Raman Excited Spin Coherences for Turbulence Imaging
Abstract
The objective of this project was to explore the feasibility of using Raman excited spin coherence for turbulence imaging. We experimentally demonstrated that it is possible to use degenerate four-wave mixing (DFWM) in Na vapor to correct intracavity high-speed turbulence aberrations. The use of sodium vapor as a phase conjugate mirror (PCM) provides gains greater than unity and an ideal response time of about 16 nsec, even with cw laser pump beams. We demonstrated a cw degenerate phase conjugate resonator (PCR) using Na vapor with a very low lasing threshold of 4.5 W/cm2 of pump intensity. This low power threshold is produced by DFWM based on coherent population trapping (CPT) in Na vapor when operating close to the Dl transition. The intracavity turbulence was created by a He jet from a nozzle that was driven at the nozzle's resonance of 18 kHz. In the intracavity turbulence correction experiment, a typical intensity for the forward and reverse DFWM pump beams is 10W/ cm2. This experiment provided a low-threshold PCR involving a double-A CPT interaction that produced a correction factor of 9.6 for the temporal aberrations caused by an 18 kHz intracavity turbulence with a flow rate of 250 m/s.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1999
- Accession Number
- ADA408358
Entities
People
- Selim Shahriar
- Shaoul Ezekiel
Organizations
- Massachusetts Institute of Technology