Arthur Ashkin Honored at FiO/LS

29. October 2010

By Patricia Daukantas

I can’t let my coverage of FiO/LS end without mentioning the wonderful talk that OSA Honorary Member Arthur Ashkin gave at the special symposium organized in his honor.

Ashkin, now 88 years old and retired from Alcatel-Lucent/Bell Laboratories (U.S.A.), pioneered the notion of moving microparticles with laser light, back in the days when lasers were the new thing on the lab bench. His work formed the basis for optical tweezers and, eventually, the atom-cooling and laser-trapping work that garnered three other OSA Honorary Members their Nobel Prize in 1997.

In his autobiographical speech, Ashkin--who still has traces of the accent of his native Brooklyn, N.Y.--showed his warm and sometimes mildly self-deprecating humor. Yes, he said, he holds degrees from “all these fancy schools” like Columbia and Cornell universities, but it took him seven years just to get his bachelor’s degree.

That wasn’t entirely of his own doing. As he entered Columbia, World War II was starting and the university, whose physics department had people like Sidney Millman, Willis Lamb and Polykarp Kusch, founded a radiation laboratory with, as Ashkin put it, “all this new equipment free from the government.” Millman taught the new undergraduate about magnetrons – “glass, brass and sealing wax” – and then Ashkin got drafted at age 19.

“I’m a sophomore, how important can I be to the war effort?” Ashkin asked rhetorically. But the folks at Columbia got him into the Army’s enlisted reserve, so that he could work as a staff member, and he eventually built a megawatt magnetron.

Once Ashkin got to Cornell as a graduate student, he said, he took no solid-state physics or optics courses. “All I took was nuclear physics because there were all these guys from Los Alamos [the Manhattan Project, which built the first nuclear weapons],” he said. He took the first quantum mechanics class taught by the then-future Nobel Prize winner Richard P. Feynman. Ashkin added: “The stories I could tell, if I had the time…”

Once hired at Bell Labs, he was told he could do anything he wanted to do, but he still ended up working on microwave tubes for a while. “At Bell Labs they wanted you to do great work, but you had to find your own way,” he said.

In the late 1960s, Ashkin attended a talk about “runners” and “bouncers,” or tiny balls moving around due to heating. That got him thinking about radiation pressure, and he started thinking about moving even tinier particles with the light from laser beams, and then experimenting in earnest.

By the time Ashkin was writing his first paper on the subject, he was wondering whether the laser beams could trap atoms, molecules and microscopic living things. “So I put all that into the paper and got credit for it,” he added. His first experiments with trying to move bacteria around killed them--he dubbed it “opticution”--but eventually he and his colleagues learned how to keep them alive while moving them with infrared beams.

You can read more about Ashkin’s pioneering efforts in a March 2010 feature article in OPN.

Like a good entertainer, Ashkin knows how to leave his audiences wanting more. He wound up his talk by saying that during his 15-year retirement, he has been experimenting with solar power, and he thinks he has found away of getting energy from the Sun more cheaply than burning fossil fuels.“I’m writing a paper for Science, and if I tell you about it they won’t publish it,” he concluded. “So stay tuned.”

The Newest OSA Honorary Member

At its meeting during FiO/LS, the OSA board of directors selected James P. Gordon as the Society’s newest Honorary Member. Regular readers of OPN may recall his article for the May 2010 issue of OPN--the special “Lasers at 50” issue--in which he described his work on the first maser with another OSA Honorary Member, Charles H. Townes.

2010-10 October, Applied optics, Biomedical optics, Frontiers in Optics, Optics history , , , , ,

FiO/LS Day Three: Cheers for Optical Communications

28. October 2010

By Patricia Daukantas

To celebrate Charles Kao’s share of the 2009 Nobel Prize in physics for his pioneering fiber optics work, the FiO/LS conference brought together industrial and academic researchers for a special symposium on optical communications.

OSA’s 1995 president, Tingye Li, kicked off the conference with a historical overview of the field that, as a longtime researcher at AT&T/Bell Laboratories (U.S.A.), he was well-positioned to witness and influence.

