Re: [time-nuts] Current state of optical clocks and the definition of the second
Hi, I've took the time to read carefully your long and detailed message Magnus and this was very interesting. I've learned many things that have enabled me to investigate further. Ah yes, you're right saying that the more you fall into these things, the more you discover that you have to learn. Recently I've worked a lot on PLLs and I've actually learned a lot on special care to ensure low noise Very interesting. By the way I'm still working on this topic to improve again the noise (currently on a 3 GHz LO) Here are some experiment results : http://www.ptp-images.com/affiche-directement-l-image-kccsz71c9a.html 1. Setup #1 (blue plot) HP5370A standard input from HP GPSDO EXT input not connected, internal Arming 0.4s rate START input from 10 MHz distribution unit RacalDana 9478 Rubidium 2. Setup #2 (pink plot) HP5370A standard input from HP GPSDO EXT input not connected, internal Arming 0.4s rate START input from DUT (10 MHz homemade GPSDO) I'm not sure this is the proper way to connect everything... but this is the setup providing the lowest ADEV... which is between 1E-10 and 1E-13. But is the truth ? I feel strange the two plots having the same decreasing path along a linear slope (I mean linear on the log-log plot) ... I'm not sure of what I'm measuring ? Could this be the system measurement floor ? By the way how to measure the ADEV floor of a system other than having a source greater than the measurement system ? What could be these oscillations on the homemade (not by me) GPSDO ? I've tried to downmix the DUT 10 MHz to few kHz using a SR DDS generator and a double balanced mixer from minicircuit via a low pass filter tuned at 100 kHz, but the level wasn't high enough for the counter (which I found strange as it was already nearly 200mV). I hadn't anything in hands to make a squarer quickly so I've just added a Minicircuits RF amplifier. The level was good but the ADEV has jumped to 1E-6. The signal was noisy already on the oscilloscope which I know is for sure the cause. I need to make a squarer. I was hesitating between several methods : using a CMOS gate, but this will increase the flicker noise from what I've read, using an amplifier and clamping diodes or a fast comparator which might create some noise around the trigger point... Any recommendation there ? I'll try to make this squarer next week to continue my investigations Cheers Stephane -Message d'origine- De : time-nuts [mailto:time-nuts-boun...@febo.com] De la part de Magnus Danielson Envoyé : mercredi 14 janvier 2015 06:05 À : time-nuts@febo.com Cc : mag...@rubidium.se Objet : Re: [time-nuts] Current state of optical clocks and the definition of the second On 01/13/2015 11:41 AM, Attila Kinali wrote: > On Mon, 12 Jan 2015 20:09:45 + > Gregory Maxwell < <mailto:gmaxw...@gmail.com> gmaxw...@gmail.com> wrote: > >> On Mon, Jan 12, 2015 at 12:34 PM, Attila Kinali < <mailto:att...@kinali.ch> >> att...@kinali.ch> wrote: >> Seems that the state of the art in stabilized lasers has improved a >> lot lately, e.g. there are commercial available 1550nm devices which >> have a <=3Hz line-width: <http://stablelasers.com/products.html> >> http://stablelasers.com/products.html (well >> on a short term basis, the medium term performance is not so >> impressive) > > Laser stabilization, especially for quantum metrology is still an > actively researched field. Current state of the art is IIRC 0.3Hz > linewidth (sorry, cannot find the reference at the moment). > Mid- and long term stability depends highly on the reference used. > Current research is fucused mainly on special, low vibration > structures made out of low expansion glass or silicon. And these > cavities are usually put into a temperature controlled chamber in > vacuum. Well, guess what I found standing around in a lab with an optical comb? :) With optical line-widths in sub-Hz range and optical combs you have a nice way of comparing the frequency of that free-running and un-steerable but stable oscillator. However, as you mix it down the noise of the optical comb will dominate, but you can know which multiple of the optical comb and offset it is. >> Considering the rarity and extreme cost of H-masers, or just really >> exceptional quarts oscillators; might it be the case that optical LOs >> start looking interesting for applications which just need stability >> (or being steered by other sources; e.g. GPSDL)? > > Well, an 8607 costs more than a Rb-standard. Yes, the 8607 has lower > close in phase noise and up to several 1000s it rivals the Rb, but > handling it is much more difficult
Re: [time-nuts] Current state of optical clocks and the definition of the second
