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The program relies on the concept of 'closing speed of light', as defined by SR. How COULD it be wrong? See? :-) Henri Wilson won't tell us what the result was the one time he tested his program with measured data of a known binary. All that beer hasn't cured your tendency to rave. And you still REFUSE to answer the question. Are you a politician? You sure duck questions like one. |
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"bz" wrote in message 98.139... "George Dishman" wrote in : "bz" wrote in message 98.139... "George Dishman" wrote in : .... Yes, but it also affects single photons. How? I don't know how, I only know it does for the reason above, interference effects affect the probability of photon distribution even with multi-wavelength path differences. I thought that the distribution of the double slit pattern depended on the wavelength of the photon, not the coherence length of the laser. The spacing between indiviual fringes depends on the wavelength. The extent of the screen over which the fringes have good contrast ratio depends on the coherence length. I found this: http://marcus.whitman.edu/~beckmk/QM/inter/inter.html You might find the link to the presentation interesting, but the red graph on that page illustrates what I mean, the variation from peak to trough reduces as you go further from the zero difference point. Eventually, when the path difference is much more than the coherence length, the two beams are unrelated and you get uniform illumination. One can even get a double slit pattern from an incoherent source, such as a lightbulb with a band pass filter. Yes, and the narrower the filter, the wider the region showing fringes. I know of one place that coherence length is important: laser holography. I wanted to build a color holographic camera, using 3 laser diodes. During the research I did on that project I found that it would be useless for taking holographic pictures of anything at a distance greater than the coherence length of the diodes. This ruled out a portable color camera. The key factor is path length difference. If you send the reference beam through a coil of fibre, the coherence length would affect the distance but the depth of field. You will get good contrast if the difference betwen the coil length and twice the distance to the subject is less than the coherence length. I still am not sure that the coherence length effects interference patterns for single photon experiments. See the link above. http://www.holo.com/holo/book/book6&7.html Thanks, another useful link. By the way, did you know that you [anyone] can build a lensless, laser that uses the nitrogen in the air at atmospheric pressure? http://repairfaq.ece.drexel.edu/sam/lasercn2.htm I haven't seen it done with N2 but the guys on the next bench to me in my final year were doing the same with CO2. They got the basics working by breathing through a tube into the cavity :-) [quote restored] However I also know that a single photon in the double slit experiment has a negligible probability of hitting a point where the path difference is 10.5 wavelengths if the coherence length is 1000 wavelengths. .... Is your statement from experimental data? I would like to read about the experiment. Nothing special, this is the first hit I got on Google: http://tinyurl.com/cknu7 a good dual slit, single photon experiment but I see nothing about coherence length having an effect on the pattern. No, I was just saying that a photon cannot be considered to be like a small train of waves (e.g. less than a few wavelengths) if it can interfere with itself with a path difference of many wavelengths. Coherence length only creates an upper limit which is specific to the experiemnt. I think that there may be some effect due to the thermal phonons of the slits interacting with the electron clouds at the edge of the slit and deflecting photons passing close to the edge. Could be, I'm not saying I know the mechanism but experiments like that above tell us something about single photons that seems to contradict the idea that it can be a single cycle or something close to that. Unless, in passing through the slit, it influences the various vibrations in the structures of the slits, kind of like seismic waves, passing through the earth, cause measurable effects at a distance. Again, I will decline to speculate. I think QED would provide an answer but I don't know what it is. Single photon RF experiments should produce similar results to single photon light experiments. A single photon, at say 100 GHz, is 0.3 cm in wavelength. It has 6.6e-23 joules of energy (making it hard to detect one, but perhaps in a cryogenic chamber, it could be done). A 5 mW transmitter puts out 7.5e19 photons per second. In a single cycle, 7.54e8 photons are emitted at that power level. Assuming we could switch the transmitter on and off (or switch antenna and dummy load) at zero crossing, fast enough to pass only 1 cycle to the antenna, we would need to switch at a 10 ps interval. That should be possible. At 5 mW, it should give us 7.5e8 photons that are frequency and phase coherent, and, I predict, no keying transients. In any case, we should be able to determine the maximum length of a photon. I think I would be tempted to switch a current through a communications laser diode to do this at reasonable cost. The higher energy reduces the number of photons per mW and current can be easily controlled. The harder part would be the detector, PMT's are expensive. George |