Noting that Kao’s Nobel came exactly 100 years after Guglielmo Marconi and Karl Ferdinand Braun won it for “wireless telegraphy,” Li said that the award to Kao fulfilled the original intent of the prize to recognize innovations that benefit human society. He listed Kao’s three great innovations:

  • Conceptualizing optical fiber communications by proposing glass fibers as a viable data-transmitting medium;
  • Having the insight that silica would be the low-loss medium of choice for future communications and rigorously verifying that experimentally, showing his understanding of the fundamental physics behind the application; and
  • Traveling around the world to spread his “gospel” of optical communications until the industry began to take it seriously.

 

Li noted the characteristic engineering language of Kao’s first paper on the subject in 1966. He wrote that silica fibers may have a “large information capacity,” when the correct adjectival phrase might have turned out to be “astronomically large.” After all, the capacity of optical fiber systems has multiplied 1-million-fold since Corning Inc. developed the first truly low-loss fiber in 1970 and the telecom industry started its early field trials shortly thereafter.

Other symposium speakers included Peter Schultz of Corning (U.S.A.), David Payne of the University of Southampton (England) and Hiroshi Takahashi of NTT Photonics Laboratories (Japan). (Shultz recently wrote an article for OPN about the development of the first low-loss optical fibers.)

Current OSA director-at-large Neal Bergano of Tyco Electronics (U.S.A.) capped off the symposium by describing the types of cable armor, repeaters and large ships that go into building the planet’s undersea communications infrastructure. Hundreds of thousands of kilometers of optical cables now stretch across ocean and sea floors, either as direct links or branch-and-trunk networks. They certainly transmit digital data for far less cost than the $5 per word for telegrams sent via the first permanent transatlantic telegraphic cable in the late 1860s.

More FiO/LS Coverage

Today (Thursday) is the final day of the conference, with a number of invited talks on intriguing topics.

I haven’t forgotten the OSA Student Chapter members whose competition I photographed -- watch for coverage in an upcoming blog post. Also, I wrote about OSA Fellow Michal Lipson’s talk at the MWOSA gathering in OPN’s Bright Futures Blog.

Fiber optics, FiO/LS, Frontiers in Optics, Optics history, OSA , , , , , , , , ,

Ole Rømer: Three Hundred Years of Light Speed

23. September 2010

By Patricia Daukantas

 

A recent article in the Washington Post pointed out something that OPN readers already know: A 17th-century Danish scientist was the first person to come up with a realistic estimate of the speed of light.

 

I wrote about this guy, Ole Rømer, in the July/August 2009 issue of OPN. Things get busy in the magazine business, though, so it took a contributing writer in the Post to point out that Rømer died 300 years ago this week – September 19, 1710.

 

 

As the Post writer and I both noted, Rømer deduced that light had a very large, but still finite, velocity by studying the motion of the moon Io around the planet Jupiter. After he published his findings in 1676, he turned his attention to other matters, and later scientists continued to refine their measurements of light’s speed until we got the standard that we have today.

 

One of the challenges that I – or anyone else – have faced when writing about Rømer is that many of his letters and other papers were burned in a building fire after his death. Thus, science historians have lost some valuable primary source material that would have given us additional insight into Rømer’s reasoning and his struggles to gain acceptance of his hypothesis. Still, we know enough about this Danish astronomer to commemorate his place on the timeline of scientific understanding.

2010-09 September, Optics history ,

AFOSR LaserFest Event Highlights Work of OSA Fellows

11. August 2010

By Christina Folz, OPN Managing Editor

On August 6, the Air Force Office of Scientific Research (AFOSR) continued the 2010 LaserFest celebration with its own event highlighting everyone's favorite technology this year. The event showcased the work of three OSA Fellows--Alan Willner, who works on optical communications at the University of Southern California; Margaret Murnane, who is studying high-peak-power physics with lasers at the University of Colorado, and Richard Miles, a Princeton professor who spoke about the role of lasers in aerospace. Two other laser experts--Robert Jones and Gary Teraney--described the important role that lasers are playing in the defense industry and in medicine. Each of the participants had been funded by AFOSR as grad students and went on to become distinguished leaders in the laser field.

For those who missed the event, or who simply sought more info, yesterday the AFOSR held a "bloggers roundtable" moderated by Howard Schlossberg, the program manager at AFOSR, to discuss the event and answer additional questions about the state-of-the art in laser technology. Schlossberg was joined by several of the event participants, including Willner and Miles.

