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Tag: Laser

Ode To The Laser

It was in May, 50 years ago when first Laser was invented and this whole year has been dedicated to Laser with various events and conferences being organized all around the world. This Ode To Laser comes from Jorge Cham at PhdComics celebrating the occasion:


Leave a Comment August 4, 2010

Shrinking Protons

If the results of new study  holds then the size of proton is smaller than what it was thought to be or measured in earlier experiments, roughly 4% smaller. This can have serious implications on the quantum mechanic theories itself. The experiment the group of Randolf Pohl at Max Planck Institute, Munich, Germany, performed was very neat, even though the possibility of any mistake or missing out on some factor while calculating the radius of proton cannot be ruled out.

Protons along with neutrons form the nuclei of atom. While protons are very common particle and has been studied for a while, still not everything is clearly understood about them, especially the inernal structure. Protons are positively charged particles which further consists of smaller fundamental particles called quarks. The charge is roughly spread around in a spherical area and when we say the size of proton, it’s the size of this charge cloud. Proton size is extremely small, roughly 10,000 times smaller than orbit of the electrons.

So, how do we go about measuring the size of proton which is so tiny- spectroscopic measurement is the answer. Scientists can measure the size of the proton by meausring the interactions of electron with proton. According to quantum mechanics, the electrons orbitting around protons can occupy certain discrete energy levels and the size of the proton also contributes in determining these energy levels. Many such measurements have been performed to measure the size of proton, the most recent estimate being 0.8768 femtometers [Nature].

In the current sudy, researchers measured the size of protons to be 0.84184 fm which is 10 times more precise than previous estimates, but numbers don’t match. In order to do so, they created an exotic version of Hydrogen, muonic Hydrogen, which is exactly like Hydrogen with the lone electron replaced by muon. Muons have same charge as electrons but they are bout 200 times heavier than electrons, thus they orbit more close to the proton and are smaller in size and thereby interactions between them are more sensitive and pronounced and more dominated by the protons. To create muonic hydrogen, they bombarded muons at hydrogen and roughly 1% of hydrogen was converted to muonic hydrogen.

As soon as the muonic hydrogen was formed, they performed spectroscopic measurements to measure the Lamb shift  which ultimately can be used to measure the size of proton. Lamb shift is a very important phenomena in quantum mechanics. Basically, simple QED says that the 2S and 2P energy levels will have same energy, but in 1947 it was discovered by Rutherford and Lamb that it’s not so and there are energy differences between the two due to result of various interactions including the effect of proton size. In muonic hydrogen, this effect or Lamb shift is more pronounced. When laser is fired at munoic hudrogen, the electron gets excited and jump to higher energy level and thus they can measure the energy difference between the 2S and 2P levels, the Lamb shift, which ultimately can be used to estimate the size of proton.

A short time after the atoms are created, they blast in a pulse of laser light with its frequency tuned close to the frequency corresponding to the splitting between the 2S and 2P states. The 2P state has a very short lifetime, so any atoms that get excited by the laser will decay very quickly, and emit an x-ray in the process (because the energy difference between the ground state and the 2P state is enormous, thanks to the heavy muon). When the laser is tuned to exactly the right frequency, they see lots of x-rays from decaying atoms. When it’s a little bit off, the number of x-rays drops off dramatically. Then they just need to measure the laser frequency, and they get the Lamb shift directly. And with a bit of math, they can convert that to a measurement of the proton size. [Science Blogs ]

Something can be wrong in these experiments or earlier experiments including some gaps in the theory itself, so more experiments need to be carried out to clarify this discrepancy. But the experiment is very neat which I liked a lot. Hope this study and further studies will result in providing better picture of proton size and inner structure.

Reference: Pohl, R. et al. Nature 466, 213-217 (2010). | Article

Picture credit: Flickr user fatllama (picture not from this experiment) Used under creative commons license.

4 Comments July 13, 2010

Celebrating 50 Years of Lasers:The First Laser

The first laser

Article By: Charles H. Townes

Excerpt from A Century of Nature: Twenty-One Discoveries that Changed Science and the World: Editors Laura Garwin and Tim Lincoln (Reprinted under fair-use provisions of US copyright law. ©2003 by The University of Chicago Press)

When the first working laser was reported in 1960, it was described as “a solution looking for a problem.” But before long the laser’s distinctive qualities—its ability to generate an intense, very narrow beam of light of a single wavelength—were being harnessed for science, technology and medicine. Today, lasers are everywhere: from research laboratories at the cutting edge of quantum physics to medical clinics, supermarket checkouts and the telephone network.

