Laser transmission demonstration device

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The laser transmission demonstration device is suitable for the teaching demonstration of high school physics courses, which makes the teaching of laser more intuitive and vivid.

Operating principle: See the following figure for the electrical schematic diagram of the laser audio transmitter. This is a three-stage direct coupling amplifier circuit. VT1 and VT2 are two-stage audio signal voltage amplifiers, VT3 is an audio power amplifier, and the laser emission diode VD is connected in series in the collector circuit of VT3. Its working state is always consistent with that of the power tube VT3. There are two input modes for audio signal: one is that microphone B converts sound into electrical signal and sends it to the base of VT1 via C1 coupling; The other is to connect the audio signal from the "Walkman" or other audio source to the line input end, which is divided by R9 and R10 and coupled to the base of VT2 through C4. In the figure, C2, R2 and C6 form a power decoupling circuit to prevent low-frequency self excitation.

Receiving circuit:

The receiver receives the modulated laser beam sent by the transmitter laser emission tube. The laser beam is not a simple laser beam, but a vibrating laser in step with the audio signal change. The phototransistor VT demodulates the audio signal in the laser beam. After the base plate of the phototransistor is irradiated by the laser audio signal, it will produce a photoelectric effect, which is equivalent to inputting an audio electrical signal at the base of the photodiode: after the audio signal is amplified by the VT2 and VT3 low-frequency voltage, the two power transistors VT5 and VT6 of the power amplifier stage drive the microphone to restore sound.