And for those who missed THAT (including this humble blogger), you're in luck: A podcast and transcript of the roundtable are posted on the Department of Defense's blog

Schlossberg emphasized the importance of solid-state lasers in particular as pivotal to modern laser research and technology. "The primary emphasis by us and by others as well is in solid-state lasers, either on bulk solids, slabs pumped with semi-conducted lasers, or in optical fiber lasers," he said. He also called medical and materials processing two of the biggest application areas of lasers these days.

And don't worry--LaserFest is far from over. "At meetings, they'll have demonstrations and displays," Schlossberg said. "If you get on the LaserFest website, you'll see some of the terrific movies of early times." 

Party on!  

2010-08 August, Applied optics, Laserfest, Lasers, Optics history , , , , , , , ,

Happy (Belated) 95th Birthday, Charles Townes!

5. August 2010

By Patricia Daukantas

 

Last week, Charles H. Townes passed yet another milestone: he turned 95 years old.

 

Townes, now of the University of California at Berkeley (U.S.A.), is of course most famous in the optics community for his fundamental contributions to laser theory:

 

  • The development of the first maser with James Gordon and Herbert Zeiger in 1953, as Gordon recounted in a recent OPN feature article; and
  • The principles behind the optical maser, or laser, published by Townes and his brother-in-law, Arthur Schawlow, in December 1958.

Along the way, he’s worked at Bell Labs and three prominent universities, served on various U.S. government committees and think tanks, held a Guggenheim Fellowship and a Fulbright Scholarship, and won the Templeton Prize for contributing to the understanding of religion.

 

As we’ve noted in past OPN blog posts, Townes is still active in astrophysical research. So far in 2010, he and his colleagues have published two articles relating to Berkeley’s Infrared Spatial Interferometer, a three-telescope system with high spectral resolution. This year, which is the 50th anniversary of the first working laser, he’s been invited to speak at many scientific conferences, including a special historical symposium at CLEO/QELS 2010.

 

We should also note that 2010 marks two other milestones for Townes. It was 40 years ago, in 1970, that Townes was named an OSA Honorary Member. And it was 50 years ago that Townes, along with 14 other physicists, chemists, engineers and physicians, was named a representative of “U.S. Scientists” for Time magazine’s 1960 “Men of the Year” (now "Person of the Year") issue. Townes and bubble-chamber inventor Donald A. Glaser are the two surviving members of that august ensemble.

 

Townes and his wife of 69 years, Frances, have four daughters. We wish him a Happy Belated Birthday and much joy with his family.

2010-08 August, Astronomy, Astrophysics, Lasers, Optics history , , , ,

CLEO: A Three-Dimensional Gallery of Laser History

21. May 2010

By Patricia Daukantas

One of the highlights of the CLEO exhibit hall has been the extraordinary display of vintage lasers from all stages of the 50-year history of the technology. This exhibit has been on display earlier this year, but we still have been pleased to see it at CLEO 2010.

One of the biggest contributors to the laser-history exhibit was Robert Alan Hess, a holography consultant who is also a huge old-tech-gear buff. He told me that he acquired many of the vintage lasers through online auctions, company selloffs, and simple word-of-mouth. For a small bit of cash, more than one aging scientist in the process of home decluttering has been happy to part with an old instrument that’s been gathering dust for many years.

Of course, other people and organizations who have played important roles in laser history also lent their items to the exhibit. For example, here is a replica of Theodore Maiman’s first working ruby laser in front of his lab notebook from May 1960. Both items are on loan from his widow, Kathleen Maiman.

 

Here is one of the early commercial CO2 lasers from Coherent Radiation Laboratories. Under the company’s logo, somebody once attached a red label: “Gift to Schawlow Lab.”

 

In honor of today’s 30th birthday of the Pac-Man video game, here’s another blast from the past. On the top shelf of this display case are two laser pointers from the 1980s. They were considered “portable” because they were battery-powered and had a power switch on the side of the housing. Imagine wielding this during your next talk? These pointers must have had the heft and feel of “Star Wars” light sabers (or at least the things that the live actors used for their light-saber fights before the CGI people added in the “beams”).

 

Several times during CLEO Expo, Hess demonstrated a working flashlamp-pumped ruby laser that’s not much different from Maiman’s pioneering device. The ruby laser Hess was using is a commercial model that Hughes Research Laboratories—Maiman’s employer—put on the market in April 1962. Only about 100 of these lasers were manufactured and sold before technology raced ahead of the model.

