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Tag: Laser

First LIBS Spectra From Mars!

Publishing a post after long long time, busy times! But couldn’t resist posting first LIBS (Laser Induced Breakdown Spectroscopy) Spectra from Mars! It is interesting to see Hydrogen lines at 656 nm (possibly from ice on Mars or water condensation from Mars atmosphere). Carbon line adjacent to it is doubtful and needs further analysis. I can try to write more details about it later when I get time. If anyone is interested how LIBS plasma looks in Mars environment as compared to earth, you can see it here.

Leave a Comment August 24, 2012

‘Living Laser’ Created Using Jellyfish Protein And Human Cell

In a new study published today in Nature Photonics, scientists from Wellman Center for Photomedicine and Harvard Medical school have developed a “living laser” by using biological materials- human cell and jellyfish fluorescent protein. In order to get coherent beam of light from a lasing device, three things are required- a pump source (typically flash lamp,  electric current or other laser source), a ‘gain media’ for amplifying the source (optical gain) and an ‘optical cavity’ for concentration and alignment of the laser beam. Typically, crystals, dyes, gas mixtures and even alcohol have been used as gain media to amplify the light. Pumping source produces population inversion in the gain media  wherein majority of the atoms and molecules are in excited state. When a photon of appropriate wavelength interacts with such a system of atoms/molecules, stimulated emission occurs. In a very novel approach, researcher Malte Gather has used Green Fluorescent Protein (GFP) and inserted the protein in living human embryonic kidney cell. Bioluminiscent GFP was  first isolated from jellyfish in 1962 which ultimately resulted in Noble prizes for it’s discoverers. The kidney cell-GFP combo (gain medium) was then  kept in between an optical cavity made of mirrors kept 20 microns apart. The dimension of single cell gain media was also about the same. When researchers hit the cell with low energy pulses of blue light using a microscope, typical diffused ordinary fluorescence was observed. But after reaching a certain threshold of input energy (~0.9 nJ), the light output from the cell changed drastically and resulted in bright, directional and narrowband emission of green light, which are the characteristics of a laser beam. Certain regions of cell showed intense lasing action (as shown in picture above) which occurred at different but close range of wavelengths (~514-519 nm). Researchers also reported that even after prolonged lasing action, the cell was still alive. The lasing action lasted for few nanonseconds and was easily detectable. The cell was able to lase about 100 pulses at excitation pulse energy of 50 nJ after which photobleaching occurred and depleted the GFP. But an interesting aspect of GFP infused cell is that the cell is able to heal itself and replenish GFP with time.

Here is an output emission spectra of the laser filled with purified GFP solution when pumped using different wavelengths of light. As can be seen that the output spectra is independent of the pump wavelength. This spectra tells two things i) independence of excitation wavelength on the emission rules out any stimulated scattering process as an explanation for lasing action by GFP, ii) FWHM ( Full Width at Half Maximum) of about 12 nm signifies the presence of  simultaneous oscillations of various longitudinal modes.

Next figure shows that replacing the GFP solution with GFP-transfused cell resulted in much narrow output spectra. At energy threshold of 0.9 nJ, single emission peak was observed at 516 nm (FWHM <0.04 nm). As the energy was increased, multiple emission peaks were observed which can be attributed to multiple longitudinal oscillation modes. The spectral spacing between these emission line was in the range of 5 nm.

Researchers speculate that the resulting light could be used to study various intercellular processes. Before producing output light, the light travels several times through the cell placed inside the optical cavity and the resulting lasing light should contain information regarding the intercellular processes. Another possible use could be to produce such lasing beams inside the body itself to kill certain cancerous cells .

Creators of living laser, Yun and Gather,  have some broad and speculative ideas about how the technology might be used.

They suggest that biologists could turn cells of interest into lasers to study them. The light produced has a unique emission spectrum related to both the structure of the cell and the proteins inside it. “By analysing the pattern you can get some idea of what is happening inside the cell,” says Yun.

