Low noise Raman lasers for yellow-orange spectrum coverage

Abstract

Diode lasers have been demonstrated to operate over a great part of the visible spectrum: InGaN diodes cover the violet-blue- green part ( 635 nm). Some fluorophorus in biotechnology applications are excited by intermediate wavelengths, from 540 to 630 nm. Optically pumped InGaAs lasers were demonstrated from 460 nm up to 580 nm. Standard frequency doubled diode pumped solid state (DPSS) lasers lack of suitable transition to cover the 565-650nm region. It is possible to modify the semiconductor composition to extend the frequency range or to frequency mix DPSS laser wavelengths, but it comes either with a significant R&D effort or with a complexity in the design. Raman scattering can red-shift the strong transitions of Nd or Yb lasers so that many wavelengths lying in the 1080-1300 nm range can be achieved. Recently several CW diode pumped Raman lasers were demonstrated, some of them including intra-cavity frequency doubling or mixing. The problems with these Raman lasers are the high pump threshold and the high noise. Based on monolithic cavities, we have built several visible Raman lasers with a reduced loss presenting a low pump threshold (<1W) and a high slope efficiency. Output powers in excess of 100 mW were achieved at 588 nm with a 2.5W 808 nm pump. Laser emissions from 556 nm up to more than 610 nm were demonstrated. Noise of these lasers was analyzed and means to reach low noise operation will be discussed at the conference.