Hess said his Hughes ruby laser was sold sometime in the early 1960s to Texas Instruments, which used it for sensor experiments, then declared it surplus around 1972. A man bought it and kept it, for whatever reason, until 2006, when he sold it to a laser show artist. That guy, in turn, soon put it up for auction on eBay and Hess got it.

In the photo below, Hess is using a modern He-Ne laser, hidden under the black cover, to align the optical path of the 1962 ruby laser. He will attempt to use the ruby laser pulse to punch a hole in a vintage razor blade that he found in his parents’ medicine cabinet.

 

Sure enough, the ruby laser punched a 120-m m-wide hole in the razor blade!

 

The vintage laser contained a pink ruby rod about 1.5 inches long and 3/8 inch wide, surrounded by the original helical xenon flashlamp and a diffuse white reflector. Hess isn’t sure how much life is left in the old flashlamp, but it worked every time during CLEO.

The laser history exhibit had a lot of other cool items: the first supermarket laser scanner, diode and DPSS lasers, and slabs of glass made especially for the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. I’m hoping that we at OPN will be able to put together an online gallery of all these photos I’ve taken during my week at CLEO.

I hope all our CLEO/QELS attendees have a safe journey home, and we’ll see you all next year in Baltimore, Maryland!

 

2010-05 May, CLEO/QELS, Lasers, Lasers, CLEO, Optics history , , , , , , ,

OFC/NFOEC Tribute to Charles Kao

25. March 2010

Contributed by C. David Chaffee, Chaffee Fiber Optics

 

The fiber optics community honored its own leader last night with a special two-hour tribute to Charles Kao, considered the founder of fiber optics. This was the first time the entire community has met at its most popular conference following Charlie's elevation to Nobel laureate.

 

It was in 1966 when Charlie wrote his famous paper with George Hockham suggesting that commerciable levels of photons could transmit voice and data using laser beams over "a glassy" conduit.

 

Incredibly, the paper's thesis played out. Only four years later, the famous team from Corning made the first optical fibers that met the 20 db/km spec mentioned in the Kao paper as suggesting a potentially commerciable product. This immediately put flesh on the bones of the paper, gave it credibility. There was a path where remaining steps could be played out.

 

The celebration last night included various aspects of the technology's playing out, including the Corning effort. William Shaver brought the news from the U.K.'s Ministry of Defence in May 1966 that the potential of optical fiber could lead to commercial applications. Corning's Bill Armistead named Robert Maurer to lead a small team. Don Keck and Peter Schultz joined soon thereafter. But glass losses were in the thousands of decibels per kilometer. After much frustration, the team was able to make a fiber that had losses of 17 db/km, which met the standard. Keck wrote in his lab notebook: "Whoopee!"

 

Corning thereafter decided to put optical fiber into the development phase in 1971. This was followed in 1972 by a further research step forward when gernania doping was added. This led to levels of 4 db/km.

 

This led to countless depositions and lawsuits as Corning was to successfully defend its patents in the years to come.

 

Charlie's Nobel speech was repeated by his wife, Gwen, last night. Gwen also gave the speech in Sweden. Charlie, who has Alzheimer's, was at both events but did not further participate.

 

As Gwen points out, the world knew about the announcement from the Nobel Committee within minutes of its announcement thanks to the fiber optics technology that Charlie had originally founded.

 

Charlie, who was raised in Shanghai, received special treatment from his parents because two older siblings had died from an epidemic when they were 10 and 12 years of age. He moved to the U.K. for college and stayed thereafter for many years before moving back to China,.He began working at ITT and began research that was to lead to the 1966 paper. His original area of concentration was microwave.

 

Interestingly, he spent the late 1960s, after publication of the paper, selling the idea of fiber optics around the world--to Japan, Europe and the United States, according to the Nobel speech. "Nothing in our lives was planned. It has been a roller coaster," Gwen observes.

 

Charlie and Gwen lived in Roanoke, Va. for eight years beginning in 1974. He was named Executive Scientist at ITT and the family moved to Connecticut thereafter.

 

In the 1980s, Charlie's prophesy that fiber optics would change telecommunications were coming true. Those who recall expensive three minute calls can appreciate how much current calls cost. Gwen suggests that this was the result of fiber optics.

