Optical measurement device with enhanced sensitivity

An apparatus for evaluating optical parameters of a thin film layer formed on the surface of a sample comprising:

• laser means for generating a probe beam;
• primary lens means for focusing the probe beam to a spot size on the order of micron in diameter on the surface of the sample;
• first detector means for measuring the full power of the reflected probe beam;
• first relay lens means located in front of the detector means;
• and
• first blocking means located between said detector means and said first relay lens means and in the focal plane of the first relay lens means, said first blocking means having an aperture dimensioned to transmit focused light reflecting off the boundaries of the thin film layer and block scattered light reflected from the surface of the sample beyond a first predetermined distance from the center of the focused spot.

An optical measurement device for evaluating a sample comprising:

• laser means for generating a probe beam;
• a lens having an aperture for focusing the probe beam on the surface of the sample, and with the diameter of the probe beam in the plane of the lens being greater than the diameter of the aperture so that the lens is overfilled;
• first detector means for measuring the reflected probe beam and generating a first output signal for evaluating the sample;
• second detector means positioned to receive a portion of the probe beam without passing through the lens or being reflected from the sample, said second detector means for measuring the incident power of the probe beam and generating a second output signal for normalizing the first output signal;
• and
• blocking means positioned in front of the second detector means and having an aperture dimensioned in a manner to restrict the transmission of the probe beam to be equal to the transmission of the probe beam through the aperture of the lens.