The green laser I am using normally consumes 400mA while the lowest operating current is about 250mA. The potentiometer on the base of the transistor is used to control DC offset, while the second potentiometer is used to control "volume". The 10k resistor is a pull down resistor.
The laser has current limiting with a maximum voltage of 5V so if the sine wave where to exceed the 400mA it would be cropped, increasing the distortion. This in fact is a class A amplifier. The receiving side can be a solar panel connected to an amplifier or a photoresistor in series with a battery.