     

"Charles planted the seed, but it would never have grown without many hands doing the toil," said Gwen. "Charles thanks all those who have worked to do that. And the plant is still growing."

      

2010-03 March, Fiber optics, OFC/NFOEC, Optics history , , , , , , , ,

Team that Made First Commerical Fiber Reunited at OFC/NFOEC

24. March 2010

 

Contributed by C. David Chaffee, Chaffee Fiber Optics    

 

In a rare historical moment, Robert Maurer, Peter Schulz and Don Keck, the team that originally made the first commerciable optical fibers in the world while at Corning, have been reunited at the show this week. I was humbled to have a few moments to talk to them about their revolutionary discovery, which has created a multi-billion dollar industry and changed the face of communications.

 

It was clear that Maurer was the leader, a man who began to look into low-loss optical fibers in 1966 when the famouns Kao/Hockham paper was first published. "Things went pretty slow at first and it was clear I was going to need some help," says Maurer. "When I got these two guys to join me, things picked up."

 

Maurer and the team had no doubt what their mission was, and that telephone companies were running out of capacity. "Everybody knew there were constraints and that optical communications was a possible solution," Keck recalls.

 

Schulz, who will fully detail the discovery tomorrow night at a special event honoring Charles Kao, remembers that it was actually a visit by a Corning official to the British Ministry of Defence that made the possibility clear. "We were really told very specifically by that Ministry of Defence team to try to make single-mode fiber with about a five micron core and to have attenuations of less than 20 dBs per kilometer. So our goal was to go from that to actually succeed."

 

None of the three would say they knew they were going to succeed from the outset. "We wanted to try," recalls Maurer. "I don't think anything can be done until it is."

 

Maurer led the group, Schulz was working with materials, Keck was working with measurements. The fibers were being drawn in the development group."We were really seeing if but using fused silica and putting additives into fused silica to change the refractive index," recalls Maurer. "We were trying to see if that method could lead to an actual fiber. We had no idea whether it could or not."

 

"Together we kept going forward as we ran our experiments," recalls Schulz.

     

"We were looking for other glasses that were high in silica at that time," says Maurer.

 

"Bob always told us if we only do things like everyone else, all you can hope for is a tie," says Keck. "We were looking for a win." Therefore, the team decided to take a contrarian approach. "The contrarian approach was to put an impurity in the glass to raise the refractive index--not enough impurity to impair anythiing. Then you put the silica around it. Ultimately it came to that sort of break that led to our winning solution. But it wasn't exactly like falling off a log."

    

Not hardly. In fact the early fibers the team worked on had losses of tens of thousands of dBs, recalls Schulz, "higher than the best conventional optical glasses. We worked away at it, picked away at it, and found what the mechanisms were and slowly but surely eliminated the losses until finally after four years of work we ended up finding what worked."

 

There were actually two eureka moments. The first involved Keck, who had just heated a fiber late in the afternoon in 1970, took the fiber out of the furnace and had a laser beam hooked up. "The laser beam hit the core of the fiber and I was blinded by the light. It was a big blaze of helium neon light and then we went through the measurements and had met our goal," recalls Keck.

 

Schulz says Eureka II came two years later when the team was struggling to bring the fiber to commercial mode. In the meantime it kept working to try to find other additives to improve it. "In 1972 we made a germania doped silica core fiber. This was multimode. This germania doped fiber we were pulling it and the light kep blazing through the fiber. First loss measurement was four dB per kilometer. We knew we had something."

 

The team stayed engaged thereafter and got support from idfferent teams and the effort got bigger until literally thousands of researchers were involved

 

While germania doping was a key, it took many, many years before the first long-haul fiber was used, Keck recalls. In fact, it was 12 years after that initial discovery."When you revolutionize the world, young scientists don't understand how long it takes."

 

Other problems were knocked out one by one through the expanded groups of researchers at Corning and elsewhere. LEDs were used before problems could be overcome with lasers, including coupling. Corning joined with Siemens to create a cable company known as Siecor. General Cable became involved.

 

The rest, as they say, is history.

 

Maurer's advice to young scientists? "Don't be afraid. Go ahead and try it." Adds Keck: "Have a dream. Find somebody to share it with."

