Abstract: A vertical curtain is provided with vertical slits therein spaced thereacross, opening downwardly through the lower margin of the curtain and terminating upwardly a spaced distance below the upper margin of the curtain. The upper margin of the curtain is mounted on the margin of a refrigerated cabinet wall having an access opening formed therein extending across the upper portion of the opening such that the curtain will fall by gravity downwardly across the opening as a thermal and convection current barrier when the door for the access opening is opened.

Abstract: Pulse-tone laser radar utilizing an acousto-optic angular multiplexer and frequency shifter. The laser radar includes both a pulsed laser and a CW laser. A portion of the CW laser beam is utilized as a reference or local oscillator. An acousto-optic angular multiplexer passes the output of the pulsed laser when the acousto-optic multiplexer is in its off state and passes and frequency shifts the output of the CW laser when the acousto-optic multiplexer is in its on state. The acousto-optic angular multiplexer is operated to pass a pulse followed by a CW tail to generate the pulse-tone waveform. The return signal from a target is beat together with the local oscillator signal derived from the CW laser. The resulting beat signal includes both range and velocity information.