The present invention includes a method of changing intensity of a reflected beam which may be expressed as a method of changing the amount of reflected light from a beam of light, the method comprising: (a) providing a substrate bearing a film of a reflective material; (b) directing a first beam of light at a reflecting point upon the reflective material so as to create a reflecting beam therefrom; (c) directing a second beam of light at the reflecting point upon the reflective material so as to alter the amount of light in the reflecting beam, and (d) detecting the change in the amount of light in the reflecting beam. The invention also includes an apparatus for changing the amount of reflected light from a beam of light and measuring that change, as well as related apparatus for providing a pulsed optical signal by changing the amount of reflected light from a beam of light.