 

2010-03 March, Fiber optics, OFC/NFOEC, Optics history , , , , ,

OFC/NFOEC Honors Charles Kao, the Father of Fiber Optics

23. March 2010

Contributed by: C. David Chaffee, Chaffee Fiber Optics

 

The celebration began anew this morning for Charles Kao, the father of fiber optics. This is the first time OFC/NFOEC has had the opportunity to honor him since he won the 2009 Nobel prize in physics, an award he shared with two other physicists. To our industry, he is the man, the kingpin, the major domo, the chairman of the board. In short, he is all that and a bag of chips.

 

Charlie has been honored before. He was so distinguished on the 25th anniversary of the seminal paper he wrote to launch the industry "Dielectric-fibre surface waveguide for optical frequencies" in the United Kingdom in 1966. This was also an OFC, the one in Baltimore in 1991. In fairness, Charlie co-authored the paper with George Hockham. But he was always the driving force, the passionate philosopher king who was given the providential vision the rest of the world lacked.

 

OFC/NFOEC does many things well. But at the top of the list is conveying a sense history for the fiber optics industry and this strengthens the sense of overall purpose and mission. Much of that is manifested by celebrations and awards such as this. Charlie's award and recognition comes in large part because what flowed out of the paper.

 

That's because the things in the paper were on-target. Four years after he predicted a silica fiber could transmit commerciable levels of light with acceptable loss (below 20 decibels per kilometer), Corning made it happen through an extraordinary effort. The accompanying lasers and detectors also were fashioned to make it work.

 

While humble in nature, Charlie has remained committed to fiber optics. This came through in the times I had the opportunity to interview him, also at OFCs. Once in the early 1980s, I asked him if fiber optics would ever be used for undersea transmission. "The oceans will be littered with fiber," he responded. This was six years before TAT-8, the first trans-oceanic fiber network was to be commissioned.

 

Charlie also predicted that people would use all the broadband that they could get their hands on, and that the costs would come crashing down. This was before we had dial-up service. And more than a few scientists have speculated that it is more than coincidence that Charlie's decision to settle in China some years ago and the rise of Huawei as a major fiber optics powerhouse.

 

In honoring Charlie this morning, Bell Labs pioneer Tingye Li recall a quote in 2004 that Charlie had made: "If you ask me how long we will see fibers being used, it may be 1,000 years without a replacement."

 

That's quite a legacy.

 

 

 

2010-03 March, Fiber optics, Information technology, OFC/NFOEC, Optics history , , , , , , , ,

Highlighting a Historical Experiment in Diffraction

18. March 2010

By Patricia Daukantas

 

Three physicists have figured out how to recreate a famous X-ray-diffraction experiment with a laser and other simple equipment. Their goal is to enable undergraduate students to follow in the footsteps of a chemical physicist who helped to decode the structure of DNA.

 

Rosalind Franklin (1920-1958), a young British scientist, took the famous X-ray diffraction image that was critical to identifying the structure of DNA as a double helix. Heidrun Schmitzer, Dennis Tierney and Gregory Braun of Xavier University (Cincinnati, Ohio, U.S.A.) include Franklin in their undergraduate course for non-majors on “Women Who Shaped Physics.” Featured scientists in the course include Marie Curie, Lise Meitner, Jocelyn Bell Burnell and Maria Goeppert-Mayer.

 

In their poster paper at this week’s American Physical Society March meeting in Portland, Ore. (U.S.A.), Schmitzer and her colleagues described the classroom experiment, which requires only simple tools: a red laser and the spring from a retractable ballpoint pen. Shining the laser beam through the spring projects a diffraction pattern strikingly similar to Franklin’s famous image. See the Xavier group’s photo of diffracted light and compare it to the X-ray image from 57 years ago (and an accompanying mathematical analysis).

 

By comparing the geometry of the pen spring to the diffraction pattern of the light, and then studying the Franklin X-ray image at its original size, the students “can determine the angle, pitch and radius of the DNA molecule, just like Rosalind Franklin,” Schmitzer wrote in the abstract.

 

Last night I did a quick trial of this with a spring from an old pen, my cats’ favorite laser pointer and a darkened room. Unlike Schmitzer, I did not block the bright center maximum with anything, so my result wasn’t as visually stunning. But I could see some evidence of the “X” pattern with faint characteristic stripes. I suspect that, with a bit more equipment and refined technique, this could make a stunning classroom demonstration.

2010-03 March, Biomedical optics, Optics history , , , , , , ,