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

alex <aesbrown@xxxxxxxxxxx> writes:

On 19 Aug, 13:25, Sam Goldwasser <s...@xxxxxxxxxxxxxxxxxxxx> wrote:
alex <aesbr...@xxxxxxxxxxx> writes:
If you have some optics and mechanical skills, you *might* be able to
cobble together a tunable diode laser using your diode and a small
external grating. These aren't all that hard to make -- tons of
graduate students who need a tunable diode laser "roll their own" in
research labs (or even student labs); and you can dig into the
literature for info on how to do it (don't ask me, I don't know how to
do it, just that it is commonly done). If you can do this, you can end
up with a useful and fairly widely tunable optical source.

Well have had a look at doing this and I think they are called
external cavity diode lasers... There are two types Littrow and .....
It would seem that I would need a diffraction grating mounted on a
pizo electric adjuster. I would need to build some (feedback?)
electronics to keep adjusting the lenght of the cavity over a very
short time...

Also, by the looks of it I would need to coat one end of the diode
laser to stop it acting as a cavity and just have it as a gain
medium...

Am beginning to learn the life is not simple where optics is
concerned.... :) Time for a rethink, as time is of the essence....

From what Sam said the chance of buying a single mode diode laser is a
matter of luck than anything else? Or do places sell them
specifically as such?

Thanks
ALex
I have the diode laser (Roithner) temperature controlled and current
controlled, but getting a single mode over the range that I see
flourescnece occuring in the Iodine cell is proving troublesome. When
I scan ofrom 40 to 50 mA I see loads of flouresence, but over this
range I can't measure the wavelength of the laser :(. I am doing
absorption spectroscopy, but using flouresence to indicate absortion
occuring.

It may be worth asking on alt.lasers or a forum specifically for holography.
There are also laser diode kits sold for holography. Of course, there may
be no way to know if a single mode stable point will coincide with an I2
absorption line.

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Thanks Sam,

I have asked on alt.lasers and will wait and see.

On a different note I thought the only important criteria for
holography was for the coherence lenght to be reasonably long for good
interference fringes. Why must the laser be single mode?...

Because there's no way to get a long coherence length with a multimode
diode. :)

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