.5 in the density range. The sublinear dependence is suggestive of carrier-exciton screening effects; however, a variation in exciton oscillator strength and/or phasespace filling effects may also be contributing to the density dependence of the four-wave-mixing signal. For the continuum excitations we spectrally resolve the influence of LO phonons on continuum dephasing. Below the threshold for LO-phonon emission by electrons we determine a dephasing rate of ;8 ps at N55 310 cm; for states just above the threshold for LO-phonon emission, the dephasing rate is .13 ps, our resolution limit. @S0163-1829~99!06024-5#
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