Patent ID: 7068362

Claim:
An apparatus for determining a beam attenuation coefficient of a medium, comprising: a signal source that generates a generated optical beam; a first arrangement that collimates the generated optical beam to form a projected optical beam; a retroreflector that directs the projected optical beam; a second arrangement that receives the projected optical beam from the retroreflector and that focuses the projected optical beam to form a focused optical beam; a detector that detects a portion of the focused optical beam in order to produce an electrical signal so that the beam attenuation coefficient can be determined; a synchronizer that causes the signal source to generate the generated optical beam in a pulsed pattern and that causes the detector to detect the portion of the focused optical beam in concert with the pulsed pattern; wherein the signal source comprises a light emitting diode (LED) and wherein the synchronizer comprises: a timer that causes the LED to generate the generated optical beam in concert with a pulse rate; a lock-in amplifier tat processes the electrical signal in concert with the pulse rate, whereby an effect of distortion that is incurred by the generated optical beam traversing between the LED and the first arrangement, by die projected optical beam traversing between the first arrangement and the second arrangement, and by the focused optical beam traversing between the second arrangement and the detector is ameliorated.