Thanks. richard@karlquist.com said: > 2. Magnetic state selection, as used in the 5071A, would be replaced by > optical pumping. Len Cutler was heartbroken that HP/Agilent management > wouldn't fund this effort. > It turns out that, even now in 2018, optical pumping is not ready for prime > time in a working standard because the lasers drift over time. Is there something fundamental in there, or is the lack of products because nobody has made the big investment required to figure out how to do it. What is the bandwidth of the laser? What happens if it drifts slightly? Can it be servoed? ... -- These are my opinions. I hate spam.

When I was working on fiber optic communication test, I remember hearing about lasers that were "tuned" with variable Peltier coolers. Power consumption is critical in a cesium standard that can run on batteries. Maybe the power consumption of the coolers is a deal breaker. Rick On 3/3/2018 6:18 PM, Hal Murray wrote: > Thanks. > > > richard@karlquist.com said: >> 2. Magnetic state selection, as used in the 5071A, would be replaced by >> optical pumping. Len Cutler was heartbroken that HP/Agilent management >> wouldn't fund this effort. > >> It turns out that, even now in 2018, optical pumping is not ready for prime >> time in a working standard because the lasers drift over time. > > Is there something fundamental in there, or is the lack of products because > nobody has made the big investment required to figure out how to do it. > > What is the bandwidth of the laser? What happens if it drifts slightly? Can > it be servoed? ... > > >

Am 04.03.2018 um 04:04 schrieb Richard (Rick) Karlquist: > When I was working on fiber optic communication test, > I remember hearing about lasers that were "tuned" with > variable Peltier coolers.  Power consumption is critical in > a cesium standard that can run on batteries.  Maybe > the power consumption of the coolers is a deal breaker. I have seen that stunt at SHF Design in Berlin, don't dare to calculate how long ago.. There were 2 lasers mixed with a 60 GHz beat frequency. Playing with one of the Peltiers moved that to 50 GHz. Easy to see the carrier creep on the spectrum analyzer. Cheers, Gerhard

Hi, On 03/04/2018 04:04 AM, Richard (Rick) Karlquist wrote: > When I was working on fiber optic communication test, > I remember hearing about lasers that were "tuned" with > variable Peltier coolers.  Power consumption is critical in > a cesium standard that can run on batteries.  Maybe > the power consumption of the coolers is a deal breaker. The peltier elements is needed and nowdays integrated with laserdiodes. For telecom lasers, which is fully integrated, wavelength shift with temperature and Peltier elements is needed to temperature-stabilize them when you run DWDM, which is the telecom scenario which is close, as the ITU-T channels is 100 GHz apart on a 199 THz base for the 1550 nm window. So, peltier elements is needed for sure. However, I wonder if there really is much power involved. Cheers, Magnus > Rick > > On 3/3/2018 6:18 PM, Hal Murray wrote: >> Thanks. >> >> >> richard@karlquist.com said: >>> 2.  Magnetic state selection, as used in the 5071A, would be replaced by >>> optical pumping.  Len Cutler was heartbroken that HP/Agilent management >>> wouldn't fund this effort. >> >>> It turns out that, even now in 2018, optical pumping is not ready for >>> prime >>> time in a working standard because the lasers drift over time. >> >> Is there something fundamental in there, or is the lack of products >> because >> nobody has made the big investment required to figure out how to do it. >> >> What is the bandwidth of the laser?  What happens if it drifts >> slightly?  Can >> it be servoed?  ... >> >> >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

 On 04 March 2018 at 21:21 Magnus Danielson <magnus@rubidium.dyndns.org> wrote:

 Hi,

 On 03/04/2018 04:04 AM, Richard (Rick) Karlquist wrote:

     When I was working on fiber optic communication test,
     I remember hearing about lasers that were "tuned" with
     variable Peltier coolers. Power consumption is critical in
     a cesium standard that can run on batteries. Maybe
     the power consumption of the coolers is a deal breaker.

 The peltier elements is needed and nowdays integrated with laserdiodes.
 For telecom lasers, which is fully integrated, wavelength shift with
 temperature and Peltier elements is needed to temperature-stabilize them
 when you run DWDM, which is the telecom scenario which is close, as the
 ITU-T channels is 100 GHz apart on a 199 THz base for the 1550 nm window.

 So, peltier elements is needed for sure.

 However, I wonder if there really is much power involved.

 Cheers,
 Magnus

     Rick

     On 3/3/2018 6:18 PM, Hal Murray wrote:

         Thanks.

         richard@karlquist.com said:

                1. Magnetic state selection, as used in the 5071A, would be replaced by

                   optical pumping. Len Cutler was heartbroken that HP/Agilent management
                   wouldn't fund this effort.

             It turns out that, even now in 2018, optical pumping is not ready for
             prime
             time in a working standard because the lasers drift over time.

         Is there something fundamental in there, or is the lack of products
         because
         nobody has made the big investment required to figure out how to do it.

         What is the bandwidth of the laser? What happens if it drifts
         slightly? Can
         it be servoed? ...

