Abstract: There is described an apparatus (2) for measuring an amount of an analyte in a mixture. In one example, the apparatus (2) has a laser source (6) for generating a frequency-modulated laser beam (22). A cavity (36) receives the frequency-modulated laser beam (22) and a photodetector (46) obtains an intensity signal indicative of an interaction between the frequency-modulated laser beam (22) and the mixture. The apparatus (2) has a first demodulator (76) for producing a first demodulation signal. A frequency locking arrangement uses the first demodulation signal to lock a carrier frequency of the frequency-modulated laser beam (22) and a mode of the cavity (36) to each other. The apparatus has a second demodulator (50) for producing a second demodulation signal and for generating, on the basis of the second demodulation signal, an output indicative of the amount of the analyte in the mixture. Other apparatus and methods are described.

Abstract: A light projection apparatus includes a source of unpolarized light. The light passes to a first polarizing means that converts substantially all of the light incident on the polarizing means from the source into polarized light. The first polarizing means is preferably a polarizing cube beam splitter. The light passes to image means, which preferably includes a liquid crystal cell, for generating an image to be projected. A second polarizing means such as a polarizing cube beam splitter is provided optically after the image means for receiving light passing through the image means and passing a first beam having a first planar polarization and deflecting a second beam having a second planar polarization, at least one of the first and second beams providing a projected image.