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"George Dishman" wrote in
: "bz" wrote in message 98.139... "George Dishman" wrote in : "bz" wrote in message 98.139... "George Dishman" wrote in : ... Yes, but it also affects single photons. How? I don't know how, I only know it does for the reason above, interference effects affect the probability of photon distribution even with multi-wavelength path differences. I thought that the distribution of the double slit pattern depended on the wavelength of the photon, not the coherence length of the laser. The spacing between indiviual fringes depends on the wavelength. The extent of the screen over which the fringes have good contrast ratio depends on the coherence length. I found this: http://marcus.whitman.edu/~beckmk/QM/inter/inter.html You might find the link to the presentation interesting, but the red graph on that page illustrates what I mean, the variation from peak to trough reduces as you go further from the zero difference point. Eventually, when the path difference is much more than the coherence length, the two beams are unrelated and you get uniform illumination. Interesting, for sure. One can even get a double slit pattern from an incoherent source, such as a lightbulb with a band pass filter. Yes, and the narrower the filter, the wider the region showing fringes. Sounds like it should be related to information theory and s/n ratios Narrower bandwidth, better signal to noise ratio. I know of one place that coherence length is important: laser holography. I wanted to build a color holographic camera, using 3 laser diodes. During the research I did on that project I found that it would be useless for taking holographic pictures of anything at a distance greater than the coherence length of the diodes. This ruled out a portable color camera. The key factor is path length difference. If you send the reference beam through a coil of fibre, the coherence length would [not] affect the distance but the depth of field. You will get good contrast if the difference betwen the coil length and twice the distance to the subject is less than the coherence length. hmmmm. Path length difference. Interesting. Still, most laser diodes have rather short coherence lengths (on the order of a few hundred micrometers), giving a rather shallow depth of field. In 1997 'Long coherence length Laser diodes' meant 'several centimeters'. http://omlc.ogi.edu/news/dec97/pclaser.html I still am not sure that the coherence length effects interference patterns for single photon experiments. See the link above. http://www.holo.com/holo/book/book6&7.html Thanks, another useful link. By the way, did you know that you [anyone] can build a lensless, laser that uses the nitrogen in the air at atmospheric pressure? http://repairfaq.ece.drexel.edu/sam/lasercn2.htm I haven't seen it done with N2 but the guys on the next bench to me in my final year were doing the same with CO2. They got the basics working by breathing through a tube into the cavity :-) I was in college in the mid 60's and tried to help a kid with his high school science project, he built a HeNe laser but we never could get it to lase. That was my first experience with lasers. [quote restored] However I also know that a single photon in the double slit experiment has a negligible probability of hitting a point where the path difference is 10.5 wavelengths if the coherence length is 1000 wavelengths. ... Is your statement from experimental data? I would like to read about the experiment. Nothing special, this is the first hit I got on Google: http://tinyurl.com/cknu7 a good dual slit, single photon experiment but I see nothing about coherence length having an effect on the pattern. No, I was just saying that a photon cannot be considered to be like a small train of waves (e.g. less than a few wavelengths) if it can interfere with itself with a path difference of many wavelengths. Coherence length only creates an upper limit which is specific to the experiemnt. Minimum pulse lengths of ~ 1 cycle and single photon, dual slot interference patterns present an interesting challenge to the models for photons. I think that there may be some effect due to the thermal phonons of the slits interacting with the electron clouds at the edge of the slit and deflecting photons passing close to the edge. Could be, I'm not saying I know the mechanism but experiments like that above tell us something about single photons that seems to contradict the idea that it can be a single cycle or something close to that. Unless, in passing through the slit, it influences the various vibrations in the structures of the slits, kind of like seismic waves, passing through the earth, cause measurable effects at a distance. Again, I will decline to speculate. I think QED would provide an answer but I don't know what it is. I have reservations about Feynman's multipath theory. Single photon RF experiments should produce similar results to single photon light experiments. A single photon, at say 100 