Abstract
In this paper we consider a new type of mechanical device for periodic modulation of laser radiation. The modulating unit consists of two phase diffraction gratings with a rectangular profile, one of which moves relative to the other. The output beam of radiation in this device can be either a zero-order beam of diffraction, or one of the first orders of diffraction. The results of numerical simulation of output waveforms are presented. In the first order, we obtain a sinusoidal form of output power modulation with an efficiency of up to 40 percent. Optimal parameters of the phase diffraction gratings are calculated. Modulation produced in the zero order of diffraction has an impulse form with an efficiency of about 80-90 percent. The specific shape of the pulses in the zero order of diffraction depends on the distance between the two gratings. The results of numerical calculations and experimental studies are in good agreement. A special advantage of this type of modulator is the possibility of increasing the frequency of mechanical modulation of the laser beam to hundreds of kHz. The results of experimental studies of the characteristics of the scheme under consideration are presented. The device makes it possible to obtain modulation frequencies up to hundreds of kHz with a harmonic waveform in the first orders of diffraction and periodic pulses in the zero order.
Highlights
Optical choppers are widely used during physical experiments
When the laser beam intersects the borders of holes, diffraction effects occurs, which distort a shape of the output beam
We present results of investigations of the device where laser beam modulation occurs as a result of sequential diffraction by two phase diffraction gratings, one of which is being moved relatively to the other one in the direction across grating lines
Summary
Optical chopper is a rotating disk punctuated with holes or slits Since this type of laser modulator is mechanical in nature, the maximum frequency is limited to the several kHz. In addition, when the laser beam intersects the borders of holes, diffraction effects occurs, which distort a shape of the output beam. There are specific diffraction gratings which have a rectangular “meander” type profile formed by a relief on a transparent substrate used in this device With applying of this device it is possible to increase the frequency of modulation of the laser beam up to hundreds kHz. In the special case, when we use the first diffraction order as output beam, it is possible to obtain its power modulation according to the harmonic law.
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