The researchers also suggest possible medical applications. Doctors today shine lasers into the body to gather images or to treat disease by attacking cells. Yun thinks that lasers could instead be generated or amplified inside the body, where they could penetrate the relevant tissues more deeply. [Nature News]

Image credit: 1) Malte Gather | Nature Photonics | Wired 2) From the supplement files of the article provided on Nature website 3) Snapshot of the plots as seen at Nature website

Reference: Single-cell biological lasers: Nature PhotonicsYear (2011) DOI: 10.1038/nphoton.2011.99

Leave a Comment June 13, 2011

LIBS Focal Point Article

If you work in the field of Laser-induced Breakdown Spectroscopy (LIBS) or plan to work in future, you have to read the latest focal point article in Applied Spectroscopy by two experts in the field, David Hahn and Nicolo Omenetto from University of Florida. It’s an excellent article (32 pages, 280 references) which reviews various fundamental studies in LIBS until now and questions certain fundamental issues (Local Thermodynamic Equilibrium assumption, spatial homogeneity of the plasma etc) which need to be clearly understood and resolved by the LIBS community in order to make LIBS a well established analytical technique. This is first in series of 2-set focal point articles on LIBS. I am in the process of reading the article and will update my blog once I have finished reading the article. You can access the full article here. It was decided by Society for Applied Spectroscopy during the FACSS 2010 meeting that all the focal point articles in Applied Spectroscopy will be available for free to all the readers. All the focal point articles since 1994 will be soon available on the SAS and ingentaconnect website pretty soon. The abstract of the LIBS article is as follows:

Laser-Induced Breakdown Spectroscopy (LIBS), Part I: Review of Basic Diagnostics and Plasma-Particle Interactions: Still-Challenging Issues Within the Analytical Plasma Community

Authors: Hahn, David W.; Omenetto, Nicoló

Source: Applied Spectroscopy, Volume 64, Issue 12, Pages 318A-366A and 1311-1452 (December 2010) , pp. 335A-366A(32)

DOI: 10.1366/000370210793561691

Abstract:

Laser-induced breakdown spectroscopy (LIBS) has become a very popular analytical method in the last decade in view of some of its unique features such as applicability to any type of sample, practically no sample preparation, remote sensing capability, and speed of analysis. The technique has a remarkably wide applicability in many fields, and the number of applications is still growing. From an analytical point of view, the quantitative aspects of LIBS may be considered its Achilles’ heel, first due to the complex nature of the laser-sample interaction processes, which depend upon both the laser characteristics and the sample material properties, and second due to the plasma-particle interaction processes, which are space and time dependent. Together, these may cause undesirable matrix effects. Ways of alleviating these problems rely upon the description of the plasma excitation-ionization processes through the use of classical equilibrium relations and therefore on the assumption that the laser-induced plasma is in local thermodynamic equilibrium (LTE). Even in this case, the transient nature of the plasma and its spatial inhomogeneity need to be considered and overcome in order to justify the theoretical assumptions made. This first article focuses on the basic diagnostics aspects and presents a review of the past and recent LIBS literature pertinent to this topic. Previous research on non-laser-based plasma literature, and the resulting knowledge, is also emphasized. The aim is, on one hand, to make the readers aware of such knowledge and on the other hand to trigger the interest of the LIBS community, as well as the larger analytical plasma community, in attempting some diagnostic approaches that have not yet been fully exploited in LIBS.
Image Credit: Applied Spectroscopy, Ingenta Connect, Authors of the article

Abstract:

Laser-induced breakdown spectroscopy (LIBS) has become a very popular analytical method in the last decade in view of some of its unique features such as applicability to any type of sample, practically no sample preparation, remote sensing capability, and speed of analysis. The technique has a remarkably wide applicability in many fields, and the number of applications is still growing. From an analytical point of view, the quantitative aspects of LIBS may be considered its Achilles’ heel, first due to the complex nature of the laser-sample interaction processes, which depend upon both the laser characteristics and the sample material properties, and second due to the plasma-particle interaction processes, which are space and time dependent. Together, these may cause undesirable matrix effects. Ways of alleviating these problems rely upon the description of the plasma excitation-ionization processes through the use of classical equilibrium relations and therefore on the assumption that the laser-induced plasma is in local thermodynamic equilibrium (LTE). Even in this case, the transient nature of the plasma and its spatial inhomogeneity need to be considered and overcome in order to justify the theoretical assumptions made. This first article focuses on the basic diagnostics aspects and presents a review of the past and recent LIBS literature pertinent to this topic. Previous research on non-laser-based plasma literature, and the resulting knowledge, is also emphasized. The aim is, on one hand, to make the readers aware of such knowledge and on the other hand to trigger the interest of the LIBS community, as well as the larger analytical plasma community, in attempting some diagnostic approaches that have not yet been fully exploited in LIBS.