GHz, is 0.3 cm in wavelength. It has 6.6e-23 joules of energy (making it hard to detect one, but perhaps in a cryogenic chamber, it could be done). A 5 mW transmitter puts out 7.5e19 photons per second. In a single cycle, 7.54e8 photons are emitted at that power level. Assuming we could switch the transmitter on and off (or switch antenna and dummy load) at zero crossing, fast enough to pass only 1 cycle to the antenna, we would need to switch at a 10 ps interval. That should be possible. At 5 mW, it should give us 7.5e8 photons that are frequency and phase coherent, and, I predict, no keying transients. In any case, we should be able to determine the maximum length of a photon. I think I would be tempted to switch a current through a communications laser diode to do this at reasonable cost. But up in frequency mean the time resolution/switching speeds need to increase. The higher energy reduces the number of photons per mW and current can be easily controlled. The harder part would be the detector, PMT's are expensive. CCD detectors, such as in a video camera, are very sensitive now. -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. remove ch100-5 to avoid spam trap |
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bz wrote: "George Dishman" wrote in : much snipped The key factor is path length difference. If you send the reference beam through a coil of fibre, the coherence length would [not] affect the distance but the depth of field. You will get good contrast if the difference betwen the coil length and twice the distance to the subject is less than the coherence length. hmmmm. Path length difference. Interesting. Still, most laser diodes have rather short coherence lengths (on the order of a few hundred micrometers), giving a rather shallow depth of field. In 1997 'Long coherence length Laser diodes' meant 'several centimeters'. http://omlc.ogi.edu/news/dec97/pclaser.html It doesn't seem to have improved much but it would perhaps allow 3D filming of say insect flight with a depth of field of a few cm at a range of say 1m. more snpped Again, I will decline to speculate. I think QED would provide an answer but I don't know what it is. I have reservations about Feynman's multipath theory. It illustrates well how science need not provide understandable explanations. It works, just turn the handle and get the numbers, but thinking about the philosophical implications can be hazardous! I think I would be tempted to switch a current through a communications laser diode to do this at reasonable cost. But up in frequency mean the time resolution/switching speeds need to increase. Higher carrier frequency means a lower photon rate for the same power hence lower switching speeds to select a single photon. It would be possible to measure the bandwidth of a laser diode with coherence length in the cm range going through a shutter which was open for say 1 microsecond at a repetition rate of 10 kHz with a photon rate of a few hundred per second. The chances of getting two photons during an opening would be low but the shutter would be open for a time much longer than the "duration" of a single photon. Then change to a shutter open time around 10ps and see if the bandwidth increases. The photon "length" should be 30ps per cm of coherence so selecting only part of the photon should increase the bandwidth if I am right. The higher energy reduces the number of photons per mW and current can be easily controlled. The harder part would be the detector, PMT's are expensive. CCD detectors, such as in a video camera, are very sensitive now. That and a decent diffraction grating would do it but I guess the CCD would need to be cooled. George |
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" wrote in
ups.com: bz wrote: "George Dishman" wrote in : much snipped The key factor is path length difference. If you send the reference beam through a coil of fibre, the coherence length would [not] affect the distance but the depth of field. You will get good contrast if the difference betwen the coil length and twice the distance to the subject is less than the coherence length. hmmmm. Path length difference. Interesting. Still, most laser diodes have rather short coherence lengths (on the order of a few hundred micrometers), giving a rather shallow depth of field. In 1997 'Long coherence length Laser diodes' meant 'several centimeters'. http://omlc.ogi.edu/news/dec97/pclaser.html It doesn't seem to have improved much but it would perhaps allow 3D filming of say insect flight with a depth of field of a few cm at a range of say 1m. That would be interesting, especially in color. more snpped Again, I will decline to speculate. I think QED would provide an answer but I don't know what it is. I have reservations about Feynman's multipath theory. It illustrates well how science need not provide understandable explanations. It works, just turn the handle and get the numbers, but thinking about the philosophical implications can be hazardous! I have a hard time integrating it into my personality. I think I would be tempted to switch a current through a communications laser diode to do this at reasonable cost. But up in frequency mean the time resolution/switching speeds need to increase. Higher carrier frequency means a lower photon