J.-C. Keller

An amplitude correlator for broadband laser source characterization

Abstract We have developed a simple and versatile instrument for amplitude correlation measurements of broadband laser sources. The spatial fringe pattern produced by two beams issuing from a source is detected by a linear C.C.D. array. The fringe contrast is measured for each laser shot and is recorded versus the time delay between the beams. The apparatus has demonstrated picosecond time resolution together with nanosecond delay range capabilities.

Laser induced line narrowing in three-level systems: Application to the determination of the wavenumber of the 3s2-2p4 neon line (λ = 6328 Å)

Abstract The Doppler-free absorption line narrowing technique (A.L.N.) is applied to the 20 Ne (3s 2 -2p 4 -1s 5 ) three-level system, using a 127 I 2 stabilized He-Ne laser (λ = 6328 A) and a tunable single-frequency cw dye laser (λ = 5945 A). The relative frequency positions of the 20 Ne 3s 2 -2p 4 line and of some iodine hyperfine components are measured with an uncertainty of 1 MHz. The wavenumber of the 20 Ne line at low pressure (0.2 Torr) is deduced from these measurements and is found to be σ( 20 Ne, 3s 2 -2p 4 ) = 1579800.060 ± 0.005 m -1 . With regard to the previous results, the accuracy is increased by two orders of magnitude.

Dark Resonance and Optical Coherent Transients

Three broad-band laser pulses are used to drive transitions between three levels in Sr vapor. A four-wave mixing signal is monitored as a function of the delay time t12 between two of the pulses. For sufficiently strong fields, it is found that the signal, as a function of t12, can possess a dip which is narrower than the correlation time of the radiation fields. A theoretical interpretation of the results is presented in terms of the so-called dark resonance.

Stimulated Photon Echo for Elastic and Depolarizing Collison Studies

The stimulated photon echo technique has been applied previously to the study of small angle elastic scattering [1] but the method may also prove attractive to investigate quasi-resonant inelastic processes such as depolarizing, state-changing or energy pooling collisions. For these processes, total cross section have been obtained in the past using different experimental methods. However, they deserve to be reexamined in the perspective of their angular dependence. We present here the first angular analysis of a collisional depolarizing process, together with the determination of elastic scattering cross section in an excited state.

Broadband Light Photon Echoes and Collisional Energy Transfers

Broadband (incoherent) light pulses can be characterized in the time domain by the pulse duration τ L and by the inverse of the spectral width i.e. the coherence time τ c . For standard pump-probe experiments the time resolution is governed by τ L . In a nonlinear experiment involving the autocorrelation of the light field, the ultimate time resolution is determined by the coherence time τ c . Subpicosecond time resolution has been demonstrated in the measurements of transverse relaxation time T 2 using nanosecond light pulses [1].We report on the measurement of the evolution of a longitudinal structure with time resolution τ c ≪ τ L .