Abstract: A secure communications system which comprises a laser-sending system and a light receiver. The laser light is divided into two beams, one beam is modulated to add the signal thereto, then the beams are recombined and directed to the receiver. The receiver then separates and demodulates the signal.

Abstract: A method for measuring the separation between two spaced light-reflecting rfaces by means of a single laser pulse. The reflected light is divided into two beams which are then projected at the same angle .theta. onto the same area on a photographic film to form interference fringes. The film is developed, placed on a translating platform, and passed through the beam of a CW laser, a portion of the beam being diffracted by the interference fringes recorded on the film. The distance .chi. between the high-intensity points of adjacent interference regions is measured and the separation of the two light reflecting surfaces is calculated from the formula d=.chi. sin .theta..

Abstract: The invention comprises a method and means for measuring the separation been two optical surfaces. A short-coherence-length laser pulse is projected upon two optical surfaces separated by a distance, d. The reflected, coincident beams are directed into a Michelson interferometer in which one plane mirror is replaced by a stepped mirror. The beams reflected from the two mirrors are directed onto a film where they form interference images. A formula using the number of channels, n, between successive interference fringes and the step width of the stepped mirror is used to calculate d.