R. Kachru

Multiple-bit long-term data storage by backward-stimulated echo in Eu(3+):YAlO(3).

We have observed faithful storage and retrieval of multiple data pulses for up to 5 h in Eu(3+):YAlO(3) crystal by using the backward-stimulated echo. We find no loss of echo fidelity as the storage time is increased. Furthermore the lack of cross talk between the input data pulses suggests that faithful long-term storage and retrieval of a large number of data pulses are possible. Our measured echo-storage lifetime of 3.8 h is to our knowledge the longest reported thus far.

Frequency-modulation spectroscopy with a pulsed dye laser

We report the use of frequency-modulation spectroscopy with a Nd:YAG-pumped dye laser of 5-nsec pulse duration. In spite of the fact that the dye laser is not transform limited and has 30% peak-to-peak intensity fluctuations, we are easily able to measure absorptions as small as 2%.

Optical header recognition by spectroholographic filtering.

We report on a novel scheme based on spectral holography for high-speed processing of optical header information. In this scheme, we rapidly analyze each incoming header by performing simultaneous correlation operations with a large number of headers stored in advance through angular multiplexing. Decoding is accomplished by identification of the directions that yield the maximum correlation signal. In a proof-of-concept experiment, two 5-byte ASCII addresses were decoded successfully without any ambiguity. The potential of this technique for high-speed packet switching is discussed.

High-efficiency nonvolatile holographic storage with two-step recording in praseodymium-doped lithium niobate by use of continuous-wave lasers

We have observed efficient two-photon, two-step recording in a praseodymium-doped lithium niobate crystal by use of cw lasers. Single-photon erasure during the readout at near-infrared wavelengths was found to be negligible. Nonvolatile holographic image storage was demonstrated. This progress is an important step in the realization of an economically feasible nonvolatile read-write holographic recording system based on low-cost semiconductor diode lasers.

Storage and phase conjugation of multiple images using backward-stimulated echoes in Pr3+:LaF3.

We have observed long-term storage and phase conjugation of multiple images by using a backward-stimulated echo scheme in the 3H4 -3Po transition of Pr3+:LaF3 crystal. The temporal order of the multiple-echo images is the reverse of that of the input images. Each of the echo images is a phase-conjugate replica of the input images and lasts as long as IS sec. This constitutes, in principle, the movie using a stimulated photon echo.

Time-domain holographic image storage

We describe a practical approach to image storage in a coherent time-domain optical memory that can be readily implemented with existing technologies. In this approach, two-dimensional images are stored spectroholographically in narrow ( less, similar 1-MHz) frequency channels of a time-domain storage material by use of a low-power laser, with one image per channel. Advantages of this approach include fast single-frame recording time, variable playback speeds, and random frame access. Experimental results demonstrating the use of this approach for high-speed, long-term image storage in Eu(3+):Y(2)SiO(5) are presented.

Frequency-modulation spectroscopy with a pulsed dye laser: experimental investigations of sensitivity and useful features

Systematic investigations of signal-to-noise ratios obtained in frequency-modulation (FM) spectroscopic measurements utilizing pulsed tunable dye lasers are reported which show that the noise becomes smaller as the modulation frequency is raised relative to the laser linewidth. Thus by raising our modulation frequency and narrowing our laser linewidth, we are able to detect ~0.1% absorption in spite of ~50% shot-to-shot fluctuations in the dye laser intensity. In addition several useful aspects of FM spectroscopy using pulsed dye lasers are demonstrated. The broad tuning range, ~5 cm−1, over which continuous scans may be made is demonstrated by recording absorption spectra of I2, Br2, NO2, and Na. The sensitivity of the technique to broad absorption features is shown by absorption spectra of the above species at atmospheric pressure. The Na was in a flame showing the potential usefulness of the technique in combustion diagnostics applications. Finally the nanosecond time resolution is demonstrated by observing the absorption of a transient population in the Na 3p state which has a lifetime of 16 nsec.

Coherent time-domain data storage with a spread spectrum generated by random biphase shifting

We report time-domain data storage of as much as 1.6 kbits at a rate of 40 Mbits/s in Eu3+:YOS. Use of a pseudorandom biphase shifting technique to spread the data spectrum proved to be of critical importance in preventing saturation of the transition by the long data pulse train. The experimentally inferred storage capacity, ≳ 5 × 104 bits/spatial spot, plus the competitive single-channel throughput rate, demonstrate the potential of this optical memory.

Frequency chirped copropagating multiple bit stimulated echo storage and retrieval in pr3+-yal03

Using a frequency-chirped ring dye laser, we have stored and recalled as much as 48 bits of information with the copropagating stimulated-echo geometry on the (3)H(4)-(1)D(2) transition in Pr(3+):YAlO(3). Since the copropagating excitation scheme has all the excitation pulses spatially overlapping, this technique will be useful to the practical implementation of stimulated-echo memory because there is no need for alignment of beams. Our experiments also demonstrate that frequency chirping of the excitation pulses dramatically improves not only pulse-shape reproduction by the echo pulse but also the shot-to-shot stability of the amplitude of the recalled data.

Reprogrammable optical matched filter for biphase-coded pulse compression

We demonstrate the use of stimulated echoes for high-speed phase-modulated signal processing. The specific example chosen here involves the compression of biphase-coded pulses-a technique widely used in radar systems to achieve high range resolution and high signal-to-noise ratios. Experimental results obtained with the 5- and 13-bit Barker codes are presented, along with the measurements of a systems dynamic range and signal-to-noise enhancement. Advantages of this technique over the existing methods for signal processing are discussed.