Optics at the disco

Thinking about going out tonight...?

If so, you might be familiarized with the lights shown in the video.

Sometimes people seem to dance in slow motion, as in the minute 1'02 of the video; the lights responsible of this effect are called stroboscopic lights.

Smoke is also widely used at the disco to produce optical effects: light is slightly dispersed by it and coloured ray traces are easily observed (example: minute 1'14 of the video).

And do you like drinking tonic? If you ask for one at the disco, it can have this appereance:

Don't worry! You haven't asked for the wrong drink and neither have you become colour-blind... It happens because in some discos there are ultraviolet lights (emitting at around 365nm) which excites quinine, a substance contained in the tonic, and producing fluorescence.

Acknowledgments: the author would like to thank B. Hester (from University of Maryland Student Chapter) for her help with the tonic fluorescence.

Where is your Coffee Cup?

…because soon we have coffee break! And you don’t want to miss it this time…



If you have heard something about the taste, please make a comment ;). It seems that they enjoy their coffees and tea.

To heat the water they used a continuous wave Nd:YAG laser with a maximum power of 2.5kW at 1064nm. The wavelength is already in the near infrared range and therefore not visible to our eyes. This type of laser is very often used in industry for material processing. Unfortunately, I couldn’t find more information about this group, what they are mainly working. Looking around in their laboratory I guess it is not an optics group but probably an engineering group – working somehow on material processing.
Have you already asked yourself, why we see the laser beam even it should be invisible for our eyes? The reason is simple. The digital camera with the CCD sensor (Nobel Prize this year!) is sensitive at these wavelengths too. Normally, the camera blocks the near infrared and infrared spectral range by a filter. If you watch carefully the movie, you will notice that they change the camera to their research camera where they do not have such a filter (after 42 seconds). Hence, the laser light scattered by the water can be detected by this camera and we can see the laser light on the camera screen.

Photonic Crystal Fibers: the 2. Generation of Optical Fibers

(taken from Optics Express Vol. 15, pp 15365)


Charles K. Kao was awarded this year with the Nobel Prize for his fundamental contribution about optical fiber in 1966. Nowadays, applied in high speed data communication optical fibers have an enormous impact in public life. But, is this already everything from optical fibers? Definitely not! In 1996 the research group around Prof. Dr. Russell was able to create the first micro-structured optical fibers, later called photonic crystal fibers (PCF). Contrary to normal optical fibers which consist of a core surrounded by a cladding with a smaller refractive index for total internal reflection, a PCF doesn’t have a cladding in this sense but its core is periodically surrounded by several small “air tunnels” which acts like a cladding, and much more! This construction allows researcher to engineer different parameters of the fiber, like the zero dispersion wavelength (ZDW) and the single mode condition. In bulk silica the ZDW is approximately 1.3µm. Above 1.3µm the dispersion is positive and this wavelength regime is called anomalous regime because it allows new phenomena (solitons, supercontinuum) which are not possible in the normal dispersion regime (negative dispersion). Note, that the dispersion parameter D [ps/km*nm] is proportional to –B2, the group velocity dispersion. The design of photonic crystal fibers enables to shift down the ZDW to 600nm, thus in the working regime of Ti:Sa lasers (800nm). Doing so, solitons (= “self-guiding light bullets”) are created which cover together a very large spectral range, called supercontinuum. Often, the supercontinuum ranges from 530-1100nm but depending on the fiber material, design, length and input laser parameter, different spectral ranges can be covered. Right now, to my knowledge the record covers a wavelength range from 1-5µm using an 8mm telluride PCF.
During the last years supercontinuum spectrums have found applications in spectroscopy. But the most famous, and perhaps most important one, application is on the field of laser based precision spectroscopy, for precision measurements of atomic structures and optical frequencies. Thereby the optical frequency comb technique is applied, which is based too on fiber generated supercontinuum. In 2005, Theodor Hänsch (Max Planck Institute of Quantum Optics) was one of the Nobel Prize winners “for their development of laser based precision spectroscopy, that is, the determination of the colour of the light of atoms and molecules with extreme precision.” Without fiber generated supercontinuum, hence without photonic crystal fibers, these very accurate measurements wouldn’t have been possible. And public life is also profiting from these experiments, because e.g. it helps to improve GPS systems.
Today, many different kind of photonic crystal fibers exist with different properties (see picture). Some have instead of a core a whole, so called hollow core fiber, other ones are doped in the core or cladding with another material, mostly Ytterbium (Yb) or Erbium (Eb). These doped fibers are extensively used in fiber amplifiers and fiber lasers, probably the next generation of lasers.
Photonic crystal fibers are at the very beginning to enter scientific experiments in a broad application range, and because of their special properties we can expect many new techniques and exciting discoveries. Hence, it is a good time to consider PCFs in your experiment…and perhaps you may be awarded with the Nobel Prize some years later ;).

