Pockels cell voltage probe for noninvasive electron-beam measurements

Accurate measurements of beam position and current are critical for the operation of the high-energy electron accelerators used for radiographic applications. Traditional short-pulse (e.g., 70 ns) machines utilize B-dot loops to monitor these parameters with great success. For long-pulse (e.g., 2 mus) accelerators, beam position and current measurements become more challenging and may require new technology. A novel electro-optic voltage probe has been developed for this application and provides the advantages of complete galvanic isolation, excellent low-frequency performance, and no time integration requirement. The design of a prototype sensor is presented along with preliminary accelerator test data.     

On the etalon effect generated by a Pockels cell with high-quality antireflection coatings

We discuss the modulation in the spectrum generated by the windows of a Pockels cell. Although they are antireflection coated, the residual reflectivity of the highly parallel window faces can still have etalon effects that lead to pronounced spectrum modulation. This problem is easily solved by the use of slightly wedged windows.     

High-contrast, all-optical switching in bacteriorhodopsin films

We report experiments with nonlinear-absorption-based, high-contrast, all-optical switching in photochromic bacteriorhodopsin (BR) films. The switching action is accomplished by control of the transmission of a weak probe beam through a BR sample with the help of strong pump beam illumination at 532 nm wavelength. We found that the switching properties of BR films depend on several experimentally controllable parameters such as probe wavelength, pump beam intensity, and excitation rate. A comparative study of the switching behavior and other parameters of practical use was carried out at three probe wavelengths (543, 594, and 633 nm) and various beam powers and pump excitation rates. The results are presented for commercially available wild-type and D96N variant BR films.     

Design and performance characteristics of an electromagnetic interference shielded enclosure for high voltage Pockels cell switching system

An electro-magnetic interference noise shielding enclosure for Pockels cells for high speed synchronized switching has been set-up and tested. The shielding effectiveness of the aluminum enclosures housing the Pockels cells and the electronic circuitry has been measured using a high impedance probe and is found to be ∼50 dB. This ensures a noise-free and synchronized electro-optic switching in an Nd:glass re-generative amplifier of chirped pulse amplification based table top terawatt laser system. resigned from RRCAT     

Design and optimization of a low-frequency electric field sensorusing Pockels effect

The present paper proposes an optical device for measuring low-frequency (50-60 Hz) high electric fields (0-200 kV.cm^-1) using a LiNbO₃ crystal as sensing medium without any contacting electrode. Thus, a good galvanic insulation of material and person is obtained. An experimental setup is developed in the laboratory by using the electro-optical effect or Pockels effect, and several measurements are realized. Simulations are performed with the finite element method (FEM) to optimize the sensing medium of the device. Experimental and simulation results are presented and discussed. The sensor induces a weak disturbance of the local electric field to be measured. The sensibility of the sensor is about 4 μA/(kV.cm^-1 )     

Complete polarization conversion using one crystal with dual transverse Pockels effect

Based on dual transverse Pockels effect, complete polarization conversion can be achieved by using only one electro-optic crystal and its two externally applied voltages. The electro-optic phase retardation and the azimuth angle of the field-induced principal dielectric axes of the crystal can be independently and linearly controlled by the amplitude and direction of the applied electric field, and the formulas for this correlation are deduced for arbitrary input and output polarization states. The candidate crystals mainly include the uniaxial crystals of 3 m, 62 m, and 32 symmetry groups, and the cubic crystals of 43 m and 23 symmetry groups. Theoretical analysis demonstrates that one crystal exhibiting both dual transverse Pockels effect and optical activity can also be used for complete polarization converter. The continuous polarization rotation of a linearly polarized light from 0 degrees to 180 degrees has been performed experimentally by use of single lithium niobate crystal with four lateral electrodes. In addition the light beam position-dependent polarization conversion by using a bulk electro-optic crystal is also measured in the experiment. This new type of polarization converter will have potential applications in many fields due to its simple configuration, explicit control logic of polarization conversion, and lower power consumption.     

High-contrast saturated absorption spectrometer with a grating reflector as an optical frequency locker

By optical feedback of signals obtained with a high-contrast saturated absorption spectrometer as a reference frequency selector, diode laser frequency has been locked to the hyperfine transition line of a Cs atom. We used a grating instead of a mirror for optical feedback to avoid feedback of unwanted modes, because such modes cause mode hopping or generate another frequency component, whose intensity does not decrease even after it passes through an atomic cell twice. Long-term frequency stability has been improved by compensating the cavity length for phase fluctuations.     

Enhanced absorption and electro-optic Pockels effect of electrostatically self-assembled CdSe quantum dots

The spectrum and electro-optic properties of CdSe quantum dots are studied. Spectrum wavelength shifts that are due to the quantum size effect and to the electro-optic Stark effect are investigated. It is found that CdSe quantum dot-polymer composites formed by an electrostatic self-assembly (ESA) technique exhibit high internal electric fields. Using the second-order perturbation theory of the 1s-1s energy shift (Stark effect), we estimate the internal field of the ESA film to be as high as 2.6 x 10(8) V/m. This value results in a much higher absorption coefficient and electro-optic coefficients for ESA films than for their bulk crystal counterparts or for spin-coated film samples. The relationships among unusual spectra, film structure, and high electro-optic response are analyzed. These results are useful both for understanding the physical mechanisms of semiconductor quantum dots and for developing high-performance photonic devices.     

High-contrast images of semiconductor sites via one-photon optical beam-induced current imaging and confocal reflectance microscopy

We demonstrate a computationally efficient procedure for determining only the semiconductor sites in a confocal reflectance image of an integrated circuit. It utilizes a one-photon optical beam-induced current (1P-OBIC) and confocal reflectance images that are generated from the same focused excitation beam. A 1P-OBIC image is a two-dimensional map of the currents induced by the beam as it is scanned across the circuit surface. A 1P-OBIC is produced by an illuminated semiconductor material if the excitation photon energy exceeds the bandgap. The 1P-OBIC image has no vertical resolution because the 1P-OBIC is linear with the excitation beam intensity. The exclusive high-contrast image of semiconductor sites is generated by the product of the 1P-OBIC image and the confocal image. High-contrast images of the metal sites are also obtained by the product of the complementary OBIC image and the same confocal image.     

High-contrast fast Fourier transform acousto-optical tomography of phantom tissues with a frequency-chirp modulation of the ultrasound

We report new results on acousto-optical tomography in phantom tissues using a frequency chirp modulation and a CCD camera. This technique allows quick recording of three-dimensional images of the optical contrast with a two-dimensional scan of the ultrasound source in a plane perpendicular to the ultrasonic path. The entire optical contrast along the ultrasonic path is concurrently obtained from the capture of a film sequence at a rate of 200 Hz. This technique reduces the acquisition time, and it enhances the axial resolution and thus the contrast, which are usually poor owing to the large volume of interaction of the ultrasound perturbation.