[time-nuts] Re: Testing replacement lamps for HP5065A

[Bruce Griffiths]

Some anamorphic beam shaping via a prism or equivalent may be required for efficient use of the laser output.
The datasheet indicates that they are not truly longitudinal single mode except at a particular junction temperature which varies from one chip to the next.
Using some external feedback from an external cavity may be useful in stabilising operation on a single mode without mode jumps. Typical mode spacing appears to be somewhere around 0.5nm or so.
Random mode jumping to a wavelength 0.5nm or so from the desired wavelength will likely impact operation as a pump diode. Careful selection of laser diode, its temperature and excitation current will be required for successful operation.

Bruce
> On 19/09/2022 03:05 Stephen C. Menasian via time-nuts <time-nuts at lists.febo.com> wrote:
> 
>  
> As a bit of background - When I was an undergraduate, I worked with a
> group using optically pumped 87Rb to orient hydrogen via spin exchange to
> measure the hydrogen hyperfine frequency. At that time, our Rb lamps were
> RF excited 1 cm dia spherical bulbs. There was a bit of black magic in
> the choice and type of noble gas used to maintain the discharge. Rb vapor
> pressure was controlled by bulb temperature. I don't believe there was
> any teflon coating in the lamps; teflon coating was used, however, in the
> optical pumping cell to reduce collisional disorientation and consequent
> broadening. At that time we used circular polarizers to achieve the
> pumping effect. I note that the SRS Rb standard uses intensity pumping,
> which I consider cruder.
> 
> I note that Laser diodes in the correct wavelength range are available
> for under $20.00 (Rohm RLD78NZM5 and similar) from Digikey and Mouser.
> These have 10 mW optical single mode output. Most laser diodes are easily
> tuned over a small range; the well defined beam and its polarization
> characteristics could provide a significant advantage over a gas
> discharge lamp. Intensity stabilization would probably be necessary to
> achieve the low noise level necessary for optical pumping. These laser
> diodes include an integrated photodetector to facilitate stabilization.
> 
> Anyway, it might be worth looking into them as lamp replacements.
> 
> Stephen Menasian
> 
> On Fri, 16 Sep 2022 22:59:22 +0200
> Ke-Fong Lin via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> > Hi Corby,
> > 
> > It seems that all the lamps tested are from used rubidium standards.
> > Is it possible to buy "off the shelf" rubidium lamps somewhere?
> > Or is it so "specialized" that's only way to obtain them?
> > Thank  you.
> > 
> > Best regards
> > 
> > On Thu, Sep 15, 2022 at 10:53 PM Corby Dawson via time-nuts
> > <time-nuts at lists.febo.com> wrote:
> > >
> > > Here are details on some tests I ran on replacement lamps for the
> > > HP5065A.
> > >
> > > Cheers!
> > >
> > > Corby_______________________________________________
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> > 
> > 
> > 
> > -- 
> > /* Lin Ke-Fong
> >  * anotherlin at gmail.com
> >  * I always do what I say, especially if it's something stupid.
> >  */
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