Selective Meter of Photomultiplier Currents for the Magnetic Circular Dichroism Spectroscopy in Reflected Light
摘要
A relatively simple circuit of a selective meter of constant and variable components of the total current of a photomultiplier when recording magnetic circular dichroism spectra in reflected light using the method of light-wave phase modulation with the help of a photoelastic modulator is presented. The circuit implements a method for measuring the photomultiplier anode current using a load resistance RL and a buffer preamplifier. The variable current component is extracted via compensation of the constant component of the total signal. The experimental techniques are described that make it possible to determine the optimal RL value for which the influence of the input shunt capacitance is minimal in the frequency band of ~100 kHz. The main source and level of the parasitic photocurrent not associated with the incident monochromatic radiation are determined. The meter testing showed high efficiency of its use in magnetic circular dichroism spectroscopy. An algorithm for spectrum recording is proposed taking the change in the circular dichroism effect polarity into account. The performance and efficiency of the developed meter are illustrated by an example of measuring the magnetic circular dichroism spectrum of a GaMnAs film.