Although diode-pumped solid-state (DPSS) lasers are commonly used in biomedical imaging systems, they do have some drawbacks, including a large footprint and high power consumption. In an effort to tackle these problems, Opnext Inc. says that it has developed a high-power violet-laser diode that overcomes the size and power constraints associated with standard DPSS technologies. Among other applications, this diode is suitable for illuminating tissue samples in medical diagnostic applications.

The HL40023MG diode is manufactured using a gallium nitride-material structure that's sometimes known as a three-five band-gap semiconductor, remarks Bob Murphy, director of business development, North American sales, at Opnext. Relying on materials sciences and semiconductor fabrication techniques, the company has created a high-power violet-laser diode that operates at the 404-nm wavelength.

Traditionally, illumination at the 404-nm and other wavelengths has been achieved using diode-pumped solid-state laser assemblies, Murphy explains. However, such diodes can be difficult to manufacture and are larger than semiconductor-based technologies. The advantage of a semiconductor laser is its size, weight, direct modulation, and power consumption, according to Murphy. Thus, the diode features a 5.6-mm package size, has an operating current of 390 mA, and provides 400 mW of optical output power.

"If you compare a DPSS laser at any particular output power, it is fundamentally different from our technology," Murphy comments. For example, a DPSS laser uses an 808-nm pump laser to achieve a wavelength comparable to that of Opnext's 404-nm violet-laser diode. In addition, filters and assembly techniques are required to achieve 404 nm, which demands larger materials inventories. "In other words, the DPSS assembly process makes it a little more difficult to achieve what the HL40023MG does as a semiconductor laser," Murphy says.

Another advantage of a semiconductor laser is its efficiency. A diode's efficiency, according to Murphy, is a more important criterion of its functionality than how much power it consumes or outputs. "Because a diode-pumped solid-state laser squanders much of its power, it typically exhibits very low efficiency. Some DPSS lasers offer 5% efficiency, while others offer 7%," he says. In contrast, a semiconductor solution at an equal output power exhibits anywhere from 20 to 30% power efficiency.

Opnext's violet-laser diode can be employed in three primary medical imaging technologies: confocal laser microscopy, flow cytometry, and particle detection. These techniques are often used in diagnostic applications in which tissue samples are stained with a dye or reagent and then illuminated. "When the material being analyzed fluoresces, you can then differentiate what it is you're looking at down to the molecular level," Murphy adds. "That's one example of how the HL40023MG can be used to perform medical diagnostics."

Opnext Inc.
Fremont, CA
www.opnext.com