ON ANALYSIS OF SIGNALS FROM A PHOTOTHERMAL MICROSCOPE

The potential of the photothermal microscope using a photodiode (mono- cell) to detect a probe beam is analysed and an expression derived to evaluate the influence of variation in thermal parameters with tempera ture on the photothermal signal. The sensitivity of the photothermal m icroscope (about 5 x 10(-3)-degrees-C) limited by quantum noise is dis cussed. Deflection of the probe beam by deformation of the surface cau ses an additional modulation of the probe beam because not all of the reflected light passes back through the microscope. The analysis shows that, especially for metals, this can produce a signal, the magnitude of which is comparable to that of the photothermal signal.