dedicated analog to digital converter so as to minimize integration time and add speed to the data analysis without signal degradation the microprocessor provides digital data such as measurement data and analyzer status information to one or more external devices in a preferred embodiment of the invention the analyzer also employs in situ physical presentation of data which can be monitored without an external device a schematic representation of another preferred embodiment of the invention is shown in fig2 optical radiation is generated by laser source 212 the radiation source is temperature controlled by laser cooler 214 and the radiation is shaped spatially and spectrally by beam shaping optics 213 which in one preferred embodiment include lenses to control the spatial extent and collimation of the beam a wavelength selective reflecting element to control and stabilize the central wavelength of the beam and optical filters to limit the spectral extent of the beam the temporal characteristic of the laser radiation is controlled by laser controller 211 which in turn is controlled by control microprocessor 250 in one preferred embodiment the temporal characteristic of the beam incorporates a boxcar modulation at a frequency below 10 mhz to facilitate discrimination against stray optical background the laser source 212 laser cooler 214 beam shaping optics 213 and laser controller 211 are included in radiation module 210 upon leaving the radiation module the laser radiation enters the free space optics module 220 the free space optics module includes a selective reflector 222 with a large clear area and a small reflective area in.