Discussion:
=?utf-8?q?=3F=3D=3D=3Futf-8=3Fq=3F__a_newbie_question?= =?utf-8?q?=3A_where_can_I_purchase_794=2E7_nm_VCSEL_for_building_CPT_rubi?= =?utf-8?q?dium_clock=3F?=
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Henk Peek
2018-06-07 19:18:59 UTC
Permalink
Rb vapor-cell clock demonstration with a frequency-doubled telecom laser

Applied Optics Vol. 57, Issue 16, pp. 4707-4713 (2018) •https://doi.org/10.1364/AO.57.004707

Abstract

We employ a recently developed laser system, based on a low-noise telecom laser emitting around 1.56 μm, to evaluate its impact on the performance of an Rb vapor-cell clock in a continuous-wave double-resonance scheme. The achieved short-term clock instability below 2.5·10−13·𝜏−1/2 demonstrates, for the first time, the suitability of a frequency-doubled telecom laser for this specific application. We measure and study quantitatively the impact of laser amplitude and frequency noises and of the ac Stark shift, which limit the clock frequency stability on short timescales. We also report on the detailed noise budgets and demonstrate experimentally that, under certain conditions, the short-term stability of the clock operated with the low-noise telecom laser is improved by a factor of three compared to clock operation using the direct 780-nm laser.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Henk Peek
On Mon, 4 Jun 2018 21:31:56 +0800
I'm planning to build a CPT (coherent-population-trapping) rubidium clock
as my next hobby project. The main purpose is to learn the principles
behind CPT rubidium clock, and hopefully got similar or better performance
than commercial miniature rubidium clock such as FE-5680A.
Building a CPT clock is slightly more involved than you might think
at first. The laser diode is only one part of it. You will most likely
be able to improve on the short-term stability of the FE-5680 (which
is rather poor). But I doubt you will be able to improve much on
the long term stability, which is where things actually become interesting,
if you use a naive approach.
Nevertheless, I have not seen many 794/795nm diodes around. The only
one that I have the datasheet of is the one from Vixar.
You might want want to consider going for the D2 line instead of the
D1 line, as 780nm diodes are more commonly available than 795nm. You will
also need to buy several of those and select the ones that come closest
to the wavelength at the desired opearating conditions (usuall spread
is +/-1nm to +/-10nm). Do not assume you can tune more than 0.1nm with
temperature and current (rule of thumb is that you get about 10GHz
per °C and mA). If you need more tuning range, you will need to add an
external cavity (can give you up to 5nm range), which then needs to be
tuned to the 3.45GHz (ie it's length needs to be approximately 8-9cm).
Alternatively, you can get two S1-0780-XXX from Sacher Laser
(cost IIRC 2500€ each) and keep them 6.9GHz apart (using an optical PLL).
If you have enough money to spend, I'd go for two Cateye diode laser CEL's
from Moglabs (cost AFAIK 5000€ each)
No matter what you choose, you will need some wavelength stabilization
scheme. You can either do that with the vapor cell itself or use
an additional cell and do a DVALL or a saturated absorption locking.
Note that this addtional cell will need to be without buffer gas.
An external cell will offer better stability and thus lower noise,
which directly translates into higher stability.
As polarisation scheme, I suggest using σ+/σ- as it seems to be more
robust than the lin/lin schemes.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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Magnus Danielson
2018-06-11 04:53:49 UTC
Permalink
One might then ask what the availability and pricetag is for nonlinear
chrystal needed for frequency doubling.

If it is esoteric enough to get and priced similar, well then the gain
is lost.