Bob - What I am saying is, even at the levels you mentioned, what is measured is I believe the combination of phase and AM. In other words, you are just measuring noise, but, are not certain if it is all phase, or phase plus some AM. At least that is my recollection when I was heavily involved in it some 30 years ago. Thanks - Mike Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 office 908-902-3831 cell -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Thursday, January 15, 2015 7:48 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Current state of optical clocks and the definition of the second Hi I guess the question becomes how low is low. If it’s a 50 ohm system If the power level is rational If you are at room temperature There are some limits on how low low can be. You have a -174 dbm / Hz thermal floor. AM or PM noise can only be 3db better than the thermal floor. At a power level of 1 watt, that’s a -204 dbc / Hz limit. You will spend some time correlating to that level. You also may need to play a bit with the input circuits to handle the 1W without damage. At a somewhat more common 100 mw, the limit is -194. People have been measuring phase noise in the > -190 dbc / Hz range for at least 20 years now. Correlation may take a week at some offsets. Time will be longer or shorter at other offsets. As with anything else, the more money (correlation channels) you throw at the problem, the quicker it will go. Numbers in the -180 vicinity with normal gear, offsets, and FFT windows are an overnight run sort of thing. Bob ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
Hi I guess the question becomes how low is low. If it’s a 50 ohm system If the power level is rational If you are at room temperature There are some limits on how low low can be. You have a -174 dbm / Hz thermal floor. AM or PM noise can only be 3db better than the thermal floor. At a power level of 1 watt, that’s a -204 dbc / Hz limit. You will spend some time correlating to that level. You also may need to play a bit with the input circuits to handle the 1W without damage. At a somewhat more common 100 mw, the limit is -194. People have been measuring phase noise in the > -190 dbc / Hz range for at least 20 years now. Correlation may take a week at some offsets. Time will be longer or shorter at other offsets. As with anything else, the more money (correlation channels) you throw at the problem, the quicker it will go. Numbers in the -180 vicinity with normal gear, offsets, and FFT windows are an overnight run sort of thing. Bob > On Jan 14, 2015, at 9:47 PM, Mike Feher wrote: > > Hi - > > I agree with what you stated, however, I am not sure that at real low levels > they are actually discernible. Regards - Mike > > Mike B. Feher, EOZ Inc. > 89 Arnold Blvd. > Howell, NJ, 07731 > 732-886-5960 office > 908-902-3831 cell > > -Original Message- > From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp > Sent: Wednesday, January 14, 2015 6:14 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Current state of optical clocks and the definition > of the second > > Hi > > More or less by definition: > > AM noise has the sidebands in phase, PM noise has the sidebands out of phase. > PM adds to no envelope power, AM adds to the envelope power. If you have > purely random noise, half of the power is AM, half is PM by this approach. If > you have what is effectively a SDR (high speed ADC(s), decimators, cross > correlation …) doing your phase noise measurement, figuring out sidebands and > phase is part of the process. With an old style single mixer approach, you > switch your operating point on the mixer. > > Bob > > > ___ > 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
I have a page that illustrates how you can use a delay line and a mixer to separately obtain AM and PM http://www.ko4bb.com/Timing/Phase_Detector Didier KO4BB On January 14, 2015 1:19:11 PM CST, Mike Feher wrote: >At those low levels, how does one differentiate between phase or AM >noise? Thanks & Regards - Mike > >Mike B. Feher, EOZ Inc. >89 Arnold Blvd. >Howell, NJ, 07731 >732-886-5960 office >908-902-3831 cell > >-Original Message- >From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce >Griffiths >Sent: Wednesday, January 14, 2015 1:22 AM >To: Discussion of precise time and frequency measurement >Subject: Re: [time-nuts] Current state of optical clocks and the >definition of the second > >Although the phase noise when using optical combs to generate Rf >signals is low there is no mention of the am noise. > >Bruce > >___ >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. -- Sent from my Motorola Droid Razr HD 4G LTE wireless tracker while I do other things. ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
