Re: Single mode laser from a multi mode diode laser, how?

alex <aesbrown@xxxxxxxxxxx> writes:

The submodes of the TEMXY will in general have different frequencies and/or
phase. The frequency difference will be much less than the longitudinal
mode spacing. For example, a laser with GHz longitudinal mode spacing
may have transverse modes differing by a few MHz.

Well I thought I had better up date you.... To eliminate the
possibility of ghosting in the etalon due to misalignment, etc I
cleared the whole bench and just had the diode and two mirrors to
guide the beam into the Melles griot spectrum anaylser... After
aligning everything perfectly I was getting back refkection into the
diode laser and chaotic behaviour ensued. The back reflection didn't
matter previously as the light had already been through two BS before
entering the spectrum analyser...

After inserting the ND filter and slighlty misaligning the setup it
appears that the diode laser is mutli mode. With 200 MHz of jitter,
which has now become a concern. The modes are so close together that
to be honest I'm just going to pick the middle mode and use a large
error to include the other modes...

Can you take some photos of the display?

When you say multimode, do you mean longitudinal (100s of GHz spacing) or
spatial (much closer). A multi-spatial mode low power diode would be
unusual. (What is the maximum spec'd power for the diode?)

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My only hope that the modes are seperated by such a short gap that
they cannot excite to different vibrational modes in the excited
electronic state... I must check that tmrw..

Thanks for everyones help and suggestions... I think this absorption
spectroscopy might work....

ALex
.

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