rate for the same power hence lower switching speeds to select a single photon. The way to test the photon 'length' is by switching times on the order of the expected time for the expected number of cycles per photon. It would be possible to measure the bandwidth of a laser diode with coherence length in the cm range going through a shutter which was open for say 1 microsecond at a repetition rate of 10 kHz with a photon rate of a few hundred per second. That would tell us nothing about the length of the photons. We can already get single photons by attenuating the beam intensity. Besides, spectrum analysis is done, every day, on fiber optical lasers. We know that for switching speeds used for gigabit data rates, the bandwidths needed are consistent with information theory. We need to push the envelope, so to speak, and see what happens with VERY narrow pulses, so narrow that they can only contain a single cycle. The chances of getting two photons during an opening would be low but the shutter would be open for a time much longer than the "duration" of a single photon. Then change to a shutter open time around 10ps and see if the bandwidth increases. The photon "length" should be 30ps per cm of coherence so selecting only part of the photon should increase the bandwidth if I am right. Selecting only part of the photon should either (1) produce no output or (2) produce a photon with less energy, since part of its energy has been absorbed. (1) is consistent with Einstein. (2) would blow all kinds of holes in quantum electro dynamics unless it could be shown to be consistent with the compton effect. The higher energy reduces the number of photons per mW and current can be easily controlled. The harder part would be the detector, PMT's are expensive. CCD detectors, such as in a video camera, are very sensitive now. That and a decent diffraction grating would do it but I guess the CCD would need to be cooled. We used Peltier coolers to cool the PMTubes in our NOx monitors, back when I did instrument repair for a division of Borg Warner. On the other hand, liquid nitrogen is pretty cheap. Liquid He is a bit pricy. But I could 'borrow a cup' of either as we use both in our building. [aside: when the new superconductor magnet for our new 700 MHz NMR was being brought up to field, they had a quench incident that boiled off 2000 litres of liquid helium in a few seconds. The fog in the air set off the fire alarms and cleared the building.] -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. remove ch100-5 to avoid spam trap |
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On Wed, 20 Jul 2005 14:10:59 GMT, Aristotle
wrote: The program relies on the concept of 'closing speed of light', as defined by SR. How COULD it be wrong? See? :-) Henri Wilson won't tell us what the result was the one time he tested his program with measured data of a known binary. All that beer hasn't cured your tendency to rave. And you still REFUSE to answer the question. Are you a politician? You sure duck questions like one. I have answered Andersen's question so many times that he has even forgotten what the question was. Notice that he and his mates have run for cover over my proof that the mythical 'GR correction' of GPS clocks if plain nonsense from start to finish. HW. www.users.bigpond.com/hewn/index.htm Sometimes I feel like a complete failure. The most useful thing I have ever done is prove Einstein wrong. |
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"bz" wrote in message 98.139... " wrote in ups.com: snip It would be possible to measure the bandwidth of a laser diode with coherence length in the cm range going through a shutter which was open for say 1 microsecond at a repetition rate of 10 kHz with a photon rate of a few hundred per second. That would tell us nothing about the length of the photons. We can already get single photons by attenuating the beam intensity. Besides, spectrum analysis is done, every day, on fiber optical lasers. We know that for switching speeds used for gigabit data rates, the bandwidths needed are consistent with information theory. Indeed, I was outlining the control experiment. We need to push the envelope, so to speak, and see what happens with VERY narrow pulses, so narrow that they can only contain a single cycle. Single cycle might be beyond the technology but chopping within the coherence length is achievable. The chances of getting two photons during an opening would be low but the shutter would be open for a time much longer than the "duration" of a single photon. Then change to a shutter open time around 10ps and see if the bandwidth increases. The photon "length" should be 30ps per cm of coherence so selecting only part of the photon should increase the bandwidth if I am right. Selecting only part of the photon should either (1) produce no output or (2) produce a photon with less energy, since part of its energy has been absorbed. (1) is consistent with Einstein. (2) would blow all kinds of holes in quantum electro dynamics unless it could be shown to be consistent with the compton effect. (1) A gate of 10ps at 10kHz should allow through 100 photons per billion so the intensity would be reduced by that factor. The laser intensity could be increased to partly compensate as long as the probability of two photons per gate remains negligible. (2) My expectation is that the mean photon energy would not change but the spread would increase. A coherence length of say 3cm is 100ps or a bandwidth of 20 GHz (both sidebands). Chopping it at 10ps would widen that to 200GHz creating photons with energies farther from the mean if I am right. [aside: when the new superconductor magnet for our new 700 MHz NMR was being brought up to field, they had a quench incident that boiled off 2000 litres of liquid helium in a few seconds. The fog in the air set off the fire alarms and cleared the building.] You guys sure have some fun :-) George |
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"George Dishman" wrote in news:dbr8pg$miv$1
@news.freedom2surf.net: "bz" wrote in message 98.139... " wrote in ups.com: snip It would be possible to measure the bandwidth of a laser diode with coherence length in the cm range going through a shutter which was open for say 1 microsecond at a repetition rate of 10 kHz with a photon rate of a few hundred per second. That would tell us nothing about the length of the photons. We can already get single photons by attenuating the beam intensity. Besides, spectrum analysis is done, every day, on fiber optical lasers. We know that for switching speeds used for gigabit data rates, the bandwidths needed are consistent with information theory. Indeed, I was outlining the control experiment. We need to push the envelope, so to speak, and see what happens with VERY narrow pulses, so narrow that they can only contain a single cycle. Single cycle might be beyond the technology but chopping within the coherence length is achievable. Single cycle is certainly not beyond the technology at lower frequencies. The chances of getting two photons during an opening would be low but the shutter would be open for a time much longer than the "duration" of a single photon. Then change to a shutter open time around 10ps and see if the bandwidth increases. The photon "length" should be 30ps per cm of coherence so selecting only part of the photon should increase the bandwidth if I am right. Selecting only part of the photon should either (1) produce no output or (2) produce a photon with less energy, since part of its energy has been absorbed. (1) is consistent with Einstein. (2) would blow all kinds of holes in quantum electro dynamics unless it could be shown to be consistent with the compton effect. Looks like people are, or think they are, making single photons. http://ipeqwww.epfl.ch/qd/html/singleqddevices.htm http://www.quiprocone.org/report034.pdf http://www.mqc2.it/MQC204/Stevenson.pdf http://cua.mit.edu/8.422/PHYSICS-vuc...omon-yamamoto- enhanced-single-photon-emission-from-a-quantum-dot-in-a-micropost- microcavity-apl-v82-p3596-2003-single_photons_APL_May03-1.pdf http://www.iota.u-psud.fr/~S4P/pdf%20files/APL02865.pdf (1) A gate of 10ps at 10kHz should allow through 100 photons per billion so the intensity would be reduced by that factor. The laser intensity could be increased to partly compensate as long as the probability of two photons per gate remains negligible. (2) My expectation is that the mean photon energy would not change but the spread would increase. A coherence length of say 3cm is 100ps or a bandwidth of 20 GHz (both sidebands). Chopping it at 10ps would widen that to 200GHz creating photons with energies farther from the mean if I am right. [aside: when the new superconductor magnet for our new 700 MHz NMR was being brought up to field, they had a quench incident that boiled off 2000 litres of liquid helium in a few seconds. The fog in the air set off the fire alarms and cleared the building.] You guys sure have some fun :-) George -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. remove ch100-5 to avoid spam trap |
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"bz" wrote in message 98.139... "George Dishman" wrote in news:dbr8pg$miv$1 @news.freedom2surf.net: "bz" wrote in message 98.139... " wrote in ups.com: snip We need to push the envelope, so to speak, and see what happens with VERY narrow pulses, so narrow that they can only contain a single cycle. Single cycle might be beyond the technology but chopping within the coherence length is achievable. Single cycle is certainly not beyond the technology at lower frequencies. No but I think measuring single photons becomes harder. Looks like people are, or think they are, making single photons. http://ipeqwww.epfl.ch/qd/html/singleqddevices.htm http://www.quiprocone.org/report034.pdf http://www.mqc2.it/MQC204/Stevenson.pdf http://cua.mit.edu/8.422/PHYSICS-vuc...omon-yamamoto- enhanced-single-photon-emission-from-a-quantum-dot-in-a-micropost- microcavity-apl-v82-p3596-2003-single_photons_APL_May03-1.pdf http://www.iota.u-psud.fr/~S4P/pdf%20files/APL02865.pdf We are certainly on the verge of moving to verge of handling single photons routinely. Thanks again for the links. George |
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"bz" wrote in message 98.139... | "George Dishman" wrote in news:dbr8pg$miv$1 | @news.freedom2surf.net: Watch our for bz. He'll calculate 76.6c for the speed of an electron in an accelerator and blame YOU for it. Androcles. |
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