Hi - I agree with what you stated, however, I am not sure that at real low levels they are actually discernible. Regards - Mike Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 office 908-902-3831 cell -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Wednesday, January 14, 2015 6:14 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Current state of optical clocks and the definition of the second Hi More or less by definition: AM noise has the sidebands in phase, PM noise has the sidebands out of phase. PM adds to no envelope power, AM adds to the envelope power. If you have purely random noise, half of the power is AM, half is PM by this approach. If you have what is effectively a SDR (high speed ADC(s), decimators, cross correlation …) doing your phase noise measurement, figuring out sidebands and phase is part of the process. With an old style single mixer approach, you switch your operating point on the mixer. Bob ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
Hi More or less by definition: AM noise has the sidebands in phase, PM noise has the sidebands out of phase. PM adds to no envelope power, AM adds to the envelope power. If you have purely random noise, half of the power is AM, half is PM by this approach. If you have what is effectively a SDR (high speed ADC(s), decimators, cross correlation …) doing your phase noise measurement, figuring out sidebands and phase is part of the process. With an old style single mixer approach, you switch your operating point on the mixer. Bob > On Jan 14, 2015, at 2:19 PM, Mike Feher wrote: > > At those low levels, how does one differentiate between phase or AM noise? > Thanks & Regards - Mike > > Mike B. Feher, EOZ Inc. > 89 Arnold Blvd. > Howell, NJ, 07731 > 732-886-5960 office > 908-902-3831 cell > > -Original Message- > From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce > Griffiths > Sent: Wednesday, January 14, 2015 1:22 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Current state of optical clocks and the definition > of the second > > Although the phase noise when using optical combs to generate Rf signals is > low there is no mention of the am noise. > > Bruce > > ___ > 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
At those low levels, how does one differentiate between phase or AM noise? Thanks & Regards - Mike Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 office 908-902-3831 cell -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths Sent: Wednesday, January 14, 2015 1:22 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Current state of optical clocks and the definition of the second Although the phase noise when using optical combs to generate Rf signals is low there is no mention of the am noise. Bruce ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
Interestingly they use regenerative dividers. Pretty good read. Thanks Paul WB8TSL On Tue, Jan 13, 2015 at 4:49 PM, Tom Knox wrote: > I think the key to this concept is an optical comb filter. > Archita Hati of the Phase Noise measurement Group at NIST has been > researching ultra low phase noise 5MHz references using an optical > standard and comb filter > as well as extensive RF components to down converting to the desired > frequency. > In experiments I believe she has achieved phase noise better then -154db @ > 1Hz offset. > It does appear to be the future but currently is far to large and complex > for most if any > practical use. I believe this link is the paper by Archita Hati I referred > addressing > State-of-the-Art RF Signal Generation From Optical Frequency Division. > http://tf.boulder.nist.gov/general/pdf/2646.pdf > Enjoy; > Thomas Knox > > Thomas Knox > > > > > From: namic...@gmail.com > > Date: Wed, 14 Jan 2015 07:00:09 +1100 > > To: time-nuts@febo.com > > CC: namic...@gmail.com > > Subject: Re: [time-nuts] Current state of optical clocks and the > definition of the second > > > > > > THe stability /accuracy of lasers is entirely dependent on the cavity > length. > > Materials used are usually invar or silica, so you are no better off than > > with a quartz crystals. > > They are just a resonant cavity. > > cheers, > > Neville Michie > > ___ > > 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. > ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
Dr David Kirkby Managing Director Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3 6DT, United Kingdom Registered in England and Wales as company number 08914892 http://www.kirkbymicrowave.co.uk/ Tel 07910 441670 / +44 7910 441670 (0900-2100 GMT) On 13 Jan 2015 20:39, "Neville Michie" wrote: > THe stability /accuracy of lasers is entirely dependent on the cavity length. > Materials used are usually invar or silica, so you are no better off than > with a quartz crystals. > They are just a resonant cavity. > cheers, > Neville Michie I do realise that thermal stability is important. The pulsed titanium sapphire laser I used during my PhD took about 8 hours to become stable, and that had a lump of invar in it which was probably about 1.2 m long and 120 mm in diameter. But to say that the stability/accuracy depends entirely on the cavity length is a gross simplification. Someone posted a link to some information on getting narrow linewidths from cheap semiconductor lasers with something as simple as a piece of glass in front. That does nothing to stabilise the cavity length. There's a free webiminar on the 29th Jan at 1300 PST with the title "Laser Test of RIN, Linewidth and Optical Noise Parameters". http://www.microwavejournal.com/events/1310-laser-test-of-rin-linewidth-and-optical-noise-parameters Dave. ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
