Laserati

We have a new publication online now: multiwatts narrow linewidth fiber Raman amplifiers. Basically, the paper shows fiber Raman amplifier can be used to amplify narrow linewidth laser to a useful power level, while linewidth keeping narrow. This would be a surprise to most laser researchers. In this specific report, we have obtained 4.8 W, ~10MHz 1178nm laser with 27dB gain and more than 10% efficiency. The tricks and reason are explained in the paper.

A group of researchers grom US and Japan have imaged the grain boundary of Nd3+:YAG laser ceramics by confocal Raman and fluorescence spectroscopic methods, evidence of inhomogeneous Nd3+ distribution across grain boundaries was shown. Their work suggests that Nd3+ segregation takes place at grain boundaries leading to self-fluorescence quenching, and a trend of increasing spatial inhomogeneities in Nd3+ concentration when the doping levels exceeds 3 at%.

Reference:
M. O. Ramirez, J. Wisdom, H. Li, Y. L. Aung, J. Stitt, G. L. Messing, V. Dierolf, Z. Liu, A. Ikesue, R. L. Byer, and V. Gopalan, "Three-dimensional grain boundary spectroscopy in transparent high power ceramic laser materials," Opt. Express 16, 5965-5973 (2008)
http://www.opticsinfobase.org/abstract.cfm?URI=oe-16-9-5965

Physicists in the US and Australia have used the quantum nature of light to make an important step towards improving the sensitivity of kilometre-sized interferometers used to search for gravitational waves. By using light in a “squeezed state” they achieved a 44% improvement in sensitivity of a prototype gravitational-wave detector.

This figure could reach 300% in a full-scale detector and the team believes that squeezed-light sources could be tested in working detectors such as LIGO within 1-3 years. More sensitive detectors would be able to search larger volumes of the universe for sources of gravitational waves, making their detection more likely.

More at PhysicsWorld

A group of European researchers had triggered electrical activity in thunderstorms for the first time, using a terawatt femtosecond mobile laser. They did this by aiming their laser to thunderclouds. via: OSA

The intense laser pulses created plasma filaments in the atomosphere that could conduct electricity akin to Benjamin Franklin's silk kite string. No big lightning was triggered because the plasma filaments were still too short-lived.

"This was an important first step toward triggering lightning strikes with laser beams," says Jérôme Kasparian of the University of Lyon in France. "It was the first time we generated lighting precursors in a thundercloud." The next step of generating full-blown lightning strikes may come, he adds, after the team reprograms their lasers to use more sophisticated pulse sequences that will make longer-lived filaments to further conduct the lightning during storms.

Triggering lightning strikes is an important tool for basic and applied research because it enables researchers to study the mechanisms underlying lightning strikes. Moreover, triggered lightning strikes will allow engineers to evaluate and test the lightning-sensitivity of airplanes and critical infrastructure such as power lines.

Silicon Raman laser was the biggest breakthrough in 2006. The Intel group has made further progress. They published their new result on cascade silicon Raman laser on Nature Photonics recently.

One of the major advantages of Raman lasers is their ability to generate coherent light in wavelength regions that are not easily accessible with other conventional types of lasers. Recently, efficient Raman lasing in silicon in the near-infrared region has been demonstrated, showing great potential for realizing low-cost, compact, room-temperature lasers in the mid-infrared region. Such lasers are highly desirable for many applications, ranging from trace-gas sensing, environmental monitoring and biomedical analysis, to industrial process control, and free-space communications. Here we report the first experimental demonstration of cascaded Raman lasing in silicon, opening the path to extending the lasing wavelength from the near- to mid-infrared region. Using a 1,550-nm pump source, we achieve stable, continuous-wave, second-order cascaded lasing at 1,848 nm with an output power exceeding 5 mW. The laser operates in single mode, and the laser linewidth is measured to be <2.5 MHz.

Link to the article.

Nine research groups have begun tackling the challenge of producing a high-power 500 nm semiconductor laser in a three-year US-based research program called VIGIL.

The teams met to initiate the program at the end of November, and they have until June 2009 to hit the first milestone and produce a workable green laser based on GaN.

VIGIL stands for Visible InGaN Injection Lasers, a name that reflects the need to include high proportions of indium to obtain green light from GaN-based laser diodes. More at Optics.org

This paper is out in time, when laser TV is hot.

