Light Gate Research Articles

Optical gating by bleaching-induced polarization anisotropy in organic dyes

A light gate based on optically induced polarization anisotropy in cryptocyanine-glycerin compares favorably with a CS2 light gate tested under similar conditions. The organic-dye device is more transmissive at giant-pulse excitation levels up to 10 MW/cm2, where both devices gated 1% of an incident probe beam, and is less sensitive to variations in the intensity of exciting light. A theory based on the anisotropic orientational distribution of excited dye molecules during bleaching is used to explain the data. Fair agreement is obtained if one accounts for the birefringence as well as the absorption anisotropy induced by the exciting pulse.

An optical up-conversion light gate with picosecond resolution

Up-conversion (or optical mixing) of light was used to measure the duration of subnanosecond optical pulses.

Time resolution and characteristics of a broadband picosecond continuum and light gate

A broadband continuum which last a few picoseconds can be generated in isotropic materials such as liquid H2O or D2O by single picosecond pulse excitation. It is demonstrated that the blue part of the spectrum is delayed relative to the red portion. A spectral analysis reveals a stimulated inverse Raman band around 260 cm−1 to the blue of the first anti-stokes emission. We offer two alternative explanations for this observation. The open time of the light gate is shown to depend on various parameters and in the case of a CS2 shutter, it may be extended over much longer time intervals than the pulse duration. At the same time we have observed depolarization and isotropic scattering of the interrogating light.

Influencing parameters in time resolved picosecond spectroscopy and a new light gate method

We show that the open period of a CS 2 light gate, triggered by a picosecond optical pulse, depends on the optical pathlength through the CS 2. An alternative to the light gate is suggested for time resolved spectroscopy. The working principle is based on scattering induced in CS 2. We have found that the broadband emission from H 2O or D 2O excited by a 5300 Å picosecond pulse is also of picosecond duration, but the blue part is delayed with respect to the red. From this delay time the lifetime of the ground state vibrational levels may be measured directly.

Ferroelectric ceramic light gates operated in a voltage-controlled mode

Plates of lead zirconate-lead titanate ferroelectric ceramic can have 1) low-loss optical transmission in thin, polished sections and 2) uniaxial birefringence dependent upon remanent polarization. These properties are potentially useful in electrically variable optical retarders, modulators, and latching light gates. This paper reports the results of measurements of basic light-gate devices using ferroelectric ceramic plates. A number of characteristics of the devices are reported; e.g., dependence of absolute light phase retardation on ceramic remanent polarization; dependence of ON-OFF ratio on exit aperture, switching pulse duration, and light wavelength; switching speed; and the dc hysteresis characteristic of the dependence of remanent polarization upon applied field. In the past, the use of ferroelectric devices under conditions producing partial switching has been discussed exclusively from the point of view of "charge-limited switching." This paper proposes a new mode of operating ferroelectric ceramic light gates using "voltage-controlled switching." Charge-limited switching results naturally when voltage pulses of short duration are used (appreciable ON-OFF ratios can be obtained from a light gate switched with pulses as short as 10 ns). As a result of the hysteresis in the dc switching characteristic, pulses with durations of the order of milliseconds or longer result in operation of the light gate in a voltage-controlled mode. Practical advantages resulting from this mode of operation are discussed.

A new bistable ferroelectric light gate or display element

The bistable light gate described utilizes ferroelectric domain switching in Bi 4 Ti 3 O 12 single crystals. Switching speeds in the order of 1 µs are readily obtainable.