M. Gottlieb

Optical response of epitaxial films of YBa2Cu3O7−δ

We present the results of measurements of optical detection in epitaxial films of YBa2Cu3O7−δ, at wavelengths of 0.63 and 10.6 μm. In contrast to the behavior observed in granular materials, these films appear to show no evidence of nonequilibrium response (breaking of Cooper pairs by photons), but only a bolometric effect (heating of the sample by radiation) in the resistive transition regime. This suggests that epitaxial films do not contain intrinsic links weak enough to be modulated by the incident radiation. For 0.63 μm radiation, mechanically chopped at 725 Hz, measurements of a 10 μm ×90 μm bridge yield a bolometric responsivity of approximately 4×103 V/W, and a detectivity D* of more than 108 cm Hz1/2/W.

Spatial resolution of imaging noncollinear acousto-optic tunable filters

The spatial resolution limit of noncollinear acousto-optic tunable filters used for imaging with incoherent light is derived based on phase-matching requirements. It is shown that the noncollinear filter can achieve near diffraction limited imaging. This conclusion was verified experimentally.

Acousto‐optic properties of some chalcogenide crystals

We report results of extensive measurements on the acousto‐optic properties of several sulfosalt‐type chalcogenide crystals. These materials typically are transparent from the near ir to the intermediate ir, with refractive indices ranging from 2.5 to 3. Their acoustic velocities are among the lowest of any material, and ultrasonic attenuation remains low for frequencies to 500 MHz. These properties lead to exceptionally high acousto‐optic figures of merit.

Temperature sensing in optical fibers using cladding and jacket loss effects

A theoretical analysis is given of methods using transmission intensity effects in optical fibers as temperature sensors. The underlying mechanism involves temperature-dependent coupling of the evanescent field through a relatively thin cladding layer onto a lossy jacket. The temperature dependence comes about through the refractive indices of the core and cladding materials, which are chosen along with the fiber dimensions to give the desired response.

Tl3AsSe3 noncollinear acousto‐optic filter operation at 10 μm

An infrared tunable acousto‐optic filter based on Tl3AsSe3 in a noncollinear configuration is described. The filter was operated at CO2 laser wavelengths from 10.8 to 9.3 μm, with corresponding rf drive frequencies in the 15–18‐MHz range. Filter bandwidths are of the order of 20–30 cm−1, and the measured tuning rate is 18.0 kHz/cm−1 at 10 μm.

High-performance acousto-optic materials - Hg2Cl2 and PbBr2

New results achieved with recently grown Hg2Cl2 and PbBr2 crystals are described. With an optimized crystal growth technique Hg2Cl2 crystals were grown that show a significantly reduced acoustic attenuation compared to prior crystals, from 13.4 to 8 dB/μs-GHz2. These crystals allow the development of Hg2Cl2 Bragg cells with time-bandwidth product figures in the 5100 to 6900 range, frequency operation as high as that for Te02, and resolution about 25% higher than TeO2 for similar crystal lengths. PbBr2 crystals were also grown that exhibit a large figure of merit (M2 550) with an attenuation coefficient of 12 dB/μs-GHz2. This material may be the choice for infrared devices where large diffraction efficiencies are needed.

Fiber-optic temperature sensor based on internally generated thermal radiation.

This paper presents a theoretical and experimental study of a method of sensing temperature with optical fibers with the radiation thermally generated within the fiber. Using quartz fibers it is possible to read temperatures in the range from room temperature to over 1000 degrees C. We have demonstrated operation as low as 135 degrees C using nonoptimum fibers and detectors. The method also allows the determination of the location and length of a hot spot along the fiber. The purpose of this type of sensor is to monitor the development of hot spots in electrical machinery, such as generators and transformers, where conventional measurement techniques cannot be effectively applied. If such optical fibers can be incorporated in the manufacturing process of electrical equipment, these temperature monitors may contribute in avoiding catastrophic breakdown.

Lead (II) halides: A new class of acousto-optic and electro-optic materials

Abstract A novel and potentially useful class of crystals, the lead (II) halides were recognized by A.V. Zamkov et al. [Soviet Phys.-Cryst. 24 (1979) 87] for the acousto-optic and electro-optic and electro-optic devices. Lead bromide, PbBr 2 , is the most highly studied of these and was tested for its acousto-optic properties. The crystal possesses certain properties which are highly desirable for signal-processing applications. For this reason, we have developed a method to purify and grow single crystals of this compound. PbBr 2 crystals up to 26 mm in diameter and several cm in length were grown by the Bridgman method. Purification is complicated by oxidation of PbBr 2 in the presence of traces of moisture. Formation of lead chlorite [ Pb ( ClO 2 ) 2 ], mendipite (Pb 3 O 2 Cl 2 ), plattnerite (PbO 2 ) and mixed oxy halides (Pb 3 O 2 BrCl) were observed due to residual chlorine and oxygen impurities. Mendipite was the major constituent of dark bluish residue formed during the purification by directional freezing.

Optical response of epitaxial and granular films of YBa/sub 2/Cu/sub 3/O/sub 7- delta / at temperatures from 25 K to 100 K

The authors present the results of optical detection in epitaxial and granular films of YBa/sub 2/Cu/sub 3/O/sub 7- delta / at wavelengths of 0.63, 3.39, and 10.6 mu m and at temperatures from 25 K to 100 K. Both types of film exhibit only bolometric detection, with no evidence for nonequilibrium effects in this temperature range. For 0.63- mu m radiation, mechanically chopped at 725 Hz, measurements of a 10*90 mu m/sup 2/ epitaxial bridge yield a bolometric responsivity of approximately 4*10/sup 3/ V/W, and detectivity D* of more than 10/sup 8/ cm square root Hz/W. Granular films biased above their critical current are found to exhibit two-level switching noise, resulting in Lorentzian deviations from an otherwise 1/f noise spectrum. >

Growth and characterization of lead bromide crystals

Lead(II) bromide was purified by a combination of directional freezing and zone-refining methods. Differential thermal analysis of the lead bromide showed that a destructive phase transformation occurs below the melting temperature. This transformation causes extensive cracking, making it very difficult to grow a large single crystal. Energy of phase transformation for pure lead bromide was determined to be 24.67 cal/g. To circumvent this limitation, crystals were doped by silver bromide which decreased the energy of phase transformation. The addition of silver helped in achieving the size, but enhanced the inhomogeneity in the crystal. The acoustic attenuation constant was almost identical for the pure and doped (below 3000 ppm) crystals.