[time-nuts] Pressure sensitivity of Rb vapor cell standards

[Bruce Griffiths]

The wavelength of a laser diode can be tuned by varying its temperature and/or bias current.
Mode hopping during tuning can be an issue with standard FP laser diodes.
Single transverse and longitudinal mode operation is also desirable.
The laser wavelength has to be within a few picometers of the absorption line center before it can be served to the absorption line center. Typically longitudinal modes have a separation of a few tenths of a nanometer for FP laser diodes. AR coated laser diode chips with an external cavity are easier to tune without mode hopping.
A cateye resonator with a tilt tuned narrowband filter is easier to align than a Littrow or a Littman-Metcalf resonator.

VCSELs and DFB (with integral Bragg grating) can be better behaved but stabilising the polarisation mode is desirable for a VCSEL otherwise polarisation mode hopping can occur.

Bruce
> On 20 February 2020 at 10:29 Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
> 
> > You will not be able to find one with the correct wavelength. An unstabilized
> > laser diode has an output bandwidth in the 50-300MHz range. Which means you
> > need to hit the right wavelength with the accuracy of the bandwidth of the
> > laser. For a bandwidth of 100MHz at 780nm that means you have to hit the
> > right wavelength with an accuracy of 0.2pm. The slightes vibration, the
> > slightest change in temperature, the slighest change of current through the
> > laser diode or a fly coughing and you are off. That's why you have to
> > actively steer the laser diode such that its output wavelength stays where
> > you want it to be. If you are using a laser, there is no way around it. 
> 
> What parameter do I adjust if I want to steer a laser?
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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