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Natural Science Forum / Physics / Optics / December 2004Optics Idea Beauty Contest
Dear All: It's the end of the year and all, and since we apparently have absolutely nothing of interest to talk about these days--troll-feeding frenzies apart--I'd like to know what your favourite pretty optical or electro-optical tricks are. My bias is towards measurements, but design ideas would be fine too. Please include a few sentences on just what the idea is, and why it's so pretty. My all-time favourite is two-photon Doppler-free spectroscopy, where you shine two beams from the same laser in antiparallel directions, chop them at different frequencies, and detect the fluorescence at |f1 +- f2|. To make these components, an atom has to have absorbed a photon from each beam, one upshifted and one downshifted by the axial motion of the atom. This results in a spectrum that is limited by the natural line width and transit time, but shows no first-order Doppler broadening whatever. A good second is the photochemical grating, where an interference pattern in the pump beams produces a grating in the sample, which diffracts a probe beam in a known direction. Zero background, highly selective, and very pretty. How about yours? Cheers, Phil Hobbs > Dear All: > [quoted text clipped - 3 lines] > electro-optical tricks are. My bias is towards measurements, but design > ideas would be fine too. Please include a few sentences on just what > the idea is, and why it's so pretty. > > My all-time favourite is two-photon Doppler-free spectroscopy, where you > shine two beams from the same laser in antiparallel directions, chop > them at different frequencies, and detect the fluorescence at |f1 +- > f2|. To make these components, an atom has to have absorbed a photon > from each beam, one upshifted and one downshifted by the axial motion of > the atom. This results in a spectrum that is limited by the natural [quoted text clipped - 4 lines] > pattern in the pump beams produces a grating in the sample, which > diffracts a probe beam in a known direction. Zero background, highly > selective, and very pretty. > [quoted text clipped - 3 lines] > > Phil Hobbs Hi Phil, Pretty? Hmm. Not sure if I would have used that word. Elegant, perhaps. Cool, also. Regardless, *my* all time favorite is a two-beam method of measuring the Kerr rotation of a magneto-optic disc that is independent of the orientation of the optic axis of the birefringent substrate (usually polycarbonate or PMMA), and only very mildly dependent on the magnitude of the retardation. I'm biased, of course, because it's my invention. See U.S. patent #5,694,384. :) Also, probably no one else has ever heard of it. As for something that other people actually know about: One of my favorites has always been the fiber-optic rotation rate sensor based on the Sagnac effect. The obvious best known product is the fiber optic gyroscope (FOG). I remember I was in school at Pasadena City College many, many years ago,taking part in their laser optics program when I first read about FOGs. I thought, "Holy crap is that cool!" Yes, it's old news, but still remarkably elegant AND useful. Speaking of the PCC laser optics program, does anyone know if that still exists? When I went, Dr. Wai Min Liu (sp?) had just started it a couple years before. He was simultaneously working at JPL. In fact, most of the instructors were professionals working in industry, which is one of the reasons I think the program worked so well. Spencer > > selective, and very pretty. > > [quoted text clipped - 3 lines] > > > > Phil Hobbs Seems to that the simplicity and effectiveness of Kerr lens mode locking technique is pretty elegant. Also, Ted Haensch's (and was Jan Hall also in on this?) schemes for locking up an optical frequency comb so that it extrapolates down to *exactly* DC, rather than to some arbitrary offset from DC. Quantum cascade laser is a bit complex to explain but turns out to be pretty neat. Steve Harris' EIT (electromagnetically induced transparency), LWI (lasers without inversion),and slow light. Bob Byer's NPRO (non-planar ring oscillator) YAG lasers. "Table-top terawatt" lasers from Gerard Mourou and predecessors. > Also, Ted Haensch's (and was Jan Hall also in on this?) schemes for > locking up an optical frequency comb so that it extrapolates down to > *exactly* DC, rather than to some arbitrary offset from DC. I think that's ***Theo*** Haensch > "Table-top terawatt" lasers from Gerard Mourou and predecessors. > I think that's ***Theo*** Haensch WIdely called Ted, however. > > I think that's ***Theo*** Haensch > > Widely called Ted, however. My apologies, you know those things infinitely better than I do. (I just go by the name of the author of many papers, I have no personal acquaintance with him.) If Theo stands for Theodor, and if Ted is a sub-nickname for Theo, let's introduce the "Ted Scheimpflug" condition or rule. ;-) <snip> > Speaking of the PCC laser optics program, does anyone know if that > still exists? When I