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19 May 2005
A look at some of the innovations in optics unveiled this month.
OLEDs
A joint effort between Philips and Novaled claims to have produced a high-brightness white OLED with record efficiency. The device has a power efficiency of 25 lm/W and a brightness of 1000 cd/m2. The record was achieved by combining Philips' material and optical out-coupling know-how with Novaled's doping technology. "Our proprietary doping technology is the key to increasing the efficiency through lower voltages," said Novaled's CEO Gildas Sorin.
LITHOGRAPHY
Scientists in the US have developed a microlens array with integrated pores that can be used as a multipattern photomask. Typically, photolithography requires different photomasks to produce features of different sizes. However, the team from Pennsylvania University, MIT and Bell Laboratories uses its single mask design to make various structures by simply adjusting the illumination dose and distance between the lens array and photoresist. "This lithographic method may represent an attractive approach for fast and mass production of submicron periodic structures at low-cost," say the researchers in their paper. (Appl. Phys. Lett. 86 201121)
SENSORS
The measurement of marine phytoplankton, an indicator of climate regulation and carbon cycling, could become much easier thanks to the work of researchers at Hong Kong Baptist University, China. Scientists have devised a flow cytometer that can operate underwater for days and features laser Doppler equipment for defining the measurement volume and determining particle speed. According the team, its optical set-up helps eliminate sample preparation and is a major improvement over existing techniques. (OPTICS LETTERS 30 1087)
LASERS
Researchers in the UK have managed to efficiently generate femtosecond pulses at 524 nm using a periodically poled LiTaO3 crystal to single-pass frequency double the output of a diode-pumped, passively mode-locked Yb3+:KY(WO4)2 laser. "An average output power of up to 120 mW was generated with an internal conversion efficiency of 40%," said the team from St. Andrews University and The University of Southampton. The set-up gives green pulses as short as 225 fs at a pulse repetition of 86 MHz and could benefit applications such as time-resolved spectroscopy and the study of biological and medical samples. (OPTICS LETTERS 30 1144)
SPECTROSCOPY
A US team has developed a ball lens coupled fiber-optic probe that collects nearly four times as much fluorescence signal from the top layer of a two layered test sample compared with a straight-fiber configuration. Coupled to depth-resolved spectroscopy apparatus, the probe could help spot cancer in organs such as the uterine cervix and esophagus. The University of Texas design features a central single collection fiber and two off-axis illumination fibers powered by a xenon light source. (OPTICS LETTERS 30 1159)
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