Re: Diode Laser, Quarter Wave Plate and a Linear Polariser

alex <aesbrown@xxxxxxxxxxx> writes:

Right. This works as long as the backreflected light changed its (circular)
polarization.

You mean that the reflection off say a lens must change the
polarisation of incident light?
So that the lhs circularly polarised light created by the QW plate
becomes RHs circularly polarised on reflection?

I am sorry I reall am struggling with picturing what is happening.
Can you walk though what is happening to the beam as it goes through
the devices. I am very new to all of this.

I think from what you say I have diode laser, QW plate and then linear
polariser in that order. Is that right? What anlge is the linear
polariser placed at wrt to the linear polarisation dirction of the
diode laser?

Sorry for such basic questions
ALEx

Diode laser -> linear polarizer or PBS -> QWP

The linear polarizer or PBS (polarizing beam splitter) is lined up to
pass the output of the diode laser. The reflected beam will be
orthogonally polarized after passing back through the QWP so it won't
get through.

Note that with the typical polarizer, this won't be perfect.

Your first line of defense should be to arrange any potentially optical
surfaces to not reflect light directly back to the diode laser.

Where this isn't possible, minimizing backreflections is critical,
an optical isolator may be required.

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