Research round-up

16 Feb 2005

A look at some of the innovations in optics unveiled this month.

X-RAY LASER
Researchers in Germany and Austria report a compact X-ray laser that delivers X-ray photons with around ten times the energy produced by previous compact devices. The unit emits highly collimated, spatially coherent X-rays at a wavelength of around 1 nm and with photon energies up to 1.3 kilo-electronvolts. The team's set-up features a multistage titanium:sapphire laser that generates near-infrared pulses of less than 15 femtoseconds. These pulses are then spectrally broadened and compressed by chirped mirrors. The device produces X-rays when the linearly polarized pulses ionize a jet of helium. According to the authors, their compact set-up puts a laboratory source of higher energy X-ray beams within reach. (Nature 433 596)

SPECTROSCOPY
An ancient fresco in Acireale Cathedral, Sicily, is set to benefit from a study performed by Italian scientists. Their work involved the use of Fourier-transform infrared and X-ray diffraction spectroscopy, Raman microspectroscopy, and scanning electron microscopy to reveal the fresco's organic and inorganic origins. X-ray diffraction plays a key role as the analytical technique allows the identification of elements present in both pictorial and plaster layers. By using complementary methods the scientists felt that they could evaluate the fresco's condition in greater detail and so suggest a more accurate restoration strategy. (J. Appl. Phys. 97 044907-1)

LIQUID CRYSTAL LASER
European scientists have demonstrated quasicontinuous tuning of a dye doped cholesteric liquid crystal (CLC) laser. The mirrorless device contains a glass cell in which six dyes are combined to nearly cover the wavelength range from ultraviolet (370 nm) to red (680 nm). Optically pumped, the team tunes its CLC laser by simply moving the cell to the left or right with respect to the excitation source - a pulsed (4 ns, 1 - 10 Hz) 337 nm Nitrogen laser. (Appl. Phys. Lett. 86 051107-1)

PHOTONIC CRYSTALS
Researchers in Canada and the US have come up with a way of fabricating woodpile-type, three-dimensional photonic crystals using phase-mask based lithography. The scientists make their microstructured materials with tetragonal or cubic symmetries by exposing the photoresist to interference patterns generated by two phase masks. By taking advantage of the standard tools of the electronic industry, the authors hope that their work could lead to the mass-production of three-dimensional photonic crystals for applications such as integrated optical circuits. (Appl. Phys. Lett. 86 071117-1)

PICOSECOND LASER
Applications such as external-cavity frequency doubling and telecommunication could all profit from the work of scientists at the Swiss Federal Institute of Technology. The Zurich based team has developed an optically pumped, passively mode-locked, external-cavity semiconductor laser that generates 4.7 ps pulses at 957 nm with a 4 GHz repetition rate and an average power output of 2.1 W. Reseachers use an intracavity etalon to reduce the chirp of the pulses. "For the first time to our knowledge, the performance of a mode-locked picosecond semiconductor laser has reached the level of passively mode-locked solid-state lasers optimized for high power in the multigigahertz regime," say the authors. "Given the rapid progress in high-power VECSELs, we expect that they could soon outperform all other mode-locked lasers in the multiwatt multigigahertz domain." (Optics Letters 30 272)