Although the phase noise when using optical combs to generate Rf signals is low there is no mention of the am noise. Bruce On Tuesday, January 13, 2015 02:49:33 PM Tom Knox wrote: > I think the key to this concept is an optical comb filter. > Archita Hati of the Phase Noise measurement Group at NIST has been > researching ultra low phase noise 5MHz references using an optical standard > and comb filter as well as extensive RF components to down converting to > the desired frequency. In experiments I believe she has achieved phase > noise better then -154db @ 1Hz offset. It does appear to be the future but > currently is far to large and complex for most if any practical use. I > believe this link is the paper by Archita Hati I referred addressing > State-of-the-Art RF Signal Generation From Optical Frequency Division. > http://tf.boulder.nist.gov/general/pdf/2646.pdf > Enjoy; > Thomas Knox > > Thomas Knox > > > From: namic...@gmail.com > > Date: Wed, 14 Jan 2015 07:00:09 +1100 > > To: time-nuts@febo.com > > CC: namic...@gmail.com > > Subject: Re: [time-nuts] Current state of optical clocks and the > > definition of the second > > > > > > THe stability /accuracy of lasers is entirely dependent on the cavity > > length. Materials used are usually invar or silica, so you are no better > > off than with a quartz crystals. > > They are just a resonant cavity. > > cheers, > > Neville Michie > > ___ > > 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. ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On 01/13/2015 11:41 AM, Attila Kinali wrote: On Mon, 12 Jan 2015 20:09:45 + Gregory Maxwell wrote: On Mon, Jan 12, 2015 at 12:34 PM, Attila Kinali wrote: Seems that the state of the art in stabilized lasers has improved a lot lately, e.g. there are commercial available 1550nm devices which have a <=3Hz line-width: http://stablelasers.com/products.html (well on a short term basis, the medium term performance is not so impressive) Laser stabilization, especially for quantum metrology is still an actively researched field. Current state of the art is IIRC 0.3Hz linewidth (sorry, cannot find the reference at the moment). Mid- and long term stability depends highly on the reference used. Current research is fucused mainly on special, low vibration structures made out of low expansion glass or silicon. And these cavities are usually put into a temperature controlled chamber in vacuum. Well, guess what I found standing around in a lab with an optical comb? :) With optical line-widths in sub-Hz range and optical combs you have a nice way of comparing the frequency of that free-running and un-steerable but stable oscillator. However, as you mix it down the noise of the optical comb will dominate, but you can know which multiple of the optical comb and offset it is. Considering the rarity and extreme cost of H-masers, or just really exceptional quarts oscillators; might it be the case that optical LOs start looking interesting for applications which just need stability (or being steered by other sources; e.g. GPSDL)? Well, an 8607 costs more than a Rb-standard. Yes, the 8607 has lower close in phase noise and up to several 1000s it rivals the Rb, but handling it is much more difficult than handling an Rb. Also, if you want to buy one of those exceptionally low noise/high stable 8607's (those that go down into the 10^-14 range) you'd have to sell your car. But, if you buy a H-maser from SpectraTime, you get a 8607 for free ;-) That is also the only way to get the 8607 now, as Oscilloquartz is closing down that business. There used to be quite some literature on how to build low noise quartz oscillators. Most of those books are out of print today. With two notable exceptions: "Discrete Oscillator Design: Linear, Nonlinear, Transient, and Noise Domains" by Randall Rhea, 2010 and "Understanding Quartz Crystals and Oscillators", by Ramon Cerda, 2014 I had a look at the book by Rhea, it looks quite well written and contains a lot of real world information, but is a bit weak on the more theoretical part (description of oscillation, noise sources,...) and thus on the on the why things are done that way. I didn't had the chance to buy Cerdas book yet. An interesting book in that context is Enrico Rubiolas book on phase-noise, which among other things goes into explain the Leeson model of oscillators and it's real life