Transient nutation and molecular echoes in microwave double resonance experiments

Arto V Nurmikko, S. E. Schwarz

B. Macke

François Rohart, P. Glorieux, B. Macke

By setting on resonance a polar gas at low pressure with an inhomogeneously saturating coherent wave, an oscillating transient nutation is observed, the fast damping of which may be principally related to the electromagnetic field inhomogeneity. The authors report the first experimental evidence of 'rotary' photon echoes allowing a partial restoration of the macroscopic polarisation. These 'rotary' echoes are the electric analogues of Solomon's 'rotary spin echoes' in NMR (1959) and must be carefully distinguished from the usual photon echoes related to the free induction decay (FID). The experiments have been performed in the microwave domain and show a dramatic reduction of the expected echo amplitude due to the molecular motion. Eventual applications, alternative methods of detection and the extension to the optical domain of these 'rotary' echoes are discussed.

Jose. Soto-Manriquez

Coherent transient effects are the optical analogs of the many transient phenomena seen in pulsed nuclear magnetic resonance experiments on spin systems. For example, photon-echo and optical nutation are the respective optical equivalents of spin echo and transient nutation of nuclear magnetic resonance. In Stark-switching and frequency-switching techniques the laser field and the molecules are brought into resonance in a sequence of pulses, the rest of the time they remain well off-resonance. So far it has been assumed that the off-resonance field does not have any measureable influence on the experimental results and is utilized to implement a very efficient detection scheme. This work discusses how the off-resonance field affects the coherent transient effects. It is shown here how this field, by inducing changes in the index of refraction as small as 10⁻⁶ produces easily observable effects in photon echo and delayed optical nutation.

P. R. Berman, J. Schmidt, Richard G. Brewer

J. I. Steinfeld, Paul L. Houston