Laser Raman scattering cools GaN

Dec. 4, 2012
While laser-based optical refrigeration methods are typically based on anti-Stokes fluorescence, researchers at Lehigh University and Johns Hopkins University may soon succeed in cooling gallium nitride (GaN)—which has one of the highest longitudinal optical (LO) phonon energies of any semiconductor material at 91.8 meV—using anti-Stokes Raman scattering.

While laser-based optical refrigeration methods are typically based on anti-Stokes fluorescence, researchers at Lehigh University (Bethlehem, PA) and Johns Hopkins University (Baltimore, MD) may soon succeed in cooling gallium nitride (GaN)—which has one of the highest longitudinal optical (LO) phonon energies of any semiconductor material at 91.8 meV—using anti-Stokes Raman scattering.

A frequency-doubled Ti:sapphire laser (tunable from 370–389 nm) illuminates an undoped, 1-µm-thick GaN film. Anti-Stokes and Stokes signals are collected by a spectrometer and detected by a photomultiplier tube. The laser radiation is then optimized to have an LO phonon energy lower than that of the bandgap of GaN, maximizing the anti-Stokes Raman intensity while eliminating the emission of hot LO phonons through photogenerated carriers that could cause GaN heating. It turns out that the spectral dependence of Stokes and anti-Stokes Raman signals is quite different. As pump wavelength is varied, laser cooling occurs if the anti-Stokes Raman intensity is enhanced by a factor of 2.0, making it equal to the Stokes signal and reaching the threshold for GaN cooling. To meet this Stokes/anti-Stokes signal equality requirement, the researchers plan to use an optical resonator only resonating at the wavelength of the anti-Stokes signal to enhance the signal by a factor of 2.0. Contact Yujie Ding at[email protected].

Sponsored Recommendations

Request a free Micro 3D Printed sample part

April 11, 2024
The best way to understand the part quality we can achieve is by seeing it first-hand. Request a free 3D printed high-precision sample part.

How to Tune Servo Systems: The Basics

April 10, 2024
Learn how to tune a servo system using frequency-based tools to meet system specifications by watching our webinar!

Motion Scan and Data Collection Methods for Electro-Optic System Testing

April 10, 2024
Learn how different scanning patterns and approaches can be used in measuring an electro-optic sensor performance, by reading our whitepaper here!

How Precision Motion Systems are Shaping the Future of Semiconductor Manufacturing

March 28, 2024
This article highlights the pivotal role precision motion systems play in supporting the latest semiconductor manufacturing trends.

Voice your opinion!

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