text: The conventional photo-reflectance experimental setup uses a xenon or tungsten based lamp source passed through a monochromator to form the incident probe beam.  The pump beam may be formed by the output of a continuous wave (CW) laser (e.g. a He-Ne or He-Cd laser) passed through a chopper wheel, or may be formed by the output of a directly modulated semiconductor diode laser. The pump beam is focused to a spot on the sample where it interacts with the sample. The probe beam is co-focused onto the sample where it is reflected.  The reflected probe beam is collected and passed through an optical filter to eliminate any unwanted pump light and/or photoluminescence signal.  Thereafter the probe beam is directed onto a photodetector (e.g. a Si or InGaAs photodiode), which converts the probe intensity to an electrical signal. The electrical signal is processed to eliminate unwanted noise, typically using a lock-in circuit referenced to the modulation frequency.  The photo-reflectance signal is then recorded as a function of probe beam wavelength using a computer or the like.