design aspects. The UFFC has some of the older books online. You need to be registered to access them, though. There is also a lot of knowledge on quartz crystalls hidden in old papers, but going trough them is some serious work. On the topic of opto-electronic oscillators, those are technologically nice, but they are rather bulky. That's why they are mostly used in research projects for atomic clocks. Also getting them to do low phase noise is not that easy, and unlike quartz oscillators, there is not much literature about that. It's a serious bulk of glas in there, but the laser-technology as well as temperature-stabilization of it isn't rocket science, (They can be down-converted to microwave frequencies using an optical comb; a mode-locked laser whos pulses are phase locked to an incoming beam.) That is actually the current trend. There was a paper by NIST last year on downconverting the beat frequency of an optical comb down to RF using a frequency divider chain. They managed to get noise measures that rival that of a good quartz oscillator at 5MHz. Ie at higher frequencies, it is actually better than what a quartz oscillator can deliver. (for some reason i have not archived that paper and google fails me) The NIST T&F archive is where you should go. Nice folks doing that work. Certainly just the local oscillator is _closer_ to something a time-nut might experiment with than a complete optical atomic standard (if still not quite in reach). Well, building a CPT based Rb vapor cell frequency standard should be feasible. Yes, it's not a primary standard, but should do the job for most :-) From what i've read, using one of the MOT cells like those of Sachser Laser [1] one might even be able to build a primary standard. But my understanding of MOT is relatively weak and i cannot say how difficult it actually would be. But it would be definitly a fun project to try :-) Building a MOT setup is relatively easy know, I have not yet seen it go sub 100.000 USD, but it seems like modern setups could do that if you let it. I've been playing with such a s
Re: [time-nuts] Current state of optical clocks and the definition of the second
I think the key to this concept is an optical comb filter. Archita Hati of the Phase Noise measurement Group at NIST has been researching ultra low phase noise 5MHz references using an optical standard and comb filter as well as extensive RF components to down converting to the desired frequency. In experiments I believe she has achieved phase noise better then -154db @ 1Hz offset. It does appear to be the future but currently is far to large and complex for most if any practical use. I believe this link is the paper by Archita Hati I referred addressing State-of-the-Art RF Signal Generation From Optical Frequency Division. http://tf.boulder.nist.gov/general/pdf/2646.pdf Enjoy; Thomas Knox Thomas Knox > From: namic...@gmail.com > Date: Wed, 14 Jan 2015 07:00:09 +1100 > To: time-nuts@febo.com > CC: namic...@gmail.com > Subject: Re: [time-nuts] Current state of optical clocks and the definition > of the second > > > THe stability /accuracy of lasers is entirely dependent on the cavity length. > Materials used are usually invar or silica, so you are no better off than > with a quartz crystals. > They are just a resonant cavity. > cheers, > Neville Michie > ___ > 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
THe stability /accuracy of lasers is entirely dependent on the cavity length. Materials used are usually invar or silica, so you are no better off than with a quartz crystals. They are just a resonant cavity. cheers, Neville Michie ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Tue, 13 Jan 2015 17:46:01 + "Dr. David Kirkby (Kirkby Microwave Ltd)" wrote: > I had a brief read. Equation 1 made me wonder what could be achieved > with a cheap HeNe laser. It should be fairly easy to mix a couple of > HeNe lasers on a photodiode and look at the difference frequency > between them, so gaining insight into their stability. A quick check > on Wikipedia > > https://en.wikipedia.org/wiki/Helium%E2%80%93neon_laser > > indicates a spectral width of 0.002 nm. > > The common 632.8 nm laser has a frequency of 4.7 x 10^14 Hz, or 470 THz. Oops.. i just reread the part of the paper an realized that i answered in a completely meaningless way. Sorry about that. For the real answer: You can use a HeNe laser to provide with a stable wavelength, but as with all lasers, the linewidth and stability are determined by the cavity, not by the atomic transition. The width of the atomic transition is much wider than the cavity free spectral range. Usually, these lasers have a 2-10cm long cavity, which results in a free spectral range of 60GHz to 3Ghz. The exact wavelength depends on the length of the cavity. Which means that any temperature change will shift the laser wavelength around. And we are not