Leave a Comment December 11, 2010

29th Annual AAAR Conference, Portland

I will be traveling to Portland, Oregon all of next week for attending American Association for Aerosol Research Conference. This will be my first time attending this conference and as I am relatively new to the aerosol community, this will be a great opportunity for me to learn some new stuff in aerosol characterization and measurement methods. I will also be presenting my work on elemental characterization of fine and ultra-fine aerosols using Laser-induced Breakdown spectroscopy. If you are interested, here are the abstracts of my oral presentation and poster presentation. (shameless self promotion :))

Leave a Comment October 21, 2010

Picture of The Day: Shooting Down Milky Way?

You need not worry, nobody is shooting down our galaxy. Astronomers at Very Large Telescope (VLT), Chile are simply focusing a high energy laser beam towards galactic center for observations and measurements. Taking images using ground based telescopes can be tricky as atmospheric distortions can blur the images and fine details can be lost. In order to overcome such distortions, astronomers use adaptive optics where the mirror can slightly deform in real time in response to atmospheric distortions and thus avoid blurring. For adaptive optics to work, a reference star is required which can be used for measuring the distortions caused by local atmosphere which in turn can be used to modify mirror. But suitable stars are not available everywhere in the sky, so astronomers create an artificial star using a high energy laser. The laser shown above is tuned to energize sodium atoms which are found in upper atmosphere courtesy meteorites. Laser excites sodium atoms which start glowing resulting in formation of an artificial star which can be used as a reference by the adaptive optics for clear and crisp images. Awesome, right! So that was image of the day and also my 200th post!!

Picture credit: European Southern Observatory

1 Comment October 7, 2010

Plasma-particle Interactions in Laser-induced Plasma

 Another paper came out today, well its my paper so I think I should write a little bit about it :). The study focuses on plasma-particle interactions in laser-induced plasmas. In this study, we tried to understand the fundamentals of dissociation and diffusion process in laser-induced plasmas starting from as early as 250 ns after the plasma is formed. In this study we also estimated diffusion coeffcient of Hydrogen atom. I will  write in detail later but as of now here is the abstract of the article:   

 Study of analyte dissociation and diffusion in laser-induced plasmas: implications for laser-induced breakdown spectroscopy     

Prasoon K. Diwakar, Sebastian Groh, Kay Niemax and David W. Hahn
J. Anal. At. Spectrom., 2010, Advance Article
DOI: 10.1039/C0JA00063A, Paper
   

Plasma–particle interactions are explored through the introduction of single microdroplets into laser-induced plasmas. Both spectroscopic analysis and direct imaging of analyte atomic emission are used to provide insight into the various fundamental processes, namely desolvation, atomization, and atomic diffusion. By doping the 50 µm droplets with Lu, Mg or Ca, the analyte excitation temperature and the ion-to-neutral emission ratio are explored as a function of plasma residence time following breakdown. The data suggest a change in the local plasma conditions about the analyte atoms around 15–20 µs following breakdown, which may be interpreted as an overall transition from localized (i.e. perturbed) plasma conditions to the global (i.e. bulk) plasma conditions. A direct assessment of the hydrogen atomic diffusion coefficient following analyte desolvation reveals a value of 1.7 m2 s−1 in the first 250–500 ns. This value is in good overall agreement with a theoretical analysis and with an analytical treatment of a surface source of hydrogen atoms. In contrast, calcium emission is only observed beyond about 1 µs, with a diffusion coefficient at least an order of magnitude below the hydrogen value. The temporal H and Ca emission data suggest that water vaporizes first, leaving an ever increasing Ca analyte concentration until finally, with nearly all water desorbed, the Ca fraction is vaporized. Overall, the data support the conclusion that finite time-scales of heat and mass transfer play an important role in localized plasma perturbations in the vicinity of the analyte, which has important implications for the LIBS analyte signal.   

