Frequency-doubled degenerate laser is speckle-free green light source

Nov. 4, 2016
Laser-based projection displays from cinema-sized sources to picoprojectors combine the light from red, green, and blue lasers to achieve full-color projection.

Laser-based projection displays from cinema-sized sources to picoprojectors combine the light from red, green, and blue lasers to achieve full-color projection. Speckle, a characteristic of narrowband lasers, degrades the viewing experience—because many laser-projection illuminators rely on wider-bandwidth blue and red laser diodes and a narrower-bandwidth green laser (for example, a frequency-doubled YAG laser), it is green that has traditionally been most difficult to despeckle. Now, a group from Yale University (New Haven, CT) and TRUMPF (Farmington, CT) has developed an intracavity frequency-doubled degenerate laser that has low spatial coherence (on the order of 3300 transverse modes) and thus low speckle. The researchers say the laser will be useful both for biomedical imaging (for example, fluorescence excitation for microscopy) and full-color projection displays.

The laser is so-called "degenerate" because its cavity is carefully designed so that there are many mutually incoherent modes for which lasing is equally likely. It consists of a frequency-doubled diode-pumped neodymium (Nd)-vanadate (YVO4) disk in contact with a heat sink, and intracavity frequency-doubled using a potassium titanyl phosphate (KTP) crystal with a large angular bandwidth for type II phase matching. Using fluorescence imaging through a microscope as a check, the researchers compared the new green light source to a conventional frequency-doubled diode-pumped solid-state (DPSS) laser—while the conventional source produced fringes and rings in the image, the low-coherence source produced an artifact-free image. Reference: S. F. Liew et al., arXiv:1609.05534v1 (Sept. 18, 2016).

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.

Sponsored Recommendations

Advancing Neuroscience Using High-Precision 3D Printing

March 7, 2025
Learn how Cold Spring Harbor Laboratory Used High-Precision 3D Printing to Advance Neuroscience Research using 3D Printed Optical Drives.

From Prototyping to Production: How High-Precision 3D Printing is Reinventing Electronics Manufacturing

March 7, 2025
Learn how micro 3D printing is enabling miniaturization. As products get smaller the challenge to manufacture small parts increases.

Sputtered Thin-film Coatings

Feb. 27, 2025
Optical thin-film coatings can be deposited by a variety of methods. Learn about 2 traditional methods and a deposition process called sputtering.

What are Notch Filters?

Feb. 27, 2025
Notch filters are ideal for applications that require nearly complete rejection of a laser line while passing as much non-laser light as possible.

Voice your opinion!

To join the conversation, and become an exclusive member of Laser Focus World, create an account today!