Abstract: Windshear detector using Rayleigh-backscattered light and a molecular filter for optical discrimination, and frequency locking of a laser, to detect windshear. The windshear detector has a pulsed ring laser that transmits a signal out of the detector and receives reflected backscatter of the transmitted signal. The ring laser is driven with an injection laser. Both lasers are ultimately keyed to the molecular transmission or absorption filter with locking electronics. The received reflected backscatter is detected and processed into a signal that indicates whether there is windshear or turbulence.

Abstract: Apparatus for determining the composition of mercury-cadmium-telluride or other alloy semiconductors by using a four-photon mixing phenomenon. Means are provided for a pair of colinear laser beams of different optical frequencies such that the colinear beams passed through a sample of Hg.sub.1-x Cd.sub.x Te or other alloy semiconductors to produce emissions beams of the original incident optical frequencies and two or more additional optical frequencies formed by an electron spin-flip interaction. A magnetic field means is employed for varying a magnetic field across the sample during passage of the colinear beam from the points substantially below to substantially above the resonant field of the sample to produce a spin-flip signal which has a peak amplitude. Detector means are adapted to receive the emission beams to identify the spin-flip signal peak from which the spin-level splitting factor can be measured. Upon measurement of the spin-level splitting factor, the value for x can be calculated in Hg.sub.