Abstract: A focus error signal resulting from the photothermically-induced expansion is measured in a sample of material under analysis. A laser is disposed as a periodically modulated heating source which is directed to the sample and a device for focus error measuring which is directed to the surface being heated. A device measuring focus error generates a signal representative of the displacement of the surface of material in perpendicular direction due to the expansion produced by the periodic heating, which is filtered, either analogically or digitally, to discriminate the displacement component at the frequency in which it was modulated or at any other related frequency, such any harmonic or a sum with any other modulation. The focus error signal, appropriately calibrated, gives a precise and sensitive measure of the magnitude the expansion.

Abstract: A focus error signal resulting from the photothermically-induced expansion is measured in a sample of material under analysis. A laser is disposed as a periodically modulated heating source which is directed to the sample and a device for focus error measuring which is directed to de surface being heated. A device measuring focus error generates a signal representative of the displacement of the surface of material in perpendicular direction due to the expansion produced by the periodic heating, which is filtered, either analogically or digitally, to discriminate the displacement component at the frequency in which it was modulated or at any other related frequency, such any harmonic or a sum with any other modulation. The focus error signal, appropriately calibrated, gives a precise and sensitive measure of the magnitude the expansion.

Abstract: The invention is an apparatus that measures dirt density on steel plates, characterized by including a pulsed laser that impinges on the inspected plate, and a microphone that detects the sound produced by the sudden ablation of the dirt, the amplitude of the microphone signal being the measure of the dirt on the plate. The microphone is connected to an electronic signal processing system, which is a computer or a programmed digital processor that determines the average value and standard deviation of the signal over the number of hits specified by the operator.

Abstract: The invention is an apparatus that measures dirt density on steel plates, characterized by including a pulsed laser that impinges on the inspected plate, and a microphone that detects the sound produced by the sudden ablation of the dirt, the amplitude of the microphone signal being the measure of the dirt on the plate. The microphone is connected to an electronic signal processing system, which is a computer or a programmed digital processor that determines the average value and standard deviation of the signal over the number of hits specified by the operator.