Leave a Comment September 29, 2010

Hawking Radiation Observed

In a very recent study, researchers from Italy have claimed to observe the elusive  Hawking radiations by creating a miniature analog of black hole in the lab. The study which is going to be published in Physical Review Letters would be the first study to observe it after theoretical details were first presented by Stephen Hawkings in 1974.  He predicted that instead of taking in everything, blackholes can also emit thermal radiations. Many have tried to observe the phenomena but have failed so far. This results of this study will be scrutinized and debated in the scientific community in coming days. The experimental set up consisted of high energy ultrashort laser pulses which was focused onto a fused silica glass to create gravitational analogue of black holes.

Article:  Hawking radiation from ultrashort laser pulse filaments, Belgiorno et. al. arXiv:1009.4634v1 [gr-qc]

Picture credit: Wikimedia Commons | Used under creative commons license

Leave a Comment September 29, 2010

Photoemission Delay Time

Photoelectric effect has been known to us for a long time. Heinrich Hertz first observed this phenomena in 1887 where a material absorbs electromagnetic radiation and emits electrons. While most of details are clearly understood, one aspect which has been missing is the delay time in emission of electrons after the matter absorbs photon. If delay exists, does the delay also depend on the energy level from which electron is being emitted? Until now, it was assumed that the photo-emission process is instantaneous. Recent study by researchers at Max Planck Institute of Quantum Optics in Munich, Germany and group of other collaborators , has been able to precisely measure the delay time in photoemission process using ultra-short time measurement technology. They used Neon atoms to study the phenomena. Neon  is more complex than Helium, but it was chosen because Neon is simpler to model theoretically and it also has higher photo-ionization cross-section resulting higher Signal-to-Noise ratio. They found out that that electrons leave 2P level subshell   Formula attoseconds after the electrons have left 2S subshell.  The delaytime of 21 attoseconds between electron emission from 2S and 2P seem to be very small, but it’s an important result as it shows that the process is not instantaneous, as it was assumed until now, and there is certain delay involved possibly due to electron-electron interactions. Scientists also performed complex theoretical computations to calculate the delay time and they came with a delay time 0f 5 attoseconds. The discrepancy can be attributed to multi-electron Neon atom system which makes it very difficult to make accurate theoretical computations. For experiments, two ultrafast laser pulses were used: extreme UV pulse (<200 attosecond duration) was used to eject electrons from 2S and 2P subshells while near infra-red pulse was used for time resolved measurements.

“These to-date poorly understood interactions have a fundamental influence on electron movements in tiniest dimensions, which determine the course of all biological and chemical processes, not to mention the speed of microprocessors, which lie at the heart of computers”, explains Ferenc Krausz, co-author of the study from MPQ. “Our investigations shed light on the electrons’ interactions with one another on atomic scale“. [Attoworld.de Press Release]

The results of the study was published in Science (June 2010, Vol 328, pp 1658) and abstract is as follows:

Delay in Photoemission

Schultze et al.

Vol. 328. no. 5986, pp. 1658 – 1662
DOI: 10.1126/science.1189401

Photoemission from atoms is assumed to occur instantly in response to incident radiation and provides the basis for setting the zero of time in clocking atomic-scale electron motion. We used attosecond metrology to reveal a delay of Formula attoseconds in the emission of electrons liberated from the 2p orbitals of neon atoms with respect to those released from the 2s orbital by the same 100–electron volt light pulse. Small differences in the timing of photoemission from different quantum states provide a probe for modeling many-electron dynamics. Theoretical models refined with the help of attosecond timing metrology may provide insight into electron correlations and allow the setting of the zero of time in atomic-scale chronoscopy with a precision of a few attoseconds.

Photocredit: Attoworld.de Press Release/ MPQ/ LMU/ T. Naeser/ C. Hackenberger

Leave a Comment August 23, 2010

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