Femtosecond temporal encoding in barium titanate

Up-converted photorefractive optical transient detection with femtosecond laser pulses

We report on experimental demonstration of optical transient detection (OTD) based on photorefractive two-wave mixing of femtosecond pulses. The demonstrated technique also combines nonlinear-crystal-based OTD with up-conversion from infrared into the visible range. The approach enables measurement of phase changes of a dynamic signal in the infrared using GaP- or Si-based detectors while suppressing stationary background. Experimental results reveal existence of the relation between input phases in the infrared and output phases in the visible wavelength range. We further present experimental evidence of additional merits of up-converted transient phase analysis under noisy conditions, such as residual continuous-wave emission affecting the ultrashort pulses from the laser.

Three-dimensional holographic imaging of living tissue using a highly sensitive photorefractive polymer device

Photorefractive materials are dynamic holographic storage media that are highly sensitive to coherent light fields and relatively insensitive to a uniform light background. This can be exploited to effectively separate ballistic light from multiply-scattered light when imaging through turbid media. We developed a highly sensitive photorefractive polymer composite and incorporated it into a holographic optical coherence imaging system. This approach combines the advantages of coherence-domain imaging with the benefits of holography to form a high-speed wide-field imaging technique. By using coherence-gated holography, image-bearing ballistic light can be captured in real-time without computed tomography. We analyzed the implications of Fourier-domain and image-domain holography on the field of view and image resolution for a transmission recording geometry, and demonstrate holographic depth-resolved imaging of tumor spheroids with 12 microm axial and 10 microm lateral resolution, achieving a data acquisition speed of 8 x 10(5) voxels/s.

Spatiotemporal control of ultrashort optical pulses by refractive-diffractive-dispersive structured optical elements

Structured optical elements that control the spatial and temporal characteristics of femtosecond light pulses are analyzed and synthesized. We show that unique spatiotemporal effects can be attained based on the diffraction, refraction, and dispersive effects that appear in the femtosecond regime. We argue that the design requirements for ultrafast optics are beyond the achromatization considerations that are usually applied to incoherent illumination because of the need to consider coherent effects. Despite fundamental limitations in the space-time control of ultrashort pulses, we show the potential of this technique to improve simultaneously the spatial and the temporal resolution of a lens and to generate ultrafast pulse sequences.

Time reversal of ultrafast waveforms by wave mixing of spectrally decomposed waves

Two different realizations of time-reversal experiments of ultrafast waveforms are carried out in real time by use of four-wave mixing arrangements of spectrally decomposed waves. The first, conventional, method is based on phase conjugation of the waveform's spectrum and achieves time reversal of real amplitude waveforms. The second arrangement of the spectrally decomposed waves spatially inverts the waveform's spectrum with respect to the optical axis of the processor and achieves true time reversal for complex-amplitude ultrafast waveforms. We compare and contrast these two real-time techniques.

Nonvolatile photorefractive spectral holography

We demonstrate nonvolatile storage of femtosecond pulses in a photorefractive LiNbO(3) crystal with recording and readout of spectral holograms at wavelengths of 460 and 920 nm, respectively. No degradation was observed after 24 h of continuous readout. We also show that we can realize the time-lens effect with our system by appropriately setting the ratio of the recording and the reconstruction wavelengths and the spectral resolution of the recording and the reconstruction processes.

Radio-frequency matched filtering by photorefractive optical holography

Matched filtering of megahertz-bandwidth signals by use of holograms recorded in a photorefractive crystal is demonstrated. Holographic recording of rapidly varying signals has heretofore been hampered by the relatively slow response of photorefractive crystals. For the first time, to our knowledge, synchronization between waveforms and short optical sampling pulses is used with acousto-optic electrical-to-optical conversion to build up static holograms of rf waveforms in a SBN crystal. Readout with a continuous input signal yields a time-resolved correlation with stored waveforms.

Photorefractive effect in a BaTiO(3) crystal at the 1.5-microm wavelength regime by two-photon absorption

We demonstrate the extension of the photorefractive effect in BaTiO(3) crystals to the 1.5-microm wavelength regime, which is obtained by two-photon absorption induced by intense femtosecond light pulses. The strong dependence of the effect on the light's intensity permits nondestructive readout of the photorefractively induced pattern by low-intensity light. One can thus use the photorefractive effect in the 1.5-microm regime to form optical components for communication applications.

Single-event observation of high-speed signals by interferometric spectral detection with a synthesized local oscillator

The single-shot detection of a high-speed 4-pJ optical signal is confirmed for the first time, to the author's knowledge, by use of a previously proposed interferometric spectral detection technique.

Pulsed-image generation and detection

We describe an experimental system that programs three-dimensional optical fields to 200-fs resolution over a 10-ps window by using photorefractive volume reflection holograms in lithium niobate. These pulsed images are detected with an imaging interferometric cross correlator.

Pulse shaping in volume reflection holograms

Ultrashort pulses are shaped by reflection from dynamic volume holograms recorded in azo-dye-doped epoxies. The spectral resolution and controllability of the reflection geometry are optimal for this application.

Real-time holographic storage of a temporal bit sequence by using angular multiple recording of spectral components

A novel method for storing a temporal bit sequence based on the angular multiple holographic recording of optical spectral components is proposed. In a preliminary experiment, a 4-bit-long nonreturn-to-zero 200-Mbit/s sequence is successfully recorded and regenerated from a photorefractive BaTiO(3) crystal.