Method and apparatus for optically detecting surface states in materials

An apparatus for obtaining information useful for evaluating surface states in a sample comprising:

• means for inducing a periodic, localized excitation at the surface of the sample;
• probe means for emitting a beam of radiation;
• means for directing the beam from the probe means within the periodically excited region on the sample surface;
• means for detecting the periodic changes in the probe beam after it has interacted with the sample;
• means for processing the detected changes that are synchronous with the periodic excitation and generating a signal corresponding thereto;
• and
• means for monitoring the variation of said signal as a function of time to provide information which can be used to evaluate the defect surface states of the sample.

An apparatus for obtaining information useful for evaluating surface states in a sample comprising:

• a pump laser for emitting a beam of radiation;
• means for intensity modulating the pump beam;
• probe means for emitting a beam of radiation;
• means for focusing the intensity modulated pump beam and the probe beam to a localized spot on the surface of the sample such that the pump beam periodically excites the sample surface and the probe beam is specularly reflected;
• means for detecting the periodic changes in the power of the reflected probe beam;
• means for processing the detected changes in the power of the probe beam that are synchronous with the frequency of the modulating means and generating a signal corresponding thereto;
• and
• means for monitoring the variation of said signal as a function of time to provide information which can be used to evaluate the defect surface states of the sample.