Tag: coherent beam combination

50W CW visible laser source at 589nm obtained via frequency doubling of three coherently combined narrow-band Raman fibre amplifiers

Luke R. Taylor, Yan Feng, and Domenico Bonaccini Calia

Optics Express, Vol. 18, Issue 8, pp. 8540-8555 (2010) doi:10.1364/OE.18.008540

Abstract: We demonstrate the cascaded coherent collinear combination of a seed-split triplet of 1178nm high-power narrow-band (sub-1.5MHz) SBS-suppressed CW Raman fibre amplifiers via nested free-space constructive quasi-Mach-Zehnder interferometry, after analysing the combination of the first two amplifiers in detail. Near-unity combination and cascaded-combination efficiencies are obtained at all power levels up to a maximum P1178 > 60W. Frequency doubling of this cascaded-combined output in an external resonant cavity yields P589 > 50W with peak conversion efficiency η589 ~85%. We observe no significant differences between the SHG of a single, combined pair or triplet of amplifiers. Although the system represents a successful power scalability demonstrator for fibre-based Na-D2a-tuned mesospheric laser-guide-star systems, we emphasise its inherent wavelength versatility and consider its spectroscopic and near-diffraction-limited qualities equally well suited to other applications.

This work was to demonstrate the scalability of the Raman fiber amplifier approach. As one can imagine, we had worked hard to break the published record power of 50 W by the Starfire people. 🙂

A new publication is out: Yan Feng, Luke R. Taylor, and Domenico Bonaccini Calia, “25 W Raman-fiber-amplifier-based 589 nm laser for laser guide star,” Opt. Express 17, 19021-19026 (2009)

We report on a 25 W continuous wave narrow linewidth (< 2.3 MHz) 589 nm laser by efficient (> 95%) coherent beam combination of two narrow linewidth (< 1.5 MHz) Raman fiber amplifiers with a Mach-Zehnder interferometer scheme and frequency doubling in an external resonant cavity with an efficiency of 86%. The results demonstrate the narrow linewidth Raman fiber amplifier technology as a promising solution for developing laser for sodium laser guide star adaptive optics.

Basically it is a journal paper on the results I reported at CLEO Europe 2009 in Munich. It took almost three months to go through the review process, on an Express journal which supposes to extremely fast. The process is slow probably because the associated editor is busy. What is really odd is that the comments from one of the reviewers are apparently referring to another paper.

The process is so slow that the results are not up to date anymore. In these months, we have scaled the power from a single amplifier by a factor of two. Now we are able to obtain more than 25 W <2.3 MHz linewidth 589 nm laser with frequency doubling of a single narrow linewidth Raman fiber amplifier, which is the topic of our forth-coming Frontiers in Optics postdeadline paper: Yan Feng, Luke Taylor, Domenico Bonaccini Calia, Ronald Holzlöhner, and Wolfgang Hackenberg, 39 W narrow linewidth Raman fiber amplifier with frequency doubling to 26.5 W at 589 nm, PDPA4, Oct. 14, 2009，San Jose, California, USA. We have actually obtained 28 W right now. My colleague Ronald Holzlöhner will attend the conference and give the presentation.