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Physical Review Letters

Measurement of Two-Photon Relaxation Time by Stark Switching

M. M. T. Loy

Published Jul 25, 1977• 19 citations
Publisher

Abstract

This Letter report the application of the Stark-switching technique to study the two-photon coherent precession effect. Using this technique, I have made the first time-do-main measurement of the collision-induced dephasing time in a two-photon transition in N${\mathrm{H}}_{3}$, and the result is compared with pressure-broadening measurements in the frequency domain.

DOI
10.1103/physrevlett.39.187

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This Letter report the application of the Stark-switching technique to study the two-photon coherent precession effect. Using this technique, I have made the first time-do-main measurement of the collision-induced dephasing time in a two-photon transition in NH3{\mathrm{H}}_{3}H3​, and the result is compared with pressure-broadening measurements in the frequency domain.
This Letter reports the first experimental observation of population inversion of a two-photon transition in NH3{\mathrm{H}}_{3}H3​ using the adiabatic rapid-passage technique. The population inversion was demonstrated by the observation of stimulated two-photon gain and emission. By use of this technique, the two-photon population relaxation time T1{T}_{1}T1​ was measured.
This Letter reports, for the first time, an experimental measurement of the collision-less dephasing time of the ${\ensuremath{\nu}}_{3}=2$ level in SF6{\mathrm{F}}_{6}F6​ using Doppler-free two-photon degenerate four-wave mixing. The measurement is performed in the time domain by use of a short-pulse CO2{\mathrm{O}}_{2}O2​ laser to establish a molecular two-photon coherent state. The coherent state is then probed as a function of time to yield a dephasing time of 1.8 nsec which is related to intramolecular dephasing rates.
By means of a time-resolved microwave spectroscopy experiment using the Stark switching technique, the authors have pointed out an exchange of rotational coherence from a level pair (a-a') of an A molecule to a level pair (b-b') of a B molecule in a gas at low pressure. The experiment exploits the linear Stark effect of the (a-a') line, the frequency of which is successively switched on resonance with the applied CW field to bring a coherence on the (a-a') level pair or with the (b-b') line frequency which is Stark insensitive and always off resonance with the applied CW field. The coherence exchange efficiency is maximum when the two line frequencies (a-a') and (b-b') are switched in exact resonance during a time around the transverse relaxation time T2. The radiation trapping effects are calculated and explain fairly well the experimental results obtained in a long cell. The collisional effects are shown to give a contribution which differs from the previous one only by its phase and its cell-length dependence. An experiment in a short cell is exploited to give a tentative upper limit for the collisional coherence transfers.
A novel coherent transient effect is observed following a rapid shift in the relative phase of an exciting laser and sample polarization. An analytical expression is derived for the signal which is a sum of exponentially decaying terms with characteristic times involving both T1{T}_{1}T1​ and T2{T}_{2}T2​. Phase switching is a powerful approach to the study of optical relaxation and is applied here to measure dephasing in LaCl3{\mathrm{Cl}}_{3}Cl3​: Pr3+{\mathrm{Pr}}^{3+}Pr3+.
A coherent optical transient technique has been used for the first time to study the Stark effect in atoms. This technique involves the recording of transients in the intensity of single-mode laser radiation transmitted by an atomic vapour following the sudden application of an electric-field pulse. It allows both absolute and differential Stark shifts to be measured to a precision which is limited only by the power-broadened natural linewidth of the transition. The feasibility of this technique is demonstrated by measuring the scalar ( alpha0) and tensor ( alpha2) polarisabilities associated with the sodium 32P1/2and 32P3/2levels of sodium. The resolution is such that the effect of the hyperfine structure on the Stark shifts has to be included in the analysis. Our values for the polarisabilities are alpha0=0+or-3.3 kHz (kV cm-1)-2and alpha2=28.1+or-3.9 KHz (kV cm-1)-2. These results are compared with experimental and theoretical values obtained by other authors.