         _______________________________________________
         time-nuts mailing list -- time-nuts@febo.com
         To unsubscribe, go to
         https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
         and follow the instructions there.

         _______________________________________________
         time-nuts mailing list -- time-nuts@febo.com
         To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
         and follow the instructions there.

External cavity lasers with piezoelectric tuning (usually varies cavity length or tilts frequency selective grating) are usually used for such applications. Sacher laser do some compact units with integrated Peltier cooler etc: https://www.sacher-laser.com/home/industrial-lasers/point_and_line_laser_module/industrial_laser_modules/micron_laser.html To get pricing registration is required. They aren't cheap (a few thousand or so euros IIRC) but not too outrageous. Bruce > > On 04 March 2018 at 21:21 Magnus Danielson <magnus@rubidium.dyndns.org> wrote: > > Hi, > > On 03/04/2018 04:04 AM, Richard (Rick) Karlquist wrote: > > > > > > When I was working on fiber optic communication test, > > I remember hearing about lasers that were "tuned" with > > variable Peltier coolers. Power consumption is critical in > > a cesium standard that can run on batteries. Maybe > > the power consumption of the coolers is a deal breaker. > > > > > > The peltier elements is needed and nowdays integrated with laserdiodes. > For telecom lasers, which is fully integrated, wavelength shift with > temperature and Peltier elements is needed to temperature-stabilize them > when you run DWDM, which is the telecom scenario which is close, as the > ITU-T channels is 100 GHz apart on a 199 THz base for the 1550 nm window. > > So, peltier elements is needed for sure. > > However, I wonder if there really is much power involved. > > Cheers, > Magnus > > > > > > Rick > > > > On 3/3/2018 6:18 PM, Hal Murray wrote: > > > > > > > > > > Thanks. > > > > > > richard@karlquist.com said: > > > > > > > > > > 1. Magnetic state selection, as used in the 5071A, would be replaced by > > > > optical pumping. Len Cutler was heartbroken that HP/Agilent management > > > > wouldn't fund this effort. > > > > > > > > It turns out that, even now in 2018, optical pumping is not ready for > > > > prime > > > > time in a working standard because the lasers drift over time. > > > > > > > > > > > > > > Is there something fundamental in there, or is the lack of products > > > because > > > nobody has made the big investment required to figure out how to do it. > > > > > > What is the bandwidth of the laser? What happens if it drifts > > > slightly? Can > > > it be servoed? ... > > > > > > _______________________________________________ > > > time-nuts mailing list -- time-nuts@febo.com > > > To unsubscribe, go to > > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > and follow the instructions there. > > > > > > _______________________________________________ > > > time-nuts mailing list -- time-nuts@febo.com > > > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > and follow the instructions there. > > > > > > > > > > >

> > richard@karlquist.com said: > > 2. Magnetic state selection, as used in the 5071A, would be replaced by > > optical pumping. Len Cutler was heartbroken that HP/Agilent management > > wouldn't fund this effort. > > > It turns out that, even now in 2018, optical pumping is not ready for > prime > > time in a working standard because the lasers drift over time. > > Is there something fundamental in there, or is the lack of products because > nobody has made the big investment required to figure out how to do it. > FWIW, OSA has been giving at leat one talk per year on their optical Cs work, and as others have noted it's been coming "real soon" for a couple of years now. Here are some links: 2015 November: http://www.chronos.co.uk/files/pdfs/itsf/2015/day2/1410_High_performance_optically-pumped_cesium_beam_clock-PBerthoud-Oscilloquartz.pdf 2017 April: https://www.atis.org/wsts/library/2017/5-03_Oscilloquartz_Berthoud_Michaud_Optical%20Cs%20Beam%20clock%20for%20ePRTC%20applications_revision20170327.pdf