yet talking about possible mode hops. All this together will lead to laser wavelengths of different HeNe laser tubes that are so far apart that a simple diode detection of the beat frequency will not work (the beat frequency could be in the several 10GHz and/or wander around very quickly). When stable lasers are needed, they are locked to something that does not change. For example a vapor cell (DAVLL) or to a high stability fabry-perot cavity (Pound-Drever-Hall). Both, the vapor cell or the cavity are temperature stabilized. Locked also means that the laser is steered, ie the wavelength of the laser is controlled electronically using the feedback of the reference element. Long story short, a simple HeNe laser will not give you anything stable, without some additional stabilization. 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-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Tue, 13 Jan 2015 19:37:05 +0100 Attila Kinali wrote: > If you use a standard laser diode, these have a linewidth of > around 20-100MHz. If you provide them the slightest feedback, > they go down to 1MHz easily (ie just by adding some window glass > infront of the laser, that reflects a tiny bit back). > Using a more sophisticated scheme with a grating and you get into > the range of 1-100kHz, which is pretty darn good, and enough for > vapor cells with their broad lines. Wieman wrote a couple of papers > on how to build such laser system [1-3]. Also worth a look are the two > papers by Libbrecht [4,5]. For those who need some theory for > calculation or as background [6] will be a good start. It also > contains a lot of usefull references. Oh.. i forgot to mention. The DIY holographcy community is full of people who build their own narrow linewidth, stabilized lasers. They have also quite a few, hands-on descriptions on how to build grating based external cavity diode lasers. Especially W's website[1] and blog[2]. Attila Kinali [1] http://redlum.xohp.pagesperso-orange.fr/argonlaser.html [2] https://hololaser.wordpress.com/ -- 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-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Tue, Jan 13, 2015 at 5:46 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: > I had a brief read. Equation 1 made me wonder what could be achieved > with a cheap HeNe laser. It should be fairly easy to mix a couple of See Sams Laser Faq section on stabalized HeNe Lasers: http://www.repairfaq.org/sam/laserchn.htm#chnsshnl1 This uses zeeman splitting to get two different polarization modes lasing at slightly different wavelengths. (this is described in more detail elsewhere in the FAQ about some commercial lasers that use this effect.) There are do it yourself at home grade (/ easily available surplus parts) things you can do to get the short term linewidth down to about 4MHz or so, sadly 4MHz out of 470THz is only 1e-8 or so, so not super competitive with some off the shelf OCXO. You're also then stuck with an optical standard, and the down conversion to microwave is decidedly more complex. It would probably be a fun time-nuts project, even given the not amazing performance, if not for the difficulty in down-converting to something that could feed a counter. ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Tue, 13 Jan 2015 17:46:01 + "Dr. David Kirkby (Kirkby Microwave Ltd)" wrote: > Of course I'm not suggesting a HeNe would provide the stability of > cutting edge research laser optical clock, but they are easily within > the budget of a hobbyist and could be a bit of fun to try to measure > their stability/phase noise. The tricky bit would be getting 470 THz > down to 10 MHz, but a cheap and quick experiment would prove whether > it is a total waste of time or not. Actually, you can get better than that, and cheaper. If you use a standard laser diode, these have a linewidth of around 20-100MHz. If you provide them the slightest feedback, they go down to 1MHz easily (ie just by adding some window glass infront of the laser, that reflects a tiny bit back). Using a more sophisticated scheme with a grating and you get into the range of 1-100kHz, which is pretty darn good, and enough for vapor cells with their broad lines. Wieman wrote a couple of papers on how to build such laser system [1-3]. Also worth a look are the two papers by Libbrecht [4,5]. For those who need some theory for calculation or as background [6] will be a good start. It also contains a lot of usefull references. That said. For just doing something like CPT, you don't need to narrow the linewidth of a standard laser diode. Eg the CSAC uses just a standard VCSEL without any additional optics. The disadvantage is, that your only means to control the laser wavelength is temperature and current. Also, you will see mode jumps within the range you are interested in. Attila Kinali [1] "Using diode lasers for atomic physics", by