went, Dr. Wai Min Liu (sp?) had just started it a [quoted text clipped - 3 lines] > > Spencer I went to Citrus College optics classes in Azusa in 1972-3 (Jim Kent - instructor), and Dr. Liu taught optical design classes at night. Leonard Larks (JPL) and Milt Laikin also visited our classes. I think Dr. Liu was at Xerox at the time, but could be mistaken. Is he still active in optics? Mike > Dear All: > It's the end of the year and all, and since we apparently have [quoted text clipped - 3 lines] > ideas would be fine too. Please include a few sentences on just what > the idea is, and why it's so pretty. At one time I thought those "X-Ray Glasses" in comic book advertisements were potentially the neatest things. Alas. (Someone later suggested 'shoe mirrors', but I thought that was too crude.) In both cases "why pretty" is best left as an exercise to the reader. A unique item I've seen is an approx. 3 inch cube of clear plastic with little spots of IR-sensitive material scattered throughout. It would allow one to see beams of IR coming in. Would like to scan a focused beam to make images (the 'why pretty'), but work, chores, newsgroup posting, etc. tends to chew up available play time. So right now, my favourite trick to see is what NASA will do to service HST to keep it alive beyond the next couple years. These are all interesting techniques. I'd also have to give a nod to ultrashort pulse characterization techniques, such as FROG (frequency resolved optical gating; Rick Trebino), SPIDER (spectral phase interferometry for direct electric field reconstruction - Ian Walmsley) and their variants, which provide both the amplitude and phase profiles of optical pulses in an unambiguous manner. For a beauty contest, FROG would have to win - the data sets lend themselves to very nice pictures. See for instance http://www.physics.gatech.edu/gcuo/gallery.html Frank > Dear All: > [quoted text clipped - 24 lines] > > Phil Hobbs I'll cast a vote for the "liquid lens" > I'll cast a vote for the "liquid lens" Which one, the Philips one or the one from the company which is suing Philips? the idea... I've yet to see a physical manifestation that gets me where I want to be, but I can continue to hope > > I'll cast a vote for the "liquid lens" > > Which one, the Philips one or the one from the company which is suing > Philips? > the idea... I've yet to see a physical manifestation that gets me where I > want to be, but I can continue to hope... Hope springs eternal. What do you want? Maybe you could explain. We are goofing off anyway. But please, please no mention of some elaborate zoom with several liquid lenses. My earliest knowledge of a liquid lens was patented years ago. It's use was for eyeglasses with a vaiable focal length. One could pump liquid from a bladder to increase the curvature of one surface of a flexible cell.. > My earliest knowledge of a liquid lens was patented years ago. It's > use was for eyeglasses with a vaiable focal length. One could pump > liquid from a bladder to increase the curvature of one surface of a > flexible cell.. Purely personal opinion re liquid lens: Basic concept of a liquid lens, with or without inflatable bladder or some kind of stretchable membrane or whatever, seems pretty trivial and obvious to me -- I wouldn't call it a beautiful or even particularly clever idea. On the other hand if someone can come up with a particular application where the liquid lens really solves a specific problem and meets a real need, in a way that's notably effective, elegant, economical, _and better than any other solution_ -- now that _would_ deserve praise. Is there such an example? One candidate: Roger Angell in Arizona dumps ??? tons of glass chips into what looks like one of those backyard above-ground swimming pools a meter deep and 3 or 4 meters across, with electric heaters in the walls and bottom; puts this on a rotating platform (located underneath the Univ of Ariz football stadium) with the heaters fed thru high-current slip rings; slowly spins the platform while he melts the glass until the surface forms into a more or less perfect deeply curved 3 or 4 meter diamater mirror surface (could be called a liquid lens, right?); then cools it equally slowly (still rotating, of course) until it solidifies into that shape. [Would take forever to "hog out" all the glass needed to create the same mirror shape, then double-forever to polish it to needed perfection.] As an added fillip, he stands up a lot of hexagonal sandstone posts in a regular array in the swimming pool before the glass chips are added, with varying heights that come up almost to the final mirror surface. When the mirror is done, blast out these sandstone segments with a high-pressure water hose, and you have a much lighter-weight, highly rigid and stable honeycomb backing for your one or two-foot thick mirror. Now _that's_ a beautiful optics accomplishment. >AES/newspost <sieg...@stanford.edu> >>rrl...