We have experimentally investigated the creation of spectrally ordered nuclear and electronic Zeeman coherences in a gas-phase sample. A Zeeman coherence is generated through the sequential excitation of two coupled optical transitions. In our experiment, one transition was excited by a data pulse and the other by a short reference pulse. Subsequent excitation of one of these transitions by a short reading pulse transforms the Zeeman coherence into an optical coherence and leads to the emission of a time-forward or time-reversed duplicate of the data pulse. Output signals up to 5% as intense as the original data pulse were observed. We present a general analysis that is applicable to both gases and solids and find that the solid-state analog of this process will exist only if the inhomogeneous broadening of the two optical transitions is highly correlated.
We have experimentally investigated the creation of spectrally ordered nuclear and electronic Zeeman coherences in a gas-phase sample. A Zeeman coherence is generated through the sequential excitation of two coupled optical transitions. In our experiment, one transition was excited by a data pulse and the other by a short reference pulse. Subsequent excitation of one of these transitions by a short reading pulse transforms the Zeeman coherence into an optical coherence and leads to the emission of a time-forward or time-reversed duplicate of the data pulse. Output signals up to 5% as intense as the original data pulse were observed. We present a general analysis that is applicable to both gases and solids and find that the solid-state analog of this process will exist only if the inhomogeneous broadening of the two optical transitions is highly correlated.
Early in the study of nuclear magnetic resonance, it was recognized that coherent transient signals could possess shapes highly correlated with the radio frequency pulses used to generate them.1 Similar results were observed in the case of optical coherent transients.2 The information necessary to recreate the excitation pulse shapes has traditionally been seen to reside in the polarization of the sample or in the population difference between two energy states. Information so stored is constrained to relax at rates determined by the transverse T2 or the longitudinal T1, relaxation times of the excited nuclear or optical transition. Owing to the shortness of T1 and T2, coherent transient pulse shape storage has been viewed previously as having limited utility.
We demonstrate that frequency-chirped laser excitation pulses may be employed to generate coherent transient signals possessing the same temporal profile as a particular excitation pulse. In comparison with the short, fixedfrequency pulses used in previous studies of this effect, chirped pulses can be temporally longer, of lower intensity, and hence easier to generate. The experiment was performed on the 555.6-nm transition of vapor-phase atomic ytterbium, and pulse-shape information was stored in a coherence between excited-state Zeeman levels. A simple theoretical analysis of our results is presented.
In this series of papers we report on the generation and application of multiple pulse phase coherent sequences in optical spectroscopy.In this paper the effects of intense pulse trains on systems with only two resonant energy levels are analyzed, with particular attention to the effects of extreme inhomogeneous broadening and population depletion to nonresonant levels.It is shown that these effects, which are present in virtually all optical systems, make the simple gyroscopic model of optical coherent transients invalid.Exact calculations show, e.g., that a two-pulse photon echo is not maximized by a 1:2 length ratio for the pulses; that the maximum excited state population is not created by a 180" pulse; and that three equal pulses are almost as effective as a 1:2:1 ratio for producing three pulse echoes.The role of pulse phase is extensively analyzed.Pulse sequences are proposed and experimentally demonstrated which permit optical phase sensitive detection and measurement of ground state relaxation parameters.The experimental results are based on an extension of the acousto-optic modulation and fluoresence detection techniques of Zewail and Orlowski [Zewail et al., Chem.Phys.Lett.48, 256 (1977); Orlowski et al., ibid.54, 197 (1978)).The relative merits offluorescence and transverse polarization detection are discussed, and fluorescence detection is shown to be more generally useful for these new sequences.Finally, composite pulse trains are shown to be capable of substantially increasing the signal available from highly inhomogenously broadened transitions.In paper II we extend the treatment to multilevel systems with some emphasis on solid state applications.
In this series of papers we report on the generation and application of multiple pulse phase coherent sequences in optical spectroscopy. In this paper the effects of intense pulse trains on systems with only two resonant energy levels are analyzed, with particular attention to the effects of extreme inhomogeneous broadening and population depletion to nonresonant levels. It is shown that these effects, which are present in virtually all optical systems, make the simple gyroscopic model of optical coherent transients invalid. Exact calculations show, e.g., that a two-pulse photon echo is not maximized by a 1:2 length ratio for the pulses; that the maximum excited state population is not created by a 180° pulse; and that three equal pulses are almost as effective as a 1:2:1 ratio for producing three pulse echoes. The role of pulse phase is extensively analyzed. Pulse sequences are proposed and experimentally demonstrated which permit optical phase sensitive detection and measurement of ground state relaxation parameters. The experimental results are based on an extension of the acousto-optic modulation and fluoresence detection techniques of Zewail and Orlowski [Zewail et al., Chem. Phys. Lett. 48, 256 (1977); Orlowski et al., ibid. 54, 197 (1978)]. The relative merits of fluorescence and transverse polarization detection are discussed, and fluorescence detection is shown to be more generally useful for these new sequences. Finally, composite pulse trains are shown to be capable of substantially increasing the signal available from highly inhomogenously broadened transitions. In paper II we extend the treatment to multilevel systems with some emphasis on solid state applications.
Coherent population trapping (CPT) in a three-level atomic medium pumped by two subsequent short optical pulses is considered under the condition of negligible population decay from the excited optical state. It is shown that the amount of atomic population transferred to the excited state by the combined action of the pulses strongly depends on the phase of the ground-state coherence excited by the first pulse at the arrival time of the second pulse. Oscillatory behavior of optical excitation efficiency on the time delay between the pulses is predicted. It is also shown that saturating optical pulses can produce population inversion in a resonantly pumped quasi-two-level system. A class of solid materials in which the predicted phenomena can be observed at room temperature is found. It includes some rare-earth and transition-metal doped dielectric crystals where Orbach relaxation between ground-state Zeeman states is suppressed: ruby, alexandrite, and several others. On the basis of the theoretical predictions, experimental observation of Ramsey fringes in CPT spectrum of ruby is reported.
A theoretical analysis of the optical coherent transients that arise when a sample of two-level atoms is irradiated by a sequence of three broad-bandwidth pulses is presented. The first two pulses have a relative delay time of order of the correlation time of the pulse fluctuations and are sent into an atomic vapor from different directions. These pulses, whose temporal width is much greater than the delay time, can be correlated with one another and can be strong enough to saturate the two-level atomic transition. The third pulse is weak, noncorrelated with the first two, and is delayed in time so that it does not overlap them. We present a detailed examination of the transient signal that is produced when the third pulse is scattered by the spatial gratings in the population difference of atoms created by the first two pulses. Taking into account the effects of inhomogeneous and homogeneous broadening, we calculate the intensity of the transient signal, emitted in different directions, as a function of delay time. The signal is found to depend dramatically on the intensities of the excitation pulses. It is shown that, for strong excitation pulses, there is a direct dependence of the signal on the cross-correlation time of pulses ${\mathrm{\ensuremath{\tau}}}_{\mathit{c}}^{12}$ that does not exist when the pulses are weak. In particular, the strongest signals exhibit a peak of width of order ${\mathrm{\ensuremath{\tau}}}_{\mathit{c}}^{12}$. This peak can have a very narrow dip near its maximum whose width is much smaller than ${\mathrm{\ensuremath{\tau}}}_{\mathit{c}}^{12}$, if the pulses are fully correlated. We develop a representation of the time evolution of the Bloch vector of a two-level atom, driven by time-delayed pulses, that enables us to explain our results. In this representation, the two time-delayed pulses are replaced by two fully overlapping pulses having some effective amplitudes and atomic field detunings.