Wieman, Holberg, 1990 http://web.mit.edu/kimt/www/nice_readings/wieman-diode-lasers.pdf [2] "A narrow-band tunable diode laser system with grating feedback, and a saturated absorption spectrometer for Cs and Rb", by MacAdam, Steinbach, Wieman, 1992 http://fisica.usach.cl/~iolivare/MacAdamSteinbachWieman92.pdf [3] "Inexpensive laser cooling and trapping experiment for undergraduate laboratories", by Wieman, Flowers, Gilbert, 1994 http://ajp.aapt.org/resource/1/ajpias/v63/i4/p317_s1 [4] "Teaching physics with 670nm diode lasers - construction of stabilized lasers and lithium cells", by Libbrecht, et al, 1995 http://ajp.aapt.org/resource/1/ajpias/v63/i8/p729_s1 [5] "Teaching physics with 670nm diode lasers - experiments with fabry-perot cavities", by Boyd, Bliss, Libbrecht, 1996 http://www.its.caltech.edu/~atomic/publist/cavity.pdf [6] "Mode stability of external cavity diode lasers", by Saliba, Junker, Turner, Scholten, 2009 http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-48-35-6692 -- 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-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On 12 January 2015 at 12:34, Attila Kinali wrote: > Hi, > > I just stumbled over this [1] nice article by Fritz Riehle that might be > of interest to others as well. > > Attila Kinali > > [1] "Towards a Re-definition of the Second Based on Optical Atomic Clocks", > by Fritz Riehle, 2015 > http://arxiv.org/abs/1501.02068 I had a brief read. Equation 1 made me wonder what could be achieved with a cheap HeNe laser. It should be fairly easy to mix a couple of HeNe lasers on a photodiode and look at the difference frequency between them, so gaining insight into their stability. A quick check on Wikipedia https://en.wikipedia.org/wiki/Helium%E2%80%93neon_laser indicates a spectral width of 0.002 nm. The common 632.8 nm laser has a frequency of 4.7 x 10^14 Hz, or 470 THz. Of course I'm not suggesting a HeNe would provide the stability of cutting edge research laser optical clock, but they are easily within the budget of a hobbyist and could be a bit of fun to try to measure their stability/phase noise. The tricky bit would be getting 470 THz down to 10 MHz, but a cheap and quick experiment would prove whether it is a total waste of time or not. Dave ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On 1/13/15 2:41 AM, Attila Kinali wrote: On Mon, 12 Jan 2015 20:09:45 + Gregory Maxwell wrote: One exception here is space qualified oscillators. For those you go to the JPL and ask them to help you. Actually, you want to go to Applied Physics Labs (APL).. they're the USO folks. At JPL we buy our space flight oscillators from the usual suspects. ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Mon, 12 Jan 2015 20:09:45 + Gregory Maxwell wrote: > On Mon, Jan 12, 2015 at 12:34 PM, Attila Kinali wrote: > > I just stumbled over this [1] nice article by Fritz Riehle that might be > > of interest to others as well. > > I've seen less discussion of non-atomic stable optical oscillators. > Most (all?) of these optical atomic standards are passive atomic > clocks and need a free running oscillator. The local oscillator is considered a solved problem in research. If you need something low noise and stable you either go to Oscilloquartz or to Wenzel and get one of ther OCXO. The only place where you have to be carefull is the Dick Effect, but that's well understood and people usually acount for it. One exception here is space qualified oscillators. For those you go to the JPL and ask them to help you. > Seems that the state of the art in stabilized lasers has improved a > lot lately, e.g. there are commercial available 1550nm devices which > have a <=3Hz line-width: http://stablelasers.com/products.html (well > on a short term basis, the medium term performance is not so > impressive) Laser stabilization, especially for quantum metrology is still an actively researched field. Current state of the art is IIRC 0.3Hz linewidth (sorry, cannot find the reference at the moment). Mid- and long term stability depends highly on the reference used. Current research is fucused mainly on special, low vibration structures made out of low expansion glass or silicon. And these cavities are usually put into a temperature controlled chamber in vacuum. > Considering the rarity and extreme cost of H-masers, or just really > exceptional quarts oscillators; might it be the case that optical LOs > start looking interesting for applications which just need stability > (or being steered by other sources; e.g. GPSDL)? Well, an 8607 costs more than a Rb-standard. Yes, the 8607 has lower close in phase noise and up to several 1000s it rivals the Rb, but handling it is much more difficult than handling an Rb. Also, if you want to buy one of those exceptionally low noise/high stable 8607's (those that go down into the 10^-14 range) you'd have to sell