Showing papers on "Signal beam published in 1968"

Electromagnetic energy logic employing saturable absorbers

Abstract: Control beams of electromagnetic radiation are applied to a member of saturable, energy-absorbing material to control the transmission of a signal beam therethrough. Incoherent beams on different volumes of material accomplish a threshold gate logic function, and similar beams on a common volume accomplish the OR logic functions. The use of coherent control beams produces an interference pattern of alternate bands of saturated and absorbent material, which pattern attenuates the transmission of the information beam through the material even though each control beam is of sufficient intensity, when acting alone, to saturate the material so that it is essentially transparent to the signal beam. Information signal transmission occurs as an EXCLUSIVE OR logic function of the coherent control beams, and such function is extendable for generating a logical NEGATION function and for complementing the information in a photographic transparency.

Optical sampling of subnanosecond light pulses

Abstract: In this paper we shall describe a technique for the display of subnanosecond light pulses which is the optical analog of the technique used in electronic sampling oscilloscopes. The optical pulse waveform to be displayed is assumed to repeat itself with period T. A mode-locked laser provides a source of sampling pulses of a few picoseconds duration. The period of this laser is adjusted to be T + δT, where δT s is proportional to ∫ I 1 I 2 dt, where I 1 and I 2 are the intensities of the light signal beam and sampling beam, respectively. If the signal beam is slowly varying compared to the very brief sampling pulse, we have: Y s = constant × I 1 (t n ) where t n is the arrival time of the nth sampling pulse at the nonlinear crystal. Because of the slightly unequal periods, the sampling pulse scans the light signal in steps of δT seconds. Displays of the sum frequency signal Y s on a conventional oscilloscope therefore constitute a sampled display of the light signal. In an experiment to test the method, sampled displays of subnanosecond pulses generated by a mode-locked He-Ne laser (wavelength 0.633µ) were obtained. The source of sampling pulses, ∼4 psec in duration, was a mode-locked Nd:glass laser (wavelength 1.06µ). The two unfocussed beams were mixed in a KDP crystal and the sum frequency signal at 0.397µ was detected by a photomultiplier and displayed on an oscilloscope. The period T of the He-Ne laser pulses was 12.44 nanoseconds, and the sampling step δT was varied between 100 psec and 400 psec. Using this method the He-Ne laser pulse width was observed to vary between 700 psec and 900 psec depending on the He-Ne laser adjustment. These measurements were confirmed with a fast photodiode and an electronic sampling oscilloscope. The average He-Ne laser power was ∼1 mw. In the KDP crystal the sampling pulses converted red light into UV light with an efficiency of about 5%. Since with focussed beams an efficiency of better than 20% can be achieved, it appears possible to optically sample light signals with average powers much less than a milliwatt.

Information in Noisy Photon Beams

Abstract: The fluctuations in a thermal beam due to the superposition of two similar thermal beams are computed. The information loss due to superimposing a quasi-monochromatic thermal-noise beam on a similar signal beam is investigated for two types of noise beams, sample noise, and path noise. In the Wien and Rayleigh–Jeans limits, the information loss j23 per macrocell is found to depend only on the signal-to-noise ratio. The relative loss in maximum obtainable information, I3,max/I2,max, for given signal and noise beams is given as well as some numerical examples.