Microfabricated Dye Lasers

Anders Kristensen, Morten Gersborg-Hansen, Mads Brøkner Christiansen, Søren Balslev, Mikkel Schøler, Daniel Nilsson

Light sources that can be integrated onto lab-on-a-chip micro-systems are of high interest for on-chip spectral analysis of chemical samples [1]. For these applications dye lasers are of particular interest due to the possibility of tuning the wavelength in the visible range. Such applications have stimulated an increasing effort in realizing chip based dye lasers by glass or polymer microfabrication [2-10].

We present a technology for miniaturized, polymer based lasers, suitable for integration with planar waveguides and microfluidic networks. The lasers rely on the commercial laser dye Rhodamine 6G as active medium, and the laser resonator is defined in a thin film of polymer on a low refractive index substrate. Two types of devices are demonstrated: microfluidic- and solid polymer dye lasers. In the microfluidic dye lasers [2-8], the laser dye is dissolved in a suitable solvent and flushed though a microfluidic channel, which has the laser resonator embedded. For solid state dye lasers [9-10], the laser dye is dissolved in the polymer forming the laser resonator. The miniaturized dye lasers are optically pumped by a frequency doubled, pulsed Nd:YAG laser (at 532 nm), and emit at wavelengths between 560 nm and 590 nm. The lasers emit in the plane of the chip, and the emitted light is coupled into planar polymer waveguides on the chip. The feasibility of three types of polymers is demonstrated: SU-8, PMMA and a cyclo-olefin co-polymer (COC) - Topas. SU-8 is a negative tone photoresist, allowing patterning with conventional UV- [9,10] or e-beam lithography [11]. PMMA and Topas are thermoplasts, which are patterned by nanoimprint lithography (NIL)[13,14]. The lasing wavelength of the microfluidic dye lasers can be coarse tuned over 30 nm by varying the concentration of laser dye, and fine tuned by varying the refractive index of the solvent. This is utilized to realize a tunable laser, by on-chip mixing of dye, and two solvents of different index of refraction [8]. The lasers were also integrated with waveguides and microfluidic networks [15].

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[10] S. Balslev, A. Mironov, D. Nilsson, and A. Kristensen, Opt. Express, (2006) accepted for publication
[11] S. Balslev, T. Rasmussen, P.Shi, and A. Kristensen , J. Micromech.Microeng 15 (2005) 2456-2460.
[12] M. Gersborg-Hansen and A. Kristensen, Appl. Phys. Lett., in press (2006)
[13] D. Nilsson, T. Nielsen, and A. Kristensen, Rev. Sci. Instr. 75 (2004) 4481-4486.
[14] D. Nilsson, S. Balslev , and A. Kristensen, J. Micromech. Microeng. 15 (2005) 296-300.
[15] S. Balslev, A. M. Jorgensen, B. Bilenberg, K. B. Mogensen, D. Snakenborg, O. Geschke, J. P. Kutter, and A. Kristensen, Lab. Chip. 6 (2006) 213-217.

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