your car. But, if you buy a H-maser from SpectraTime, you get a 8607 for free ;-) There used to be quite some literature on how to build low noise quartz oscillators. Most of those books are out of print today. With two notable exceptions: "Discrete Oscillator Design: Linear, Nonlinear, Transient, and Noise Domains" by Randall Rhea, 2010 and "Understanding Quartz Crystals and Oscillators", by Ramon Cerda, 2014 I had a look at the book by Rhea, it looks quite well written and contains a lot of real world information, but is a bit weak on the more theoretical part (description of oscillation, noise sources,...) and thus on the on the why things are done that way. I didn't had the chance to buy Cerdas book yet. The UFFC has some of the older books online. You need to be registered to access them, though. There is also a lot of knowledge on quartz crystalls hidden in old papers, but going trough them is some serious work. On the topic of opto-electronic oscillators, those are technologically nice, but they are rather bulky. That's why they are mostly used in research projects for atomic clocks. Also getting them to do low phase noise is not that easy, and unlike quartz oscillators, there is not much literature about that. > (They can be down-converted to microwave frequencies using an optical > comb; a mode-locked laser whos pulses are phase locked to an incoming > beam.) That is actually the current trend. There was a paper by NIST last year on downconverting the beat frequency of an optical comb down to RF using a frequency divider chain. They managed to get noise measures that rival that of a good quartz oscillator at 5MHz. Ie at higher frequencies, it is actually better than what a quartz oscillator can deliver. (for some reason i have not archived that paper and google fails me) > Certainly just the local oscillator is _closer_ to something a > time-nut might experiment with than a complete optical atomic standard > (if still not quite in reach). Well, building a CPT based Rb vapor cell frequency standard should be feasible. Yes, it's not a primary standard, but should do the job for most :-) >From what i've read, using one of the MOT cells like those of Sachser Laser [1] one might even be able to build a primary standard. But my understanding of MOT is relatively weak and i cannot say how difficult it actually would be. But it would be definitly a fun project to try :-) But i agree, building one of those ion or neutral atomic standards is pretty much out of question on a hobby budget. Heck, even an optical frequency comb is difficult to build, at best. And buying them.. i think buying a good Rb is still cheaper. Attila Kinali [1] http://www.sacher-laser.com/home/lab-equipment/spectroscopy/reference_gas_and_vapor_cells/mot_c
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Mon, Jan 12, 2015 at 12:34 PM, Attila Kinali wrote: > I just stumbled over this [1] nice article by Fritz Riehle that might be > of interest to others as well. I've seen less discussion of non-atomic stable optical oscillators. Most (all?) of these optical atomic standards are passive atomic clocks and need a free running oscillator. Seems that the state of the art in stabilized lasers has improved a lot lately, e.g. there are commercial available 1550nm devices which have a <=3Hz line-width: http://stablelasers.com/products.html (well on a short term basis, the medium term performance is not so impressive) Considering the rarity and extreme cost of H-masers, or just really exceptional quarts oscillators; might it be the case that optical LOs start looking interesting for applications which just need stability (or being steered by other sources; e.g. GPSDL)? (They can be down-converted to microwave frequencies using an optical comb; a mode-locked laser whos pulses are phase locked to an incoming beam.) Certainly just the local oscillator is _closer_ to something a time-nut might experiment with than a complete optical atomic standard (if still not quite in reach). ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Mon, 12 Jan 2015 13:34:03 +0100 Attila Kinali wrote: > I just stumbled over this [1] nice article by Fritz Riehle that might be > of interest to others as well. And while we are at it: "2e-18 total uncertainty in an atomic clock", by T.L. Nicholson et.al., 2015 http://arxiv.org/abs/1412.8261 -- 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-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Current state of optical clocks and the definition of the second
Hi, I just stumbled over this [1] nice article by Fritz Riehle that might be of interest to others as well. Attila Kinali [1] "Towards a Re-definition of the Second Based on Optical Atomic Clocks", by Fritz Riehle, 2015 http://arxiv.org/abs/1501.02068 -- 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-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