Theodore Maiman made the first laser operate on 16 May 1960 at the Hughes Research Laboratory in California, by shining a high-power flash lamp on a ruby rod with silver-coated surfaces. He promptly submitted a short report of the work to the journal Physical Review Letters, but the editors turned it down. Some have thought this was because the Physical Review had announced that it was receiving too many papers on masers—the longer-wavelength predecessors of the laser—and had announced that any further papers would be turned down. But Simon Pasternack, who was an editor of Physical Review Letters at the time, has said that he turned down this historic paper because Maiman had just published, in June 1960, an article on the excitation of ruby with light, with an examination of the relaxation times between quantum states, and that the new work seemed to be simply more of the same. Pasternack’s reaction perhaps reflects the limited understanding at the time of the nature of lasers and their significance. Eager to get his work quickly into publication, Maiman then turned to Nature, usually even more selective than Physical Review Letters, where the paper was better received and published on 6 August.

With official publication of Maiman’s first laser under way, the Hughes Research Laboratory made the first public announcement to the news media on 7 July 1960. This created quite a stir, with front-page newspaper discussions of possible death rays, but also some skepticism among scientists, who were not yet able to see the careful and logically complete Nature paper. Another source of doubt came from the fact that Maiman did not report having seen a bright beam of light, which was the expected characteristic of a laser. I myself asked several of the Hughes group whether they had seen a bright beam, which surprisingly they had not. Maiman’s experiment was not set up to allow a simple beam to come out of it, but he analyzed the spectrum of light emitted and found a marked narrowing of the range of frequencies that it contained. This was just what had been predicted by the theoretical paper on optical masers (or lasers) by Art Schawlow and myself, and had been seen in the masers that produced the longer-wavelength microwave radiation. This evidence, presented in figure 2 of Maiman’s Nature paper, was definite proof of laser action. Shortly afterward, both in Maiman’s laboratory at Hughes and in Schawlow’s at Bell Laboratories in New Jersey, bright red spots from ruby laser beams hitting the laboratory wall were seen and admired.

Maiman’s laser had several aspects not considered in our theoretical paper, nor discussed by others before the ruby demonstration. First, Maiman used a pulsed light source, lasting only a few milliseconds, to excite (or “pump”) the ruby. The laser thus produced only a short flash of light rather than a continuous wave, but because substantial energy was released during a short time, it provided much more power than had been envisaged in most of the earlier discussions. Before long, a technique known as “Q switching” was introduced at the Hughes Laboratory, shortening the pulse of laser light still further and increasing the instantaneous power to millions of watts and beyond. Lasers now have powers as high as a million billion (10 to power 15) watts! The high intensity of pulsed laser light allowed a wide range of new types of experiment, and launched the now-burgeoning field of nonlinear optics. Nonlinear interactions between light and matter allow the frequency of light to be doubled or tripled, so for example an intense red laser can be used to produce green light.

I had a busy job in Washington at the time when various groups were trying to make the earliest lasers. But I was also supervising graduate students at Columbia University who were trying to make continuously pumped infrared lasers. Shortly after the ruby laser came out I advised them to stop this work and instead capitalize on the power of the new ruby laser to do an experiment on two-photon excitation of atoms. This was one of the early experiments in nonlinear optics, and two-photon excitation is now widely used to study atoms and molecules.

Lasers work by adding energy to atoms or molecules, so that there are more in a high-energy (“excited”) state than in some lower-energy state; this is known as a “population inversion.” When this occurs, light waves passing through the material stimulate more radiation from the excited states than they lose by absorption due to atoms or molecules in the lower state. This “stimulated emission” is the basis of masers (whose name stands for “microwave amplification by stimulated emission of radiation”) and lasers (the same, but for light instead of microwaves).

Before Maiman’s paper, ruby had been widely used for masers, which produce waves at microwave frequencies, and had also been considered for lasers producing infrared or visible light waves. But the second surprising feature of Maiman’s laser, in addition to the pulsed source, was that he was able to empty the lowest-energy (“ground”) state of ruby enough so that stimulated emission could occur from an excited to the ground state. This was unexpected. In fact, Schawlow, who had worked on ruby, had publicly commented that transitions involving the ground state of ruby would not be suitable for lasers because it would be difficult to empty adequately. He recommended a different transition in ruby, which was indeed made to work, but only after Maiman’s success. Maiman, who had been carefully studying the relaxation times of excited states of ruby, came to the conclusion that the ground state might be sufficiently emptied by a flash lamp to provide laser action—and it worked.

