On-chip microfabricated capillaries for hyper Rayleigh scattering of nonlinear optical organic molecules

Deep wet etching of fused silica glass for hollow capillary optical leaky waveguides in microfluidic devices

“…Since the fluid typically has a refractive index below that of the device material fused silica (fluid: n fluid = 1.33-1.45 dependent on wavelength, n fused silica = 1.45 at 840 nm), the resulting waveguide is called an optical leaky waveguide [9]. We have measured the waveguide attenuation to be 0.15 dB mm −1 and the end-fire coupling loss to be 1.2 dB (waveguide diameter of about 64 µm, wavelength 840 nm, dioxane filling) [6]. This confirms good optical waveguiding which results in an interaction zone with high light intensities inside the capillary.…”

“…(2) large optical transmission range (180-2500 nm) and low optical absorption; (3) high electrical insulation (specific electrical resistivity of 10 20 m at 20 • C); and (4) low, defined interaction with all common solvents. These properties make fused silica very useful for many applications, for example, for capillary electrophoresis [4,5] and hyper Rayleigh scattering [6,7].…”

“…We have earlier demonstrated that a high efficiency of interaction between a fluid, i.e. mostly a diluted substance, and a light source is achieved by waveguiding in a capillary [6,7,9]. The capillary is simultaneously used as fluid carrying medium and optical leaky waveguide.…”

Ultradeep fused silica glass etching with an HF-resistant photosensitive resist for optical imaging applications

“…To avoid the use of specialized equipment, there has recently been an effort to adapt wafer-scale processing methods to glass, namely, reactive ion etching and lithographically-defined 'wet' etching. These methods have enabled the realization of a variety of devices including free-standing air cavities [2], micropumps [8], capillary electrophoresis microchambers [1,9], high Q-factor resonators [10], microfluidic channels [11,12], waveguides [13], bioanalytical devices [14] and single cell trapping wells [3], planar patch-clamp electrodes [15], and optical sensing platforms [1,3].…”

“…As a result, relatively high biases are required when etching glass which compromises the masking material choice, smoothness of the etched surface, and attainable etch depth [17][18][19][20] [21,23], fused silica still has the advantage of chemical purity which makes it compatible with CMOS processing techniques [3] and eliminates substrate autofluorescence [24]. Previous masking film materials for fused silica have included chromium (Cr) [25], photoresists [13], polysilicon (polySi), amorphous silicon, aluminum, silicon nitride, and chromium/gold (Cr/Au) [3]. For example, fused silica was wet etched 60 m deep with a Cr/Au mask in 49% HF for 1 hour [ μ 3] and 104 m deep with a μ stress-reduced Cr mask in a heated buffered ammonium fluoride solution for 7 hours [25].…”