US Government As Represented by the Secretary of the Army

Charles R Christensen

Frederick W Clarke

John A Grisham

James L Smith

Carl C Aleksoff

Joseph G Duthie

Joseph K McDonald

Neal C Gallagher

Carl D Leonard

John L Stensby

The device and method for performing an optical Hall test provide means for on-destructive measurement of free carrier concentration or effective mass in semiconductor materials using Faraday rotation spectra. A beam emitted by a Fourier transform infrared (FTIR) spectrometer is transmitted through the sample that is mounted between a polarizer and analyzer and the opposite poles of a magnet before finally being incident on a detector. The ratio of the samples's transmission spectrum with the magnetic field on to that with the magnetic field off is converted, through a suitable mathematical formula, to Faraday rotation. The rotation is, then, plotted versus the square of the wavelength. The slope of the graph at longer wavelengths is directly proportional to the carrier concentration and the effective mass. With one known, the other can be easily determined.

Device and method for performing an optical hall test

A modulated Faraday rotation signal is produced by passing a linearly polarized laser beam through a semiconductor wafer sample in a modulated magnetic field that is induced in an electromagnet by a sine wave generator and driver coupled thereto. The rotation signal is normalized by dividing by a transmission signal produced by modulating the beam with a chopper that operates at a different frequency from the frequency of the driver. The result is a Faraday rotation measurement with high signal-to-noise ratio and compensation for laser drift in intensity.

Modulated high sensitivity infrared polarimeter

A method of copying a thick hologram, recorded at wavelength .lambda..sub.1, so that the copy can be efficiently read out with a beam .lambda..sub.3 at the same incident angle as used to efficiently read out the original. The method involves copying the hologram using wavelength .lambda..sub.2 at a predetermined incident angle, which incident angle provides fringe angles in the copy to yield maximum diffraction efficiency of the read-out beam .lambda..sub.3.

Method of bragg angle adjustments for copying holograms

A beamrider guidance system for missiles wherein a laser beam is given two circular motions around the boresight axis to produce amplitude and phase modulation on the signal received at the missile. The information on distance from boresight is contained in the amplitude modulation and the angular information is contained as phase modulation. A laser optical system with a spinning holographic element provides one of the circular motions for the beam. The other circular motion is provided by a low frequency, circular scanning mirror.

Scanning beam beamrider missile guidance system

A packageable system employs principles of Doppler holography on near-field objects to produce images from which photographs, transparencies or video reproductions can be made with simultaneous improvements in depth of field, foreground-backregion exposure ratio, and resolution (where degraded by the object medium). The apparatus consists of two units: a main unit containing a laser and optics, and an external platform that rotates at an appropriate angular velocity, through a very small arc, during image recording of an object on the platform.

Dopler extended depth of field imaging system with coherent object

The Doppler frequency shift of coherent light reflected from moving objects is used to obtain resolution much greater than the classical limit for imaging systems. The Doppler information is processed by using the temporal and spatial filtering properties of modulated reference wave holograms formed with a reference wave having a range of frequencies across it matching the Doppler frequencies received from the moving object.

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Athens, AL, United States of America

Charles R Christensen