Nov. 1, 2001
Submissions now being accepted for the Young Investigator Award; Electron laser amplifies ultraviolet light by a factor of 10 million; Aperiodically poled lithium niobate yields active tunable frequency converter...

Submissions now being accepted for the Young Investigator Award
The International Society for Optical Engineering (SPIE) is now accepting submissions for the Young Investigator Award, which is presented annually at Photonics West (San Jose, CA). The award, given in memory of Heather Williamson Messenger, former executive editor of Laser Focus World, is for the best paper by a young researcher who has graduated within five years of the conference. The award consists of a cash prize and publication of the winning paper in Laser Focus World. To qualify for the award, the researcher must be the principal author, and should indicate his or her wish to be considered for this award when submitting an abstract. For more details at this stage, send an e-mail to Mirja Salminen at [email protected].

When submitting the final manuscript, the researcher should also submit a letter nominating his or her paper for consideration and certifying that the qualifications for the award have been met. This letter must be accompanied by a photocopy of the researcher's most recent diploma and five copies of the manuscript. These copies are in addition to the copies submitted for inclusion in the proceedings volume, and should be submitted separately. For review purposes, all materials must be received at SPIE by the manuscript due date of Dec. 17. The SPIE mailing address is P.O. Box 10, Bellingham, WA 98227-0010. The shipping address is 1000 20th Street, Bellingham, WA 98225-6705.

Electron laser amplifies ultraviolet light by a factor of 10 million
An international team of scientists at DESY (Hamburg, Germany) has built what is believed to be the world's most powerful free-electron laser (FEL) for the ultraviolet wavelengths at which it operates. The FEL produced an amplification of 10 million, which corresponds to the theoretically expected peak performance for such a device, and brings the scientists another step closer to their goal of an x-ray laser.

In comparison with the best existing light sources used for research operating in the regime of extremely hard ultraviolet radiation, the new laser has more than a thousand times the peak brightness. Compared to state-of-the-art synchrotron radiation sources, the scientists report that the gain in peak brightness is greater than a million. These results were achieved using a FEL that produced ultraviolet laser light with wavelengths ranging from 80 to 180 nm, with maximum saturation demonstrated at 98 nm. Intensive laser light was produced using a new method in which electrons were brought to high energies in a superconducting accelerator and then sent traversing a 15-m-long, slalomlike course of a special arrangement of magnets (the undulator), resulting in laserlike bundles of radiation. Contact Petra Folkerts at [email protected].

Aperiodically poled lithium niobate yields active tunable frequency converter
Researchers at Universidad Miguel Hernández (Elche, Spain) and the Universidad Autónoma de Madrid (Cantoblanco, Spain) have used aperiodically poled, neodymium-doped lithium niobate to convert the 750- to 850-nm band of a Ti:sapphire laser into tunable continuous-wave laser radiation ranging from 440 to 475 nm and from 485 to 505 nm. The nonlinear crystal in the experimental setup was 4 x 4 mm in cross section and 3 mm long. It had a parabolic chirp in ferroelectric domain sizes ranging from 7 µm in the middle to 3 µm at the ends. The crystal was placed in a quasi-hemispherical laser cavity and pumped by an 809-nm-emitting 2-W diode laser. Once laser oscillation was established at 1084 or 1372 nm, the Ti:sapphire beam was injected into the cavity through the input mirror. The wavelength of the output beam shifted along with the wavelength of the Ti:sapphire input. Sum-frequency mixing with a 1084-nm oscillation yielded the 440- to 475-nm output range, while mixing with a 1372-nm oscillation yielded the 485- to 505-nm range. The system may cover the range from 425 to 610 nm if the Ti:sapphire is allowed to tune between 700 and 1100 nm, though absorption from the ground to excited states can reduce efficiency at some particular wavelengths. Contact Juan Capmany at [email protected].

Annular superconducting tunnel junction detects x-rays
Using an annular niobium (Nb)-based superconducting tunnel junction (STJ), researchers at Yale University (New Haven, CT), Hypres Inc. (Elmsford, NY), and CNR-Instituto di Cibernetica (Naples, Italy) have created a detector of single x-ray photons. In STJ detectors, photons are absorbed and broken down into Cooper pairs, a process that creates excess quasiparticles proportional to the photon energy. A small superconducting energy gap of about 1.5 meV for Nb enables the photon energy to be measured with good intrinsic energy resolution. In the team's novel annular configuration of the STJ, the Josephson critical current is suppressed, trapping fluxons in a ring-shaped junction and thereby avoiding the use of an externally applied magnetic field parallel to the STJ barrier. The detector was cooled through its critical temperature in a magnetic field perpendicular to the plane of the STJ tunnel barrier. The team acquired current pulses from single x-ray photons from a shuttered 55Fe source with emission lines at 5.9 and 6.5 keV. The detector configuration has potential benefits for STJs used in imaging arrays. Contact Luigi Frunzio at [email protected].

Grating is spaced to atomic perfection
Whether used for diffracting electrons or light, gratings containing flaws in their line spacing produce unwanted scatter. A perfect nanoscale grating could not only diffract efficiently, but could also serve as a length scale for photolithographic applications. Researchers at the University of Wisconsin (Madison, WI), the University of Basel (Basel, Switzerland), and the Universität Erlangen-Nürnberg (Erlangen, Germany) have chosen the ultimate in precise units—the atom—to make flawless nanometer-scale gratings.