The ruby laser was used in many early spectacular experiments. One amusing one, in 1969, sent a light beam to the Moon, where it was reflected back from a retro-reflector placed on the Moon’s surface by astronauts in the U.S. Apollo program. The round-trip travel time of the pulse provided a measurement of the distance to the Moon. Later, ruby laser beams sent out and received by telescopes measured distances to the Moon with a precision of about three centimeters—a great use of the ruby laser’s short pulses.

When the first laser appeared, scientists and engineers were not really prepared for it. Many people said to me—partly as a joke but also as a challenge—that the laser was “a solution looking for a problem.” But by bringing together optics and electronics, lasers opened up vast new fields of science and technology. And many different laser types and applications came along quite soon. At IBM’s research laboratories in Yorktown Heights, New York, Peter Sorokin and Mirek Stevenson demonstrated two lasers that used techniques similar to Maiman’s but with calcium fluoride, instead of ruby, as the lasing substance. Following that—and still in 1960—was the very important helium-neon laser of Ali Javan, William Bennett, and Donald Herriott at Bell Laboratories. This produced continuous radiation at low power but with a very pure frequency and the narrowest possible beam. Then came semiconductor lasers, first made to operate in 1962 by Robert Hall and his associates at the General Electric laboratories in Schenectady, New York. Semiconductor lasers now involve many different materials and forms, can be quite small and inexpensive, and are by far the most common type of laser. They are used, for example, in supermarket bar-code readers, in optical-fiber communications, and in laser pointers.

By now, lasers come in countless varieties. They include the “edible” laser, made as a joke by Schawlow out of flavored gelatin (but not in fact eaten because of the dye that was used to color it), and its companion the “drinkable” laser, made of an alcoholic mixture at Eastman Kodak’s laboratories in Rochester, New York. Natural lasers have now been found in astronomical objects; for example, infrared light is amplified by carbon dioxide in the atmospheres of Mars and Venus, excited by solar radiation, and intense radiation from stars stimulates laser action in hydrogen atoms in circumstellar gas clouds. This raises the question: why weren’t lasers invented long ago, perhaps by 1930 when all the necessary physics was already understood, at least by some people? What other important phenomena are we blindly missing today?

Maiman’s paper is so short, and has so many powerful ramifications, that I believe it might be considered the most important per word of any of the wonderful papers in Nature over the past century. Lasers today produce much higher power densities than were previously possible, more precise measurements of distances, gentle ways of picking up and moving small objects such as individual microorganisms, the lowest temperatures ever achieved, new kinds of electronics and optics, and many billions of dollars worth of new industries. The U.S. National Academy of Engineering has chosen the combination of lasers and fiber optics—which has revolutionized communications—as one of the twenty most important engineering developments of the twentieth century. Personally, I am particularly pleased with lasers as invaluable medical tools (for example, in laser eye surgery), and as scientific instruments—I use them now to make observations in astronomy. And there are already at least ten Nobel Prize winners whose work was made possible by lasers.

There have been great and good developments since Ted Maiman, probably a bit desperately, mailed off a short paper on what was then a somewhat obscure subject, hoping to get it published quickly in Nature. Fortunately, Nature’s editors accepted it, and the rest is history.

Copyright notice: Excerpted from pages 107-12 of A Century of Nature: Twenty-One Discoveries that Changed Science and the World edited by Laura Garwin and Tim Lincoln, published by the University of Chicago Press. ©2003 by The University of Chicago. All rights reserved. This text may be used and shared in accordance with the fair-use provisions of U.S. copyright law, and it may be archived and redistributed in electronic form, provided that this entire notice, including copyright information, is carried and provided that the University of Chicago Press is notified and no fee is charged for access. Archiving, redistribution, or republication of this text on other terms, in any medium, requires the consent of the University of Chicago Press and of the author.

Leave a Comment May 19, 2010

LIDAR Maps Mayan City In 4 Days!

Another Laser related research update! A new modified LIDAR (Light Detection And Ranging) method (swath mapping) was used to map one of the largest cities of ancient Mayan city, Caracol, covered under thick tropical forest. The same job would have taken 20-25 years of surveying by traditional ground based techniques, LIDAR did the job in 4 days!!

