Y. S. Bai

Real‐time optical waveform convolver/cross correlator

We show that an inhomogeneously broadened sample, excited by a series of three resonant optical pulses, emits an optical signal whose electric field envelope closely approximates the convolution or cross correlation of the field envelopes belonging to two of the three excitation pulses. The convolution (cross correlation) function is obtained when the first (second) pulse in the excitation sequence is short compared to the temporal structure of the other two excitation pulses.

Coherent transient optical pulse-shape storage/recall using frequency-swept excitation pulses

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.

Experimental studies of photon-echo pulse compression

Photon echoes generated by long (i.e., 400–800-nsec) frequency-chirped optical pulses are found to possess (after compensating for avoidable material relaxation) up to 25% of the energy of the first excitation pulse and to have a duration determined by the total chirp bandwidth of the excitation pulses. In our experiment, echoes 30 times shorter than the first excitation pulse were observed.

Photon echo optical pulse compression

It is predicted that linearly chirped optical excitation pulses give rise to photon echoes whose shortness is limited only by the total material bandwidth that contributes to the echo signal. The photon echo process acts as a frequency‐dependent optical delay line whose dispersion is determined by the chirp rate of the excitation pulses rather than by their bandwidth. Consequently, long and short pulses can be compressed with equal facility without complicated alignment procedure. Accumulated echoes have similar properties and can be used with trains of weak excitation pulses.

Spectrally ordered Zeeman coherences and optical pulse-shape storage

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.

Field-inhibited optical dephasing and shape locking of photon echoes

Using an acousto-optically gated cw dye laser and working on the 555.6-nm absorption line of atomic(174)Yb, we have studied the shape of two-excitation-pulse photon echoes as a function of the duration and intensity of the second excitation pulse. Surprisingly, a long and intense second excitation pulse is found to generate an echo having a shape highly correlated with that of the first excitation pulse. This occurs because the high field of pulse 2 effectively stops dephasing processes throughout its duration.

Convolution, Correlation, And Storage Of Optical Data In Inhomogeneously Broadened Absorbing Materials

We discuss the light signals that are coherently emitted by some optical absorbers sub-sequent to excitation by a series of three laser excitation pulses. In some cases, the light signal emitted by the material duplicates the temporal shape of one of the laser in-put pulses. In other cases, the emitted signal represents the convolution or cross-correlation of two of the laser input pulses. In principle, digitally encoded signals of multi-gigahertz bandwidth can be convolved in real time, or, in suitable materials, stored for long periods. Output signals on the order of a few percent as intense as the inputs are possible. We provide experimental demonstrations of these effects, and discuss their implementation in optical signal processing and data storage systems.

Grazing-incidence dye lasers with and without intracavity lenses: a comparative study.

Tunable pulse dye laser technology has undergone rapid development since its introduction.115 Lisboa et al. 11 have recently reported that insertion of a lens in the cavity of a grazing-incidence pulsed dye laser1215 results in output pulses of higher power and narrower spectral width. They did not, however, indicate the extent to which the lens should improve dye laser performance or present systematic measurements of actual observed improvement. We present here results of an analytical and experimental study of this problem. We restrict our attention to the dye laser configuration of Fig. l(a), in which the cavity end mirror serves as the output coupler. Output taken through the end mirror has the advantage of being relatively free of broadband spectral background at the expense of being relatively low in power13 when compared to laser output taken from the zeroth order of the grating. Generally speaking, the linewidth of a dye laser is given by an expression of the form

Interaction of transient temporally modulated laser radiation with simple atomic systems

We point out that the frequency‐selective nature of the light‐matter interaction can be utilized to effect the storage of a spectral image (Fourier transform) of a temporally structured light pulse in the absorption profile of an inhomogeneously broadened atomic ensemble, and that the stored information can be subsequently recalled in the form of a free‐induction‐decay signal. Applications of this process to optical data storage are discussed. We also consider the interaction of a phase‐controlled, amplitude‐grated, resonant laser field with the atoms in a collimated atomic beam. We describe experiments wherein suitably prepared atoms are placed in pure stationary‐states (dressed states) of the atom + laser‐field system, and note that atoms in pure dressed states should have interesting spectral and dynamical properties.

Resonance fluorescence during phase-controlled transient excitation

Abstract The response of a two-level atom to a resonant driving field can be dramatically altered by a sudden shift in the driving fields phase. We discuss the implications of this fact with respect to the atoms transient fluorescence spectrum and relaxation properties.