Surface roughness meter

Claim 1

AN OPTICAL ROUGHNESS MEASURING INSTRUMENT FOR MEASURING R.M.S. ROUGHNESS OVER A PREDETERMINED RANGE COMPRISING, IN COMBINATION AND IN OPTICAL ALIGNMENT, A SOURCE OF OPTICAL RADIATIONS, MEANS FOR PRODUCING A BEAM THEREFROM OF SUITABLY LOW DIVERGENCE, A ROUGHNESS SAMPLE HOLDER, MEANS FOR DIRECTING SAID BEAM ONTO THE SURFACE OF THE SAMPLE IN SAID HOLDER AT SUBSTANTIALLY NORMAL INCIDENCE TO PRODUCE A REFLECTED BEAM, MEANS FOR SELECTING TWO NARROW WAVELENGTH BANDS OF THE REFLECTED BEAM, THE WAVELENGTH OF THE SHORTER BAND BEING AT LEAST TEN TIMES AS LONG AS THE MAXIMUM R.M.S. ROUGHNESS TO BE MEASURED, A RADIATION DETECTOR, MEANS FOR IMAGING THE TWO SELECTED NARROW BANDS OF THE REFLECTED BEAM THEREON, MEANS FOR ATTENUATING AT LEAST ONE OF THE NARROW BANDS, MEANS FOR CHOPPING THE RADIATION LOCATED INTERMEDIATE THE LIGHT SOURCE AND THE DETECTOR, MEANS FOR GENERATING A REFERNECE SIGNAL SAID MEANS BEING ACTUATED IN SYNCHRONISM WITH THE CHOPPING MEANS, A PHASE SENSITIVE A.C. AMPLIFIER, MEANS FOR CONNECTING THE OUTPUT OF THE RADIATION DETECTOR TO THE INPUT OF SAID AMPLIFIER, AND MEANS FOR INDICATING POLARITY AND MAGNITUDE OF THE AMPLIFIER OUTPUT WHEREBY SAID MEANS INDICATE A FUNCTION OF THE RELATIVE AMOUNTS OF RADIATION IN THE TWO BANDS STRIKING THE DETECTOR.