Review Articles:
Photonic Crystal-Fibers
by P. St. J. Russell
JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 24, NO. 12, DECEMBER 2006

Nonlinear Waveguides Optics and Photonic Crystal Fibers
by J. C. Knight
Optics Express Vol. 15, pp 15365

Research Groups:
Russell Group at Max Planck Institute for the Science of Light, Erlangen

Centre for Photonics & Photonics Material, University of Bath

Optoelectronics Research Centre, University of Southampton

Companies:
NKT Photonics
(former called Crystal-Fibre)
with the well-known distributors
Thorlabs and Newport

Nufern

nLIGHT
(former Liekki, acquired by nLIGHT)

Laser and armies.

While the laser is always presented as a big destructive weapon in any science fiction story, the reality is that they haven't play a role at all as weapons. They are extensively used as guidance systems, detection systems and such, but not direclty as weapons, until now.

Here is an entry from the Boing Boing blog about Boeing getting money from the US army to build big lasr that they promes can harm the enemy's army.

" The Advanced Tactical Laser (ATL) is a directed energy weapon (aka ray gun) developed by Boeing under a US military contract. According to an overview document (PDF) about Boeing's Directed Energy Systems program, "In August 2009, the ATL defeated a ground vehicle target from the air, demonstrating its first air-to-ground, high-power laser engagement of a tactically representative target." The video above documents that experiment, in which the laser weapon, mounted on a C-130H Hercules transport plane, was fired at a car. See the Boeing site for more videos, including aerial footage. (via Smithsonian Air & Space) "

More details here. And some videos here.

Nobel Prize 2009: Kao, Boyle and Smith

Nobel Prize 2009 for Charles K. Kao "for groundbreaking achievements concerning the transmission of light in fibers for optical communication" and W. S. Boyle and G. E. Smith "for the invention of an imaging semiconductor circuit – the CCD sensor".

Charles K. Kao was born 1933 in Shanghai, China. He got his Ph.D. in Electrical Engineering 1965 from Imperial College London, UK. He worked at Standard Telecommunication and Chinese University of Hong Kong. He retired in 1996.
Willard Sterling Boyle, was born 1924 in Amherst, NS, Canada. He got his Ph.D. in Physics 1950 from McGill University, QC, Canada. He was the executive Director of Communication Sciences Division, Bell Laboratories, Murray Hill, NJ, USA; he is retired since 1979.
George Elwood Smith, was born 1930 in White Plains, NY, USA. He got his Ph.D. in Physics 1959 from University of Chicago, IL, USA and also worked Bell Laboratories He got retired in 1986.

Why is their contribution so important? C. Kao has been awarded the Nobel Prize due to his prediction of the optical fiber. Thanks to his discovery, you are reading this! Optical fibers are widely used in communications; it allows information spreading almost at the speed of light.
Boyle and Smith invented the CCD (charged coupled device). Do you have a digital camera? If the answer is yes, thank Boyle and Smith! CCD sensors are sometimes called "the electronic eye". Without them, not only the digital camera would have taken a slower course, but also the images from telescopes or the way we analyze beams in optics.

To know more about their contribution to Physics (and particulary to Optics), I recommend you to download the digest with easy-reading information for the public about their work.

You can find more information about Nobel Laureates at http://nobelprize.org (you can even ask them a question!); a more detailed report (but still easy to understand) can be found here.