@yahoo.com wrote: >> My earliest knowledge of a liquid lens was patented years ago. It's >> use was for eyeglasses with a vaiable focal length. One could pump >> liquid from a bladder to increase the curvature of one surface of a >> flexible cell.. >Purely personal opinion re liquid lens: Basic concept of a liquid lens, >with or without inflatable bladder or some kind of stretchable membrane >or whatever, seems pretty trivial and obvious to me -- I wouldn't call >>t a beautiful or even particularly clever idea. You might consider it elegant if the bending part of the liquid lens was not planar. This results in a tunable asphericity. > > My earliest knowledge of a liquid lens was patented years ago. It's > > use was for eyeglasses with a vaiable focal length. One could pump [quoted text clipped - 34 lines] > > Now _that's_ a beautiful optics accomplishment. A group at Philips Research Eindhoven in the Netherlands is developing an electrically adjustable liquid lens with one application being miniaturized autofocus for phone-cams. http://www.photonics.com/spectra/tech/XQ/ASP/techid.1658/QX/read.htm The claim is that it can be build much smaller and cheaper than a conventional mechanical focusing mechanism. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. AES wrote: > "One candidate: Roger Angell in Arizona dumps ??? tons of glass chips into what looks like one of those backyard above-ground swimming pools a meter deep and 3 or 4 meters across, with electric heaters in the walls and bottom; puts this on a rotating platform (located underneath the Univ of Ariz football stadium) with the heaters fed thru high-current slip rings; slowly spins the platform while he melts the glass until the surface forms into a more or less perfect deeply curved 3 or 4 meter diamater mirror surface (could be called a liquid lens, right?); then cools it equally slowly (still rotating, of course) until it solidifies into that shape." If we're going to go that route, then molded plastic lenses are up there too, since the plastic had to be melted in order to mold it. How about an application where the liquid is a liquid while the lens is in actual use? I'll nominate the eye as a work of optical beauty. Phil, Would you be up for collecting these ideas, and writing a little piece for OPN on this theme, giving some of the best responses? It would be well received. Seriously, AES I'll second that. -- Mark AES wrote: Phil, Would you be up for collecting these ideas, and writing a little piece for OPN on this theme, giving some of the best responses? It would be well received. Seriously, AES <snip>> > How about yours? > > Cheers, > > Phil Hobbs Years ago Hewlett Packard made a distance measuring interferometer using a corner cube, which had a resolution (I think) of about 1 micron over several metres range. They needed two closely spaced wavelengths to cover this range, and they didn't have all the lasers we have today, so they used a magnet to Zeeman split the HeNe 633 nm laser line. I call that beautiful. Brian > Years ago Hewlett Packard made a distance measuring interferometer using a > corner cube, which had a resolution (I think) of about 1 micron over several > metres range. They needed two closely spaced wavelengths to cover this > range, and they didn't have all the lasers we have today, so they used a > magnet to Zeeman split the HeNe 633 nm laser line. I call that beautiful. Very neat indeed but 1967 (HP) vintage as far as I recall Philips tried to beat them at about the same time with a gadget that put in front of a single mode stabilized He-Ne laser produced a (low frequency) uniformly rotating polarization vector which you can decompose into two contra-rotating polarization vectors (i.e. circularly polarized) which a quarter wave plate transformed into two orthogonal linearly polarized vibrations with a slight frequency difference between them (of the order of 2 MHz, same frequency as before). Look up the Philips scientific literature of the time. The analysis of the above gadget was an elaborate (but delightful for the aficionados) exercise in the use of Jones matrices. Now for this Zeeman effect business it was done for the first time (early 1965) by a Mr./Dr. Millikan. (yes Millikan, not "oil-drop" Millikan, but his nephew) at some lab, south of Paris. I remember visiting this lab and being rather impressed. It did not dawn on us at the time that this could have an interferometric application. What we had in mind was the isotopic separation spectroscopy of UF6. > Philips tried to beat them at about the same time with a gadget that put in > front of a single mode stabilized He-Ne laser produced a (low frequency) [quoted text clipped - 5 lines] > > Look up the Philips scientific literature of the time. A microwave variant of this was a circular waveguide that propagated degenerate TE waves with E_x and E_y polarization. Inserting a section that was slightly elliptical or had a dielectric slab that broke the x-y degeneracy and rotating this mechanically created a low-frequency (*very* low-frequency) splitting between the two polarizations. So, it's electric-dipole rather than magnetic-dipole, and