Showing papers on "Signal beam published in 1977"

Laser controlled optical switching in semiconductors

Abstract: A method and apparatus for switching an infrared radiation signal laser beam in which a semiconductor, capable of transmitting the signal beam without damage, is provided and upon which the signal beam is incident at an angle which may preferably be Brewster's angle. The surface of the semiconductor is irradiated by a second laser beam which has a sufficiently high frequency to produce free carriers in the semiconductor and which has a sufficient radiation intensity and time duration to produce a free carrier density greater than the critical density for the signal beam resulting in substantially total reflection of the signal beam from the semiconductor surface. In particular, a pulsed CO 2 laser beam which is incident on a polycrystalline n-type germanium semiconductor is reflected by irradiating the semiconductor with a pulsed ruby or Nd:glass laser beam.

Holographic interferometry with increased sensitivity for diffusely reflecting objects.

Abstract: The reconstructed image of a double exposure hologram, made by deforming the object and slightly tilting the signal beam at the same time, consists of modulated Young’s fringes. It would be possible to presume the plate, which is used for taking a photograph of the reconstructed image and is processed in a nonlinear way, to be equivalent to a nonlinear hologram. Therefore the principle of phase difference amplification applies. Thus the interferogram with increased sensitivity of λ/16 per fringe was experimentally obtained with a diffusely reflecting object. Discussions of the system error are presented.

Depolarization measurement by optical heterodyne

Abstract: A sensitive, noise-free ellipsometer measures depolarization of an incident beam by forming from the reference and signal components of the incident beam a signal component polarized in one direction, and a frequency shifted local oscillator component polarized in the same direction, with these latter components being optically heterodyned at a detector. In the formation of the local oscillator component, the reference component of the incident beam is shifted in frequency from that of the signal component of the incident beam and rotated 90° from its original orientation so that optical heterodyning can take place. This is accomplished by passing the incident beam through a shear-wave, traveling wave acoustic modulator which forms local oscillator and signal beams, each having rotated and frequency shifted components, and unrotated and unshifted components. Thereafter, all the light from the modulator is incident on a polarization analyzer which selects for heterodyning the unshifted, unrotated components of the signal beam and shifted, rotated components of the local oscillator beam. The shear wave action of the modulator operates to provide the rotation, while the traveling wave action of the modulator assures that the frequency shift is in only one direction.

Crystal Streak Camera

Abstract: A high speed optical deflection system has been designed for picosecond laser pulse diagnostics. Evaluation of a prototype system indicates that an ultracompact streak camera with picosecond resolution can be constructed from readily available components with a relatively low cost. A commercially available electro-optic beam deflector with a 2-mm aperture ADP crystal is used in the prototype. This unit is capable of deflecting wavelengths from the visible to 1.06 pm. When high power single picosecond pulses are used, previous limitations of electro-optic deflectors due to signal beam absorption, internal heating, and mechanical shock waves are overcome. At 532 nm, a resolution of 18 spot diameters is obtained, while the dynamic range in excess of 200 is limited by the readout system. Use of a crystal material with a much higher electro-optic coefficient produces a theoretical resolution c,omparable to that of electro-optic cameras. The high current required to drive the crystal presents some difficult electronics problems and available solutions are discussed. Readout is accomplished with film, a TV camera, or a linear diode array. Computer manipulation of the output data can be used to improve resolution and dynamic range.

Birefringence effects in estar base reconnaissance film in an optical correlator

Abstract: Coherent optical correlators using Fourier transform matched filters are generally constructed using the interference between a transformed signal beam and an equipolarized collimated coherent reference beam. Polarization effects of any system elements must be accounted for in using such a correlator, or in any system using holographic techniques, particularly if analysers are used. Birefringence effects of estar base film, used almost exclusively in aerial reconnaissance work, have been examined by the authors when such film is placed in the signal path. Methods of compensation for such effects are suggested.

Formation of a holographic beam splitter in an optoelectronic holographic memory system

Abstract: A raster of holographic beam splitters was recorded directly in the optical system of a holographic memory. The aberrations of an objective lens, distorting the structure of the signal beam, were corrected.