Cheers,
Magnus
Post by Henk Peek
Rb vapor-cell clock demonstration with a frequency-doubled telecom laser
Applied Optics Vol. 57, Issue 16, pp. 4707-4713 (2018) •https://doi.org/10.1364/AO.57.004707
Abstract
We employ a recently developed laser system, based on a low-noise telecom laser emitting around 1.56 μm, to evaluate its impact on the performance of an Rb vapor-cell clock in a continuous-wave double-resonance scheme. The achieved short-term clock instability below 2.5·10−13·𝜏−1/2 demonstrates, for the first time, the suitability of a frequency-doubled telecom laser for this specific application. We measure and study quantitatively the impact of laser amplitude and frequency noises and of the ac Stark shift, which limit the clock frequency stability on short timescales. We also report on the detailed noise budgets and demonstrate experimentally that, under certain conditions, the short-term stability of the clock operated with the low-noise telecom laser is improved by a factor of three compared to clock operation using the direct 780-nm laser.
© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Henk Peek
On Mon, 4 Jun 2018 21:31:56 +0800
I'm planning to build a CPT (coherent-population-trapping) rubidium clock
as my next hobby project. The main purpose is to learn the principles
behind CPT rubidium clock, and hopefully got similar or better performance
than commercial miniature rubidium clock such as FE-5680A.
Building a CPT clock is slightly more involved than you might think
at first. The laser diode is only one part of it. You will most likely
be able to improve on the short-term stability of the FE-5680 (which
is rather poor). But I doubt you will be able to improve much on
the long term stability, which is where things actually become interesting,
if you use a naive approach.
Nevertheless, I have not seen many 794/795nm diodes around. The only
one that I have the datasheet of is the one from Vixar.
You might want want to consider going for the D2 line instead of the
D1 line, as 780nm diodes are more commonly available than 795nm. You will
also need to buy several of those and select the ones that come closest
to the wavelength at the desired opearating conditions (usuall spread
is +/-1nm to +/-10nm). Do not assume you can tune more than 0.1nm with
temperature and current (rule of thumb is that you get about 10GHz
per °C and mA). If you need more tuning range, you will need to add an
external cavity (can give you up to 5nm range), which then needs to be
tuned to the 3.45GHz (ie it's length needs to be approximately 8-9cm).
Alternatively, you can get two S1-0780-XXX from Sacher Laser
(cost IIRC 2500€ each) and keep them 6.9GHz apart (using an optical PLL).
If you have enough money to spend, I'd go for two Cateye diode laser CEL's
from Moglabs (cost AFAIK 5000€ each)
No matter what you choose, you will need some wavelength stabilization
scheme. You can either do that with the vapor cell itself or use
an additional cell and do a DVALL or a saturated absorption locking.
Note that this addtional cell will need to be without buffer gas.
An external cell will offer better stability and thus lower noise,
which directly translates into higher stability.
As polarisation scheme, I suggest using σ+/σ- as it seems to be more
robust than the lin/lin schemes.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-***@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Attila Kinali
2018-06-11 07:26:35 UTC
Permalink
On Mon, 11 Jun 2018 06:53:49 +0200
Post by Magnus Danielson
One might then ask what the availability and pricetag is for nonlinear
chrystal needed for frequency doubling.
It cannot be too much, given the fact that these are used in
green laser pointers.

Though, I have to say I am astonished how expensive those VCSEL are.
I would have guessed they are below $100/pcs, given that "normal"
laser diodes are usually in the order of $10-$20.


Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
_______________________________________________
time-nuts mailing list -- time-***@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Bruce Griffiths
2018-06-11 07:49:07 UTC
Permalink
The output wavelength of a VCSEL is current and temperature dependent so using a low noise current source and regulating the chip temperature is usually necessary to allow locking to an atomic transition.
Most VCSELS for such applications include a peltier module within the housing.

Bruce
Post by Attila Kinali
On Mon, 11 Jun 2018 06:53:49 +0200
Post by Magnus Danielson
One might then ask what the availability and pricetag is for nonlinear
chrystal needed for frequency doubling.
It cannot be too much, given the fact that these are used in
green laser pointers.
Though, I have to say I am astonished how expensive those VCSEL are.
I would have guessed they are below $100/pcs, given that "normal"
laser diodes are usually in the order of $10-$20.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-***@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

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