T. W. Mossberg

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.

Storage and time reversal of light pulses using photon echoes

We have studied the temporal profile of photon-echo signals generated by combined gated cw and pulsed dye-laser excitation of the inhomogeneously broadened, 555.6-nm absorption line of (174)Yb vapor. We find that the echo profile is, after time reversal, essentially identical with that of the first excitation pulse. We give a new analysis of this effect. Since time-reversed pulse reproduction should also occur in inhomogeneously broadened solid samples, and since we observe time-reversed reproduced pulses up to 4% as intense as the input pulse, this effect may have important applications in optical signal-processing systems.

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.

Storage and phase conjugation of light pulses using stimulated photon echoes.

We experimentally demonstrate that three-excitation-pulse (i.e., stimulated) photon echo signals can be backward-propagating, phase-conjugate replicas of the second echo-excitation pulse. Working on the 555.6-nm absorption line of atomic Yb vapor, echo signals, effectively 0.5% as intense as the second excitation pulse, are shown to reproduce image information carried by the second excitation pulse even when wave-front distorters are employed.

Studies of picosecond collisional dephasing in atomic sodium vapor using broad-bandwidth transient four-wave mixing

We have employed dye-laser pulses of 10-nsec duration and 1.5–10-nm bandwidth in a transient four-wave-mixing experiment to study high-perturber-pressure collisional dephasing in dilute atomic sodium vapor. Working at argon perturber pressures of several atmospheres, we are able clearly to resolve dephasing times over a thousand times shorter than our excitation pulse duration. Measured dephasing rates are in excellent agreement with those measured by more traditional methods. When both of the sodium D lines are excited, our signal displays quantum-beat-like oscillations at the 0.52-THz frequency difference between these two states. We provide a simple picture explaining the origin of these beats.

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.

Ultrahigh-frequency interference beats in transient, incoherent-light four-wave mixing

An angled-beam, transient four-wave mixing experiment is described in which nanosecond-duration, broad-bandwidth excitation pulses are employed to measure picosecond collisional dephasing and subpicosecond interference beats in atomic Rb vapor. The 7.2-THz interference beat, which corresponds to a 237 cm(-1) Rb fine-structure splitting, is apparently the fastest material-specific beat yet observed. We discuss practical limitations on the time resolution attainable with this technique and propose means of circumventing them by using broad-bandwidth collinear excitation beams and an angled narrow-bandwidth probe.

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.