In only four days, a twin-engine aircraft equipped with an advanced version of lidar (light detection and ranging) flew back and forth over the jungle and collected data surpassing the results of two and a half decades of on-the-ground mapping, the archaeologists said. After three weeks of laboratory processing, the almost 10 hours of laser measurements showed topographic detail over an area of 80 square miles, notably settlement patterns of grand architecture and modest house mounds, roadways and agricultural terraces. [NY Times]

The NASA technology aboard the Cessna saw beyond the rainforest and detected thousands of new structures, 11 new causeways, tens of thousands of agricultural terraces and many hidden caves – results beyond anyone’s imagination. The data also confirm the size of the city (spread over 177 square kilometers or 68 square miles) and corroborate the Chases’ previous estimates for the size of the population (at least 115,000 people in A.D. 650).[UCF Newsroom]

“It’s very exciting,” said Arlen Chase. “The images not only reveal topography and built features, but also demonstrate the integration of residential groups, monumental architecture, roadways and agricultural terraces, vividly illustrating a complete communication, transportation and subsistence system.”[UCF Newsroom]

You can read the full story at New York Times. The research is collaboration between University of Central Florida, NASA and University of Florida. My friend, Pravesh, works in Univ of Florida LIDAR lab and probably she will be able to provide more input about these results.

Source: NY Times, UCF Newsroom, Flickr: AJ Baxter

Leave a Comment May 12, 2010

Zapping Malaria: One Mosquito At A Time

Intellectual Ventures have come up with a very novel approach of controlling Malaria, using a laser to target the mosquito, figure out if its male or female and then zap it. Sounds like some kind of video game, right, but this technique has been tested in labs and even works. Intellectual Ventures Lab calls this invention as Photonic Fence which detects the mosquito flying at a distance using a low powered laser. This laser doesn’t kill but it identifies whether it’s malaria causing female mosquito or other harmless insect by measuring the size and frequency of the wing-beats of the insect. Female mosquito has lower frequency of wing-beats as compared to their male counterparts and they are larger in size. Once the malaria causing mosquito is identified, another ‘lethal’ laser is targeted at the mosquito finally zapping it either by destroying it’s DNA or by thermal energy. The laser energy and frequency they use is harmless to human  tissue.

Additionally, the company has found applied some very interesting optical and magnetic properties of crystal called hemozoin ,which is also called the malaria pigment, to detect malaria infection. The original discovery about optical properties of hemezoin for detection of Malaria was done in a study  by a group at McGill Univeristy in 2008. When a person is infected with malaria, the parasite enters the red blood cells and feed on hemoglobin but they are unable to digest the heme or the iron containing part of the hemoglobin and sequesters it in form of hemozoin. Presence of hemozoin in blood is indication of malaria infection. It has been found out by researchers at McGill University and confirmed by intellectual ventures that hemozoin interacts with high energy femtosecond laser and it emits distinctive wavelength of light which can be used for non-invasive diagnostics of  malaria. They also found out that the hemozoin is slightly magnetic in nature. These newly found optical and magnetic properties can be used for manipulating the hemozion and ultimately destroy the parasite.

We are attempting to find ways to use this approach to treat malaria as well as to detect it. By tuning the light used in the laser beam to just the right wavelength, we hope to induce the hemozoin to emit optical pulses that actually destroy the parasite’s DNA without harming the surrounding human tissue.Besides being optically active, hemozoin is very slightly magnetic. That opens another avenue for attacking the parasite. We’ve invented ways to magnetically shake or spin hemozoin crystals, rupturing the parasite’s innards enough to kill it. [Intellectual Ventures]

Here are some SEM images of hemozoin nanocrystal:

Also, you can listen to Nathan Myhrvold, co-founder of Intellectual Ventures,  talking about this invention in his recent TED talk.

