After every laser there is an optical isolator that ensures the laser light cannot re-enter the laser, if reflected and sent back.
What would actually happen if this were to happen? Would the laser break because of too much power?
[Physics] n’t we shine laser light back into the laser
laseroptics
Best Answer
Its not true that feedback is detrimental to all laser systems. In fact, some laser systems rely on it heavily for frequency control. Specifically, diode laser systems in the Littrow Configuration use feedback from a diffraction grating in order to stimulate emission in the laser cavity at the wavelength specific to the first order of diffraction. Tuning the angle of the grating with a piezo electric device allows for precise frequency control of the laser. Other diode lasers, such as AR coated diode lasers rely on optical feedback in order to have enough light in the cavity to lase.
With that being said, optical isolators are still a good idea after the laser head output because back reflections from the optics downstream can cause optical feedback that cause the laser to lase in a mode that you don't want. This can produce laser frequency noise and mode hops which will ruin the operation of the laser, but won't necessarily cause physical damage. However, some diode chips have a maximum power threshold, and too much feed back (perhaps direct feedback with a mirror and the laser at full current) can damage the chip.