Abstract: An apparatus for generating a pulse-like constant current with a variable pulse width for use in evaluating thermal characteristics of a laser diode.

Abstract: An apparatus for measuring a radiation characteristic of a laser diode. An AC signal and a step-like DC voltage are applied to the laser diode and the radiant power output thereof is received by a photodiode having an output to which a first amplifier, a transformer, a capacitor and an AC amplifier for extracting the AC signal. The apparatus further comprises a first switch connected between the input of the first amplifier and the capacitor, and a second switch connected between both ends of the transformer. Every time the step-like voltage is stepped up, the first and second switches are closed for a short time as compared with the duration of a step period to protect the measurement from the influence of the change in the DC voltage.

Abstract: An electrostatic voltmeter for measuring the surface potential of a charged body, includes a detecting electrode locatable adjacent to the charged body, and a vibrating element having a pair of parallel spaced legs between which the detecting electrode is disposed in spaced relation. The vibrating element is vibratable such that the legs move toward and away from the charged body. The vibrating element may extend transversely or parallel to a line connecting the charged body and the detecting electrode.