Compression of low-intensity, phase-modulated light pulses

Huib J. Bakker, Paul C. M. Planken, L. Kuipers +1 more

If three light pulses interact in a second-order nonlinear-optical process with a phase mismatch, the pulses may acquire a significant phase modulation. This phase modulation leads to a modification of the spectrum of the pulses and may offer the possibility of compressing the pulses. In this paper we discuss the effects of the ratio of intensities of the interacting pulses and the amount of phase mismatch on the phase modulation using analytical and numerical results. When the phase mismatch is small, it turns out that the modulation is also strongly influenced by the initial phase difference between the fields. Finally, we study the combined effects of a phase mismatch and a difference in group velocity on the spectrum and intensity profile of the interacting pulses.

Viacheslav N. Chizhevsky, Sergei I. Turovets

Catherine M. Wykes

D. Grischkowsky, M. M. T. Loy

The recent observations by Loy of amplitude modulation and compression of infrared laser pulses caused by passage through the dispersive modulator (a cell containing dilute NH3 vapor with a Stark−modulated resonant frequency) are explained. It is shown that there is a formal equivalence between (i) the passage of a near−resonant light beam through a vapor with a time−dependent resonant frequency, and (ii) the passage of a frequency−modulated light beam through a vapor with a constant resonant frequency. For low−intensity light this equivalence reduces the problem to the optical analog of chirp radar.

Nicolai G. Basov, Vladilen S Letokhov

Hsiang-Yu Lo, Po-Ching Su, Yong‐Fan Chen

We report on the direct measurement of low-light-level cross-phase modulation (XPM) based on electromagnetically induced transparency (EIT) in the pulsed regime. A phase shift of 0.02 rad of a probe pulse modulated by a signal pulse with a peak intensity of 3 $\mathrm{\ensuremath{\mu}}\mathrm{W}/{\mathrm{cm}}^{2}$ was observed, which is the lowest intensity ever achieved for the N-type EIT-based XPM system. The experimental data make a quantitative prediction of the single-photon-level XPM phase shift arising from two interacting pulses with unequal group velocities that is consistent with the theoretical predictions proposed by Harris and Hau [Phys. Rev. Lett. 82, 4611 (1999)]. Furthermore, a proof-of-principle experiment demonstrating an enhancement of the nonlinear optical Kerr effect by shining the signal pulse twice is presented.