		Attila Kinali

On Sat, 3 Mar 2018 19:04:57 -0800 "Richard (Rick) Karlquist" <richard@karlquist.com> wrote: > On 3/3/2018 6:18 PM, Hal Murray wrote: > > Thanks. > > > > Is there something fundamental in there, or is the lack of products because > > nobody has made the big investment required to figure out how to do it. > > > > What is the bandwidth of the laser? What happens if it drifts slightly? Can Commercial laser diodes are available with line widths from 10MHz up to a few 100MHz. The problem with this is, that the center frequency varies with temperature and current. As ballpark figures you can use 10GHz per °C and mA. For laser pumping of atomic states, you need to stabilize the laser diode with additional feedback, a so called extended cavity diode laser (ECDL). Most commonly these days, a grating[1] or a distributed feedback (DFB, DFB external to the diode laser cavity is called "volume grating") is used. The grating can be thought of as a mirror with wavelength/frequency dependent reflection angle. A DFB is basically a wavelength selective filter. Both, grating and DFB are put in the laser path, such that they become part of the cavity, ie add another frequency selective element to the laser "oscillator". With this, one can get the linewidht down to 1kHz to 1MHz, mostly dependent on the strength of the feedback and on how much temperature and current fluctuations affect the center frequency. A good summary on how different factors add up in an ECDL can be found in [3]. The authors also presented a neat and cheap way how to build an ECDL in [4]. An alternative, a bit more complicated, but also more complete description can be found in [5]. Under the assumption you have selected the right diode and designed the feedback system well, you can get system that will be first order indepented of the laser diodes behaviour. I.e. the external cavity will be the main wavelength determining element. The problems for long term use in commercial standards seem to be the second order effects. Mainly the position of mode jumps (sudden, large jumps of frequency when applying only a small change of tuning to the system). While it is easy to tune the ECDL such, that these mode jumps do not happen withing the region of interest, it is not so easy to ensure that aging does not bring one of these mode jumps right to the point where one would like to keep the laser. Detecting of these mode jumps is also not easy, the straight forward way requires a second laser to measure the difference frequency. A second way of using the amplitude varation during mode jumps seems not to be as reliable. But! For 1.5µm communication laser systems, all these problems have been solved and we have very reliable lasers that stay on frequency with a very high stability (modern laser communication systems use a channel spacing as low as 1GHz @ 1.5µm). So there is hope that these techniques will spill over to wavelength ranges more interesting to atomic standards. Most likekly the first one would be 850nm (close to the Ceasium D2 line), which is being used for short range, cheap optical networks. > When I was working on fiber optic communication test, > I remember hearing about lasers that were "tuned" with > variable Peltier coolers. Power consumption is critical in > a cesium standard that can run on batteries. Maybe > the power consumption of the coolers is a deal breaker. If all you have is just a laser diode with at most DFB, but no external cavity (as is usualy with communication lasers), then the only two ways to tune are temperature and current. But current will also modulate intensitiy, so people tend to try to keep current more or less constant, while doing the tuning with temperature. For a system with external cavity, it's enough to keep current and temperature stable, which makes the power consumption less pronounced. The gotcha here is, that one might need to tune temperature a bit to move a mode jump out of the way. But even if you dont have an ECDL, it's only a laser you have to cool, which is a very low mass, and the cooling power needed is just what you pump into it (usually a 5mW laser is enough for atomic spectroscopy, which translates to <100mW electrical power needed). On Sun, 4 Mar 2018 21:41:15 +1300 (NZDT) Bruce Griffiths <bruce.griffiths@xtra.co.nz> wrote: > External cavity lasers with piezoelectric tuning (usually varies cavity length or tilts frequency selective grating) are usually used for such applications. > > Sacher laser do some compact units with integrated Peltier cooler etc: > > https://www.sacher-laser.com/home/industrial-lasers/point_and_line_laser_module/industrial_laser_modules/micron_laser.html > > To get pricing registration is required. The Sacher module is a neat little device, that integrates all of the components needed into a tiny little package. More information on its construction and performance can be found in [6] (note: their calculation of linewidth is wrong, it should be 36kHz/sqrt(2) = 25kHz). The price was, when I looked at it 2 years ago, at 2500€. Attila Kinali [1] https://en.wikipedia.org/wiki/Diffraction_grating [2] https://www.youtube.com/watch?v=EuWI1WPrZ2I [3] "Mode stability of external cavity diode lasers", by Saliba, Junker, Turner, Scholten, 2009 http://dx.doi.org/10.1364/AO.48.006692 https://cpb-ap-southeast-2-juc1ugur1qwqqqo4.stackpathdns.com/blogs.unimelb.edu.au/dist/5/118/files/2015/11/Saliba-et-al.-2009-Applied-Optics-Mode-stability-of-external-cavity-diode-lasers-1buob6t.pdf [4] "Littrow configuration tunable external cavity diode laser with fixed direction output", by Hawthorn, Weber, Scholten, 2001 https://doi.org/10.1063/1.1419217 https://www.thevespiary.org/library/Files_Uploaded_by_Users/no1uno/pdf/Instrumentation/Laser.Design/Hawthorn.Weber.Scholten.Littrow.Configuration.Tuneable.External.Cavity.Diode.Laser.with.Fixed.Direction.Output.Beam.pdf [5] "A narrow-band tunable diode laser system with grating feedback, and a saturated absorption spectrometer for Cs and Rb", by MacAdam, Steinbach, Wieman, 1992 https://doi.org/10.1119/1.16955 https://www.thevespiary.org/library/Files_Uploaded_by_Users/no1uno/pdf/Instrumentation/Laser.Design/Laser.Locking/MacAdam.Steinchach.Wieman.A.Narrow.Band.Tunable.Diode.Laser.System.with.Grating.Feedback.and.a.Saturated.Absorption.Spectrometer.for.Cs.and.Rb.pdf [6] "Compact Bragg Grating Stabilised Ridge Waveguide Laser Module with a power of 380mW at 780nm", by Rauch and Sacher, 2015 https://doi.org/10.1109/LPT.2015.2438545 https://www.sacher-laser.com/downloads/publications/5r1249_en.pdf -- <JaberWorky> The bad part of Zurich is where the degenerates throw DARK chocolate at you.