By cutting silicon at a 9.45° angle relative to the (111) surface, a repeating series of lines arises, where each unit cell contains a triple step (each step an atom high) combined with a single flat area 7 atoms in width. The period of the structure is 5.73 nm and is atomically accurate, meaning that no flaws in spacing exist. Gratings with perfect structure to 10 periods have been created, with longer-range periodicity currently limited by defects of extra rows of atoms. The researchers can passivate the gratings using either methanol or gold with a titanium wetting layer. Contact Franz Himpsel at [email protected].

Photonic-crystal cavity microlasers integrated on silicon wafers
The successful operation of indium phosphide-based two-dimensional photonic-crystal cavity microlasers integrated on a silicon wafer—fabricated by combining hydrophilic wafer bonding and standard nanofabrication procedures—was recently reported by researchers at the Center for Projects in Advanced Microelectronics (Grenoble, France). The researchers demonstrated a laser effect on indium phosphide-based photonic-crystal microcavities on a silicon wafer at room temperature under pulsed optical pumping for various air-filling factors. Compared to suspended membrane cavities, the use of silicon dioxide allowed for better thermal sinking. However, the design and fabrication processes of these structures still must be optimized in order to reduce the laser threshold. Electrical pumping and coupling of the laser beam into a passive optical waveguide are the next steps. The researchers hope that their work will lead to the realization of photonic circuits integrating silicon passive optical components and III-V active devices. Contact Xavier Letartre at

Polishing process makes glass smooth to 0.29 nm
Highly polished optical-glass surfaces are useful for high-finesse Fabry-Perot etalons, low-loss laser mirrors, and other demanding applications. Collaboration between scientists at the National Academy of Sciences of Ukraine (Kiev, Ukraine), L.O.T.-Oriel GmbH & Co. KG (Darmstadt, Germany), and the Central Design Bureau Arsenal (Kiev, Ukraine) has resulted in the fabrication of optical surfaces with a surface roughness of less than 1 nm and a reflected-light scattering factor of less than 0.003%.

The decade-long study began with the testing of spherical laps made of cerium oxide-based Aquapol composites, with four million lenses made. The objective was to eliminate the abrasive microcutting process when machining glass. A melt of the binder components and polishing powder was cast into a mold to create a workpiece surface. Experience resulted in the creation of lower-density, more-elastic polishing composites, which increased contact area between tool and workpiece, increased material removal rate by a factor of 1.5, and decreased the wear rate by a factor of 5. One composite produced surfaces with an average surface roughness of 0.29±;0.09 nm. Contact Valentin Rogov at [email protected].

Optical parametric amplifier yields 10-dB gain over 200 nm
Researchers at Stanford University (Palo Alto, CA), Sumitomo Electric Industries (Yokohama, Japan), and Furukawa Electric Co. (Tokyo, Japan) have obtained more than 10 dB of gain over a 208-nm bandwidth in a fiber optical parametric amplifier (OPA) and observed only minor distortion of the OPA gain spectrum due to the Raman effect. The gain medium in the experimental OPA consisted of 20 m of highly nonlinear fiber preceded by an eight-wavelength, planar-lightwave-circuit, Mach-Zehnder interferometer multiplexer that combined the pump and signal beams. The pump beam was provided by a 1542.4-nm, 13-dBm, distributed-feedback (DFB) laser amplified by cascaded erbium-doped fiber amplifiers and pulse-modulated to about 10 W peak output power. Signals ranging from 1511 to 1593 nm were provided by an external-cavity tunable laser in some experiments. In addition, 1443-, 1466-, 1495- and 1651-nm signals were provided by discrete DFB lasers in other experiments. Upon leaving the gain medium, the amplified signal and the unamplified signal were extracted by cascaded tunable optical filters, then measured with a photodetector and compared on an oscilloscope. The researchers also noted a Raman gain factor on the order of 0.15, indicating a relatively minor Raman effect on the OPA gain spectrum. Contact Min-Chen Ho at [email protected].

Picosecond ultraviolet pulses generated from a modelocked InGaN diode laser
Researchers at the University of California-Santa Barbara (Santa Barbara, CA) have reported successful generation of ultraviolet optical pulses with ultrashort duration from an indium gallium nitride (InGaN) light emitter. By actively modelocking an external-cavity InGaN laser, average output power of 2 mW was achieved at a wavelength of 409 nm with a pulse duration of 30 ps. The cavity of the diode consisted of a diffraction grating with 1200 lines/mm and a semiconductor optical amplifier (SOA). The SOA was created by coating a cleaved facet of a ridge waveguide multiple-quantum-well InGaN diode from Nichia Corp. (Kaminaka, Japan). To achieve active modelocking, the scientists drove the SOA with 20 mW RF power at the cavity round-trip frequency along with 43 mA of direct current using a bias tee. The pulse profile shows a spectral width of 0.023 nm at a center wavelength of 408.5 nm and is temporally asymmetric due to a dynamic detuning effect in active modelocking. Modelocked semiconductor lasers are attractive light sources due to their compact and efficient nature, with potential application in laser marking and lithography. Contact Sang Young Gee at [email protected].

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