Optical waveguide fabrication and integration with a micro-mirror inside photosensitive glass by femtosecond laser direct writing

Photosensitive glass is a potentially important material for micro-fluidic devices that can be integrated with micro-optical components for biochemical analysis. Here, we demonstrate the fabrication of optical waveguides inside glass by femtosecond laser direct writing. The influence of the laser parameters on the waveguide properties is investigated, and it is revealed that the waveguide mode can be well controlled. The single mode is achieved at a low writing energy, while the multimode is achieved with increasing energy. In spite of a longitudinally elongated elliptical shape of the cross-sectional profile, the far-field pattern of the single-mode waveguide shows an almost symmetric profile. The measured propagation loss and the coupling loss are evaluated to be ∼0.6 dB/cm and ∼1.6 dB at a wavelength of 632.8 nm, respectively, under the conditions of 1.0–2.0 μJ pulse energy and 200–500 μm/s scan speed. The increased optical loss is associated with a higher waveguide mode at higher writing energy. Furthermore, the integration of waveguides and a micromirror made of a hollow microplate inside the glass is demonstrated to bend the laser beam at an angle of 90° in a small chip. The bending loss is estimated to be smaller than 0.3 dB. PACS 42.62.-b; 42.82.Cr; 82.50.Pt; 42.79.Gn; 42.81.Qb     

Electronic effect on the regioselectivity in the ring opening of para-substituted phenyloxiranes by acetylides

The electronic effect on the regioselectivity in the alkynylation of phenyloxiranes was investigated using three kinds of metal acetylides. BF₃ mediated lithium acetylide provided either the α- or β-alkynylated products by controlling the effect of the para-substituents of the phenyloxiranes. LiClO₄ mediated lithium acetylide and titanium acetylide, on the other hand, afforded predominantly the β- and α-products, respectively.     

Facile peptide thioester synthesis via solution-phase tosylamide preparation

Preparation of peptide thioester is essential for native chemical ligation and block condensation. Our novel methodology involves conversion of the carboxylic acid of a peptide into a thioester using p-toluenesulfonyl isocyanate, followed by alkylation, then thiol substitution. Our methodology can also be used for the preparation of glycopeptide thioesters. Furthermore, it is possible to carry out the reaction as a sequential peptide chemical ligation.     

Temperature effect on solubilization of n-alkylbenzenes into sodium cholate micelles

The solubilization of n-alkylbenzenes (benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, n-hexylbenzene) into an aqueous micellar solution of sodium cholate was carried out. Solubilizate concentrations at equilibrium were determined spectrophotometrically at 293.2, 298.2, 303.2, 308.2, and 313.2 K. The first stepwise association constants (K(1)) between solubilizate monomers and vacant micelles were evaluated from the equilibrium concentrations and found to increase with increasing hydrophobicity of the solubilizate molecules. From the Gibbs energy change for solubilization at different micelle aggregation numbers and from the molecular structure of the solubilizates, the function of sodium cholate micelles as solubilizer was discussed. Enthalpy and entropy changes of solubilization were calculated from the temperature dependence of the K(1) values, and the solubilization was found to be enthalpy-driven for the solubilizates with shorter alkyl chains. The results obtained were also compared with those for conventional aliphatic micelles.     

A microfluidic chip integrated with a microoptical lens fabricated by femtosecond laser micromachining

We report on the integration of microlens and microfluidic channels in fused silica glass chip using femtosecond laser micromachining. The main process includes three procedures: (1) femtosecond laser scanning for forming a hemispherical surface and a Y-shaped channel in the fused silica glass; (2) chemical etching of the sample for removal of the modified areas; and (3) oxyhydrogen (OH) flame polish for smoothening the surface of the microlens. In addition, we demonstrate that the fabricated microlens exhibits good imaging performance with a 5× magnification, showing great potential in future lab-on-a-chip applications.     

Fabrication of microfluidic optical waveguides on glass chips with femtosecond laser pulses

We describe the fabrication of microfluidic channel structures on the surface of a borosilicate glass slide by femtosecond laser direct writing for optical waveguide application. Liquid with a variable refractive index is fed into the microchannel, serving as the core of the waveguide. We demonstrate that either a multimode or a single-mode waveguide can be achieved by controlling the refractive index of the liquid.     

Fabrication of microchip based on UV transparent polymer for DNA electrophoresis by F2 laser ablation

A microchip for DNA electrophoresis made of a new UV transparent polymer material (CYTOP) whose absorption edge is much shorter than 190 nm has been fabricated by F₂ laser ablation. F₂ laser ablation