Patent ID: 7920265

Claim:
Laser noise suppression apparatus for a modulated optical reflectance (MOR) system including a pump laser configured to generate a modulated beam that is directed at a surface portion of a sample for exciting said surface portion, a probe laser configured to generate a non-modulated beam, and a beam splitter configured to split the non-modulated beam into a first portion and a second portion, said laser noise suppression apparatus including: a first detector configured to receive the first portion of the non-modulated probe laser beam to produce a first signal corresponding to the first portion; a second detector configured to receive a reflected part of the second portion of the non-modulated probe laser beam that has been reflected from said surface portion, wherein the second detector is configured to produce a second signal corresponding to the reflected part of the second portion; a signal combiner having first and second inputs and an output, wherein the first input is configured to receive the second signal, wherein the signal combiner is configured to produce a combiner signal at the output that corresponds to a difference between signals applied to the first and second inputs, a level balancer configured to receive as inputs the first signal and a signal derived from the combiner signal and produce a balancer output that is coupled to the second input of the signal combiner, wherein the level balancer and signal combiner are configured such that combination of the balancer output and the second signal tends to cancel out an average value of the second signal from the combiner signal.