Literature Search II: Keep you up in Research – the Virtual Journals and RSS Feeds!

We know how to search relevant papers but science is a very fast developing field, especially the optic communities. To keep up we have to know what is published but we can´t do every week an extensive literature search. The solution is very easy but still satisfying: virtual journals and RSS feeds!

A virtual journal presents an online collection of relevant papers from different journals published during the last week or month. In physics the virtual journals by the American Institute of Physics (AIP) and the American Physical Society (APS) are very good, covering 5 topical areas:

virtual journals

For optics it is called:

virtual journal of ultrafast science

But also the ones for quantum information and nanoscale science contain a lot of optic papers:
virtual journal of quantum information
virtual journal of nanoscale science & technology
The first two mentioned are updated every month, the nanoscale science even every week! But although virtual journals present a good overview about relevant and interesting papers for the community, papers relevant to our work are perhaps (or mostly) not published there. Hence, we have to find an additional way to search relevant papers for us… and RSS feeds will help us a lot.


RSS feeds stands for “Really Simple Syndication” and are placed on many web-pages today. They provide you with the newest articles, information and news on the web-page. You only have to click on the RSS logo and then you can create a folder in the favorite of your browser. Today, more convenient is to connect them directly to your email client or reader. All advanced clients or readers support them (if you don’t have one, search for thunderbird or google reader). Really powerful are RSS feeds if you combine them with word-filters of your email client/reader program! Using the keywords of your research, your email/ reader program collects directly all relevant papers out of hundreds of papers. You don’t have to check them all personally.

Enjoy the lecture ;)!

Very Short Pulses – from Attoseconds to Yoctoseconds!

Coincidentally I noticed a headline:

“Yoctosecond Photon Pulses from Quark-Gluon Plasmas ” [1]

Like many optic scientists I am working with femtosecond laser pulses (1fs=10^-15). Many comrades in my group are dealing with attoseconds (10^-18s). They generate them in high harmonic generation processes and can push them down to around 80as [2,3]! Near to the frontier of the zeptoseconds (10^-21s) scale. In 1as light can travel a distance of 3*10^-10m, which corresponds roughly to the length of three hydrogen atoms. Today, 80as are the limit because of physical reasons in the high harmonic generation process. But new methods are in progress to reach the zeptoseconds scale. Now, a group has proposed a method how to generated yoctoseconds; 1ys is 10^-24 seconds! They describe how high-energetic photon pulses down to the yoctosecond time scale can be produced in heavy-ion collisions, particularly during the formation of a quark-gluon plasma.
How to measure (and to produce them in reality!) and to characterize these yoctosecond pulses… future will know it. However, my comrades have enough to struggle with 80as ;).

[1] Phys. Rev. Lett. 103, 152301 (2009)
[2] Science Vol. 320, 1614
[3] Attoworld

Literature Search I: How to find Information concerning your Work!

Very essentially, often underestimated, most poorly done, about what am I talking? Of course of the literature search! The literature search is a very important and powerful tool and helps you to save a lot of time and performing good experiments. Three main purposes are behind a literature search:

1. Find information concerning your experiment achieved by other groups (part I).
2. Keep you up of the progress in your research field (part II).
3. Getting new ideas :) …

In this post I write about the first part, presenting some useful webpages for literature search. The second part follows end of the week (introducing the virtual journals).

Today, nearly all scientific information are online available in the internet. But the challenge is to find it! To do so, many search pages exist which are in parallel checking different databases about your request. Probably your university or institute offers such a search machine too. In science, probably the best search page is:

web of knowledge

The page is well done, user friendly and contains a lot of background information.
Another way (which I really like) is to search directly on the journal homepage. Every (good) journal has today a (advanced) search function. In Optics, most of the relevant articles are published in the journals of the “Optical Society of America” briefly OSA. The link to the journal page is:

Opticsinfobase

You can search on all journals or on specified ones. If you have found an interesting paper, have a look at its references and citings. They are often listed with titles and links to their PDFs. I am sure it contains a lot of interesting papers for you. With time you will notice an author who have several publications on the same field. Check their group homepage! Normally, their full publications list (even PDFs) is online.
An – unusual – approach is to search publications by google. Either by google, or its version for science:

scholar.google.com

It is not as good as the other possibilities, but I had already some nice surprises with scholar google.
Another exotic way but it is worth to mention it, is the:

arxiv server

Papers can there be pre-published before they are accepted or rejected by a journal. Some communities, like the quantum information one, are nearly publishing every article on this server too.
To complete the first part, I want to draw your attention to the:

Encyclopedia of Laser Physics and Technology

It is an open-access encyclopedia with around 570 articles, and it explains the physical principles and common techniques in laser technology.
At the end, please remember that every search machine is worthless if you use the wrong keywords. But with some training you will quickly learn the suitable ones ;).

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.