Source and Photo: Intellectual Ventures Lab

Reference article on hemezoins: doi: 10.1529/biophysj.107.125443

2 Comments May 11, 2010

Laser Induced Healing

The title might be little deceptive, but maybe not. These days lasers can be seen in use everywhere, some examples being: laser pointers, laser shows, analyzing aerosols, eye treatments, inducing rains, cooling down the atoms and so on. If lasers can do everything, they can also stitch your wounds as well, right, without leaving any scars, no pain, no damage to surrounding tissues. Sounds excellent. Well, scientists have been working on a technique called Photochemical Tissue Bonding (PTB) where they use a photo-reactive dye which is applied to the tissue surface and then it’s illuminated with a laser for few minutes. The dye absorbs the laser energy, the energy is not very high to cause any thermal damage to the tissue, and it induces collagen molecules in the tissue to cross-link by formation of reactive intermediates. The dye which has been typically studied and used for this process is Rose Bengal which is a FDA approved dye and has been extensively used for liver treatments and also being studied for liver and eye cancer studies. Rose Bengal absorbs the light strongly around 530-550 nm (maximum at 550 nm) and hence a visible 532 nm laser can be used to induce the bonding process. The mechanism of bonding is not still understood clearly and that provides a good opportunity to study the process and optimize the process so that it can be applied for healing people.

Photo Credit: KOCHEVAR LAB At Wellman center

References: Microvascular anastomosis using a photochemical tissue bonding technique: Lasers in Surgery and Medicine  Volume 39 Issue 9, Pages 716 – 722
Electron Transfer Quenching of the Rose Bengal Triplet State: Photochemistry and Photobiology, 1997, 66(1): 15-25

Leave a Comment May 5, 2010

The Rain Maker: Laser-induced Water Condensation

No, I am not talking about John Grisham novel, rather I am talking about a new study published today in Nature Photonics which uses laser energy to induce rain! Researchers at Freie Universität Berlin, Université de Genève and CNRS France have developed a technique called Laser-induced Water Condensation where they use a high energy pulsed femtosecond laser to form a guided filament which can be used to induce water-cloud condensation in free sub-saturated atmosphere . They conducted laboratory as well as field experiments to test the technique and the researchers are very optimistic that with further optimization of various parameters, it can be used to seed the clouds and form rain in parched dryer parts of the world without any danger of any side effects to the environment. Usually, conventional techniques for seeding the cloud include adding silver iodide molecules to upper atmosphere or sodium, potassium, lithium based salts in lower atmosphere to induce cloud condensation. But theses techniques have issues due to side-effects it can cause to the environment. This new technique described in the current study has no such side effects. The pulsed femtosecond laser can form a long filament shaped plasma by altering the refractive index of the air and self focusing nature of such laser beams. These plasma filaments when interact with air molecules ionize the Nitrogen and Oxygen molecule and provide the seeding material for condensation process. In their lab experiments , the researchers were able to increase the volume of condensed water droplets by 50% by laser-induced process. You can see in the video here showing the effect of plasma filament on the number and size of condensed particles in the saturated chamber (230% saturation). The flashes you see are the result of increase in the scattering of probe laser due to increased size and number concentration of water droplets in the chamber due to laser-induced water condensation process.

Even though the researchers feel that with proper optimization and further study, this method can be used in real world, but  some researchers are not too optimistic about it due to certain issues. The major issue being the relative humidity condition, the lab experiments were performed at relative humidity of about 230% which is never the case in atmosphere ( maximum ~ 101 %). So, the lab results can not be expected to be achieved in the atmospheric conditions. To counter that, the researchers in current study also performed experiments in open atmosphere in Berlin and LIDAR data showed the enhancement in condensation process using laser. Another issue can be the laser span, in order to increase the laser-induced effect to larger volumes of the cloud, an effective laser spanning technique will be needed. Nonetheless, it’s an interesting study, atleast from the proof of concept point of view.
Source: Nature Photonics : 2 May 2010 | doi:10.1038/nphoton.2010.115

Picture Credit: Jean-Pierre Wolf/University of Geneva  and New Scientist

1 Comment May 3, 2010

Laser Pioneers- A Pictorial Journey

Lasers celebrate 50 years of it’s existence this year. It’s been a remarkable journey and lasers now are an important tool in making fundamental discoveries besides being part of our day to day lives. In my previous post about lasers I wrote about some very important discoveries and inventions related with lasers which ultimately led to scientists winning Nobel Prizes. Here I am providing a link for a pictorial view of all the Laser pioneers who made possible the curent extensive use of lasers in research as well as in our daily lives. The picture shown here is of Theodore Maiman who is credited with the invention of first laser (Ruby Laser) in 1960, even though several other researchers and groups led to the development of the laser science simultaneously.

“… Solve a puzzle, understand something new, and it’s exhilarating …” — Charles Townes, Nobel Laureate in the field of Lasers and Masers.

Sources: Spie.org   Photo: Theodore Maiman: Laser Inventor- Spie.org

Leave a Comment April 8, 2010

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