820 nm Colliding-Pulse Modelocked Dye Laser

Abstract

The 620 nm CPM laser has become the most common laser for femtosecond pulse generation, with perhaps as many as several hundred units around the world in operation. The CPM laser, of course, provides direct conversion of CW light to femtosecond modelocked pulses. While it is desirable to extend this technique to other wavelengths, each new wavelength requires a painful and lengthy materials research program, with no guarantee of success. A number of conditions have been investigated [1], but the 620 nm CPM laser is still the most common laser, and one wonders whether the R6G-DODCI pair is the most “magic pair” in existence. We have developed a new CPM laser which operates in single pulse trains of high stability and find performance comparable to 620 nm CPM lasers. A six mirror cavity with gain jet of Rhodamine-800 dye and saturable absorber of HITCI dye is completed with four SF-10 brewster prisms in a standard cavity configuration. Figure 1 shows the relevant spectroscopy. We choose R-800 because it has the longest wavelength emission of the high-quantum efficiency family of rhodamine dyes; this may represent the longest wavelength attainable for CW-pumped CPM dye lasers. We find that direct pumping with an active-stabilized CW krypton laser yields better stability than when pumping with a Ti:Sapphire laser [2], because of the improved mode quality, noise and pointing stability.