On maximum compression of pulses in a homogeneous medium with dispersion

Stephen E. Harris

The Letter describes a technique for the spontaneous generation of chirped time-energy entangled photons. Transmitting either photon through an appropriate dispersive medium results in a temporally compressed, transform limited biphoton. At maximum bandwidth, the biphoton is a single cycle in length, with a waveform that has the same characteristic shape as a classical single-cycle pulse.

Sergei M. Arakelyan, Levon Gevorkyan, Yu. S. Chilingaryan

Alvin Katz, R. R. Alfano

Fam Le Kien, K. Hakuta, Alexei V. Sokolov

We present a general analysis for the interaction of a probe-laser radiation with a coherently prepared molecular Raman medium. We describe a general formalism that includes dispersive effects, such as group velocity and group-velocity dispersion (GVD). When dispersion is negligible, the analysis is especially simple and insightful. We show that molecular oscillations result in a modulated instantaneous susceptibility of the medium. The effect of the time-varying susceptibility on a probe-laser pulse is twofold: the output frequency becomes modulated because of the time-varying phase velocity, and the pulse shape becomes deformed because of the time-varying group velocity. We identify two mechanisms for pulse compression: (1) Frequency chirping with subsequent pulse compression by normal linear GVD (possibly in the same medium) and (2) Compression due to the time-varying group velocity. We analyze various aspects of pulse compression in the coherent Raman medium and derive conservation relations for this process. When we consider a probe-laser pulse that is much shorter than the molecular oscillation period, we observe frequency chirping, compression, or stretching of this pulse, depending on its relative timing with respect to the molecular oscillations. Based on our analysis, we propose a method for selective compression or frequency conversion of single ultrashort pulses.

T. A. Weber, Dennis Benedict Trizna

Recently a measurement of the velocity of longitudinal ultrasonic waves propagating through a phonon maser amplifier showed that the pulse traveled with the maximum or cutoff velocity at resonance. With an approximate dispersion rule for a homogeneously broadened spin-resonance transition, the propagation of the wave is analyzed using a method for the asymptotic expansion of Fourier-type integrals. This analysis, contrary to earlier studies, indicates that the pulse observed, or at least the leading edge of that pulse, was an amplified precursor (transient response). For a sinusoidal imput signal, the asymptotic wave form at a given position is given for all possible values of the time.

Nikolai S. Bukhman