Speckle suppression in scanning laser display, Victor Yurlov, Anatoly Lapchuk, Sangkyeong Yun, Jonghyeong Song, and Haengseok Yang, Applied Optics, Vol. 47, Issue 2, pp. 179-187.

Abstract
The theory of speckle noise in a scanning beam is presented. The general formulas for the calculation of speckle contrast, which apply to any scanning display, are obtained. It is shown that the main requirement for successful speckle suppression in a scanning display is a narrow autocorrelation peak and low sidelobe level in the autocorrelation function of the complex amplitude distribution across a scanning light beam. The simple formulas for speckle contrast for a beam with a narrow autocorrelation function peak were obtained. It was shown that application of a diffractive optical element (DOE) with a Barker code phase shape could use only natural display scanning motion for speckle suppression. DOE with a Barker code phase shape has a small size and may be deposited on the light modulator inside the depth of the focus of the reflected beam area, and therefore, it does not need an additional image plane and complicated relay optics.

January 2008 issue of Nature Photonics has a technology focus on fiber lasers. Some recent research highlights are presented, like report of millijoule femtosecond fiber laser from Jena University. Several people from companies (SPI Lasers, IPG Photonics, Koheras) are invited to write their perspective on fiber lasers. Prof. Andreas Tuennermann, head of the Fraunhofer Insititute for Applied Optics and Precision Engineering in Jena, Germany, is interviewed on developments of fiber laser and his views on its future.

Among all the highlights, I think ultrashort pulse fiber laser is the center of spotlight. It seems suddenly, lot of companies emerge competing on femtosecond fiber lasers. Just point a few of them: IMRA, MenloSystem, Koheras, Toptica, Fianium, and FEMTO Lasers, etc.

Following is the Editorial of this Technology Focus:

Market-analyst company Strategies Unlimited believes that the fibre laser “represents the most important new technology in the laser industry in a decade,” and it’s easy to understand why.

The fibre laser is unlike any other laser on the market. Its unique geometry means it is extremely versatile, giving it applications ranging from ophthalmology to welding cars. In this month’s Technology Focus, industry experts look at using fibre lasers for marking, industrial applications and metrology.

Although these articles show that the fibre laser is already being used in commercial applications, there is still much to learn about this fascinating technology and new applications are emerging all the time. Researchers are constantly pushing the parameters to get more out of the fibre laser. Pulses are becoming shorter, pulse energies higher and power scaling is reaching unprecedented levels.

And because of these interesting advances, business is booming and fibre-laser companies are among the fastest growing firms in the laser market.

That said, Andreas Tünnermann, director of the Fraunhofer Institute for Applied Optics and Precision Engineering, believes there are still many challenges ahead. In his opinion, if industry is going to fully exploit the high-power capabilities of the fibre laser then a challenge for industry is the development of a suitable passive beam-delivery system. However, given the pace of the innovation and improvements in performance it is probable that fibre-laser technology will succeed in rising to the challenges ahead.

Photonic Lattice Inc, a startup company in Japan specializing in the design and fabrication of specialized photonic crystal elements, is happy to announce a product range of 5 optical elements for polarization control. The elements are for use with Nd:YAG lasers at 1064nm, and make it possible to produce radially and azimuthally polarized beams. Such beams have been shown to be better suited to microvia creation than either linear or circular polarizations. Additionally radial and azimuthal polarization are finding application in areas including lithography, data recording/retrieval and optical trapping.

The product range of 5 elements consists of a segmented wave plate capable of producing either radially or azimuthally polarized output, and output couplers and polarizers for radial and azimuthal polarizations. Please refer to the axisymmetric elements web page for further details.

Because the elements are fabricated as photonic crystals, operating wavelengths and specifications other than those of the standard product line can be accommodated. In addition elements have a very high degree of stability, excellent aging properties, high temperature tolerance and can withstand high optical fluences. For details and other inquiries contact contact@photonic-lattice.com for further information.

Complex dynamics of femtosecond terawatt laser pulses in air - Bin Qiao, C. H. Lai, C. T. Zhou, X. T. He, and Xingang Wang
Complex dynamics of femtosecond terawatt laser pulses in air is investigated theoretically and numerically by considering both chi susceptibility and multiphoton ionization. Our investigation shows that these two high-order nonlinearities, acting as a Hamiltonian perturbation, can destroy homoclinic ... [Appl. Phys. Lett. 91, 221114 (2007)] published Fri Nov 30, 2007. [APL: Lasers, Optics, and Optoelectronics]