microwave rather than optical, and mechanical rather electro-optical modulation -- but what the heck, "rotation is rotation". Not sure if this was ever really used in a practical system -- digging back into the Rad Lab Series might supply the answer. > <snip>> > > How about yours? [quoted text clipped - 10 lines] > > Brian It really was very clever, laser-wise and interferometer-wise. The Zeeman splitting part was really quite sophisticated; it involved having two adjacent axial modes oscillating simultaneous in orthogonal polarizations, so they could be could be used simultaneously in the interferometer, with their mean wavelength drift cancelled out -- and the ratio of the intensities of the two polarizations could be used to stabilize both of them to the He-Ne line center. > It really was very clever, laser-wise and interferometer-wise. The > Zeeman splitting part was really quite sophisticated; it involved having [quoted text clipped - 3 lines] > the ratio of the intensities of the two polarizations could be used to > stabilize both of them to the He-Ne line center. When I had need for DME equipment in the middle to late 1970's, I looked at available DME equipment. I did not run across actual laser interferometry for use in surveying. The reply I gave earlier did not consider these Zeeman devices. The surveying DME all used radio frequency interferometry with radio modulation of the optical carrier. The ones using lasers had a big noise problem arising from atmospheric scintillation. Broader band LED devices were not as troublesome. Bill > > [quoted text clipped - 25 lines] >stabilize both of them to the He-Ne line center. > They phaselocked the beat note to a quartz oscillator, using the coil current as the control input, thereby reducing the measurement bandwidth and keeping the fringe counting stable. A quarter-wave plate and polarizing beamsplitter produced sine and cosine outputs from two detectors, to get the direction. A good choice, I think. Nowadays you'd probably do the same thing using modulation-generated carrier and a diode laser, though you probably wouldn't get the same stability. Actually, the modulation-generated carrier idea is another beauty contestant--it uses the 90 degree phase shift between even and odd order FM sidebands to get 0 and 90 degree measurements nearly for free--without needing two detectors, even. I invented it independently about 4 years after it was first published, and was a bit crestfallen to find it so well known already. That doesn't happen to me very often--but another time (as a grad student)I sent my one attempt at a purely theoretical paper in to JOSA A, only to discover that much of it had been anticipated by Lord Rayleigh. One of my less merciful colleagues asked me how it felt to be in the forefront of 19th century science. ;-( (Fortunately I discovered it myself, instead of the referee. That would _really_ have been embarrassing.) Keep the good ideas coming, and maybe it will wind up in OPN, we'll see. I've been publishing more OPNs than journal articles lately, which is Not A Good Thing. Cheers, Phil Hobbs > >><snip>> > >> [quoted text clipped - 21 lines] > > polarizations could be used to stabilize both of them to the He-Ne > > line center. > They phaselocked the beat note to a quartz oscillator, using the coil > current as the control input, thereby reducing the measurement > bandwidth and keeping the fringe counting stable. A quarter-wave > plate and polarizing beamsplitter produced sine and cosine outputs > from two detectors, to get the direction. For the HP lasers, it wasn't two adjacent (normal) axial modes - which would have been order of 1 GHz apart - but the Zeeman frequency shift in the MHz range. Other frequency stabilized HeNe lasers do use two adjacent axial modes or a single axial mode feedback controlled to be on a certain portion of the gain curve. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. > A good choice, I think. Nowadays you'd probably do the same thing > using modulation-generated carrier and a diode laser, though you [quoted text clipped - 21 lines] > > Phil Hobbs As best I recall (but I don't have time to check right now), hp made both a tripod-mounted surveying instrument which used a diode laser which was rf modulated down in the range around 30 MHz (?), and a larger and considerably more expensive interferometer type distance measuring instrument which used a He-Ne laser oscillating in two orthogonally polarized axial modes spaced by a GHz or so underneath the weakly Zeeman-split line of the He-Ne laser. The r-f modulated surveying instrument -- or am I thinking of an instrument called the Geodolite, made by Coherent? -- would have in essence counted fringes in the meter range over distances up to a kilometer or more, and had a resolution equal to a small fraction of that. The He-Ne laser interferometer, used for metrology, precision machine tool work, and alignment of very high precision structures, counted optical fringes over distances from less than a meter up to maybe 10s of meters. I recall an issue of the hp Journal which described a fun experiment in which they projected the beam from on the He-Ne interferometers from a truck up to a corner cube on the top of Coit Tower in San Francisco and examined the spectrum of the resulting interferometer fringes with some new hp fast counter and Fourier transform instruments. The lowest order bending mode of Coit Tower turns out to be around 3 Hz, as I remember. > The r-f modulated surveying instrument -- or am I thinking of an > instrument called the Geodolite, made by Coherent? -- would have in > essence counted fringes in the meter range over distances up to a > kilometer or more, and had a resolution equal to a small fraction of > that. I believe that is correct. They used r-f phase detectors to interpolate counts and multiple frequencies to resolve range ambiguities. We ended up using a Wild instrument. In part, it was because they were willing to let us have schematics. We connected to IIRC seven segment displays and converted the displayed segments into decimal digits before going into a computer. These devices were proceeded microwave versions that were heavily used by surveyors even though they were heavy loads to carry. Bill > <snip>> >> How about yours? [quoted text clipped - 10 lines] > > Brian I think that you have that all wrong. The laser was a carrier for rf modulation. It was an rf interferometer with multiple frequencies used to resolve range ambiguity. Similar equipment was made by a number of companies under various tradenames using both coherent and incoherent optical carriers. Some names are tellurimter, geodimiter, and the generic distance mesuring equipment or DME. Bill > > <snip>> > >> How about yours? [quoted text clipped - 8 lines] > > range, and they didn't have all the lasers we have today, so they used a > > magnet to Zeeman split the HeNe 633 nm laser line. I call that beautiful. > > Brian > I think that you have that all wrong. The laser was a carrier for rf > modulation. It was an rf interferometer with multiple frequencies used to > resolve range ambiguity. Similar equipment was made by a number of companies > under various tradenames using both coherent and incoherent optical > carriers. The difference frequency has nothing to do with the range over which the instrument operates. It's a relative distance measurement. Agilent may still have versions of these systems using the same techniques. The lasers had model numbers like 5500, 5501, 5517, etc. I don't recall what the interferometers were called. The early ones were piezo stabilized while the later ones were thermally stabilized. The difference frequency was in the 1-2 MHz range and fixed for a given instrument. Resolution down to 10 nm was in the specs. More info on the HP lasers in: http://repairfaq.ece.drexel.edu/sam/laserlia.htm#liaint2f and on HP lasers in particular: http://repairfaq.ece.drexel.edu/sam/laserhen.htm#henish3 It's easy to do experiments of your own by Zeeman splitting a common HeNe laser tube: http://repairfaq.ece.drexel.edu/sam/laserchn.htm#chndzees --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. > Some names are tellurimter, geodimiter, and the generic distance mesuring > equipment or DME. For me one of the greatest inventions in optics was the achromatic doublet by Chester More Hall. This was at a time when there was very little optics knowledge available. He was not even a scientist but a barrister (lawyer). The achromatic design is so simple yet is one of the most important optical advances of all time. > For me one of the greatest inventions in optics was the achromatic > doublet by Chester More Hall. This was at a time when there was very > little optics knowledge available. He was not even a scientist but a > barrister (lawyer). The achromatic design is so simple yet is one of > the most important optical advances of all time. Sure, but how far back do we have to go? Here we are talking 250 yrs approx. Furthermore it is a very well known story. Interesting that this man was a lawyer, because he never attempted to obtain a patent, (at least not in due time), or whatever was the equivalent then. He contracted the components of the doublet to different opticians, Someone (Dollond?) got suspicious etc. His lack of diligence, as they are fond to say, ended up costing him dearly. He did contract the different componants of the doublet to two different opticians. However, they were eventually subcontracted to just one optician. The story goes that the optician put them together and realized that the pair were achromatic. I believe that Dolland was well aware of all this. He is acredited (probably correctly) as being the first to make achromatic instruments from this idea., As an aside, there is another story (I believe it to be correct) that the achromatic doublet was proposed years earlier by a student. However, Isaac Newton so ridiculed the idea that it did not reappear for many years later. Can anyone else spread light on this story? |
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