Towards new type of optofluidic dye lasers fabricated by femtosecond laser (Conference Presentation)

Abstract

Microfluidic lasers are very attractive sources for integrated lab-on-chip systems, medicine, spectroscopy, and many more. Although there have been already variety of impressive results on microfluidic dye lasers, the complexity of fabrication of such systems is still not fully tackled. We propose a new concept for microfluidic channel fabrication that allows to fabricate any shape of micro-channel with a single bulk material and laser processing. We use a femtosecond laser machining for locally modifying the material, followed by wet chemical etching with a bath of 2.5 % HF solution. The final step is the closure of the channel that is done with laser reflow by scanning a CO2 laser over the elongated channel in which the dye is passing through. As a result, we can fabricate channels with various diameters and cross-section shapes ranging from ~10 µm to hundreds of microns and this, over any arbitrary length. Based on this, we setup a dye laser experimental setup. We use Rhodamine 6G as a dye with dimethyl sulfoxide (DMSO) as solvent, with 0.15 g/l of concentration. Since DMSO has slightly higher refractive index than fused silica (1.478 at 570 nm), the microfluidic channel will be able to guide light. For forming a cavity we use gold coated fused silica pieces with cylindrical shape. For pumping, a commercially available special green laser (Necsel) at 532 nm is used, with a maximum power of 2.5 W. With a help of a collimating aspherical and focusing cylindrical lenses we match the pump beam size to the micro-channel size at the focus. Here, we report the working principle of this optofluidic laser, its preliminary performances as well as the various fabrication steps and in particular, the laser-based closing mechanism for the fluidic cavity. We will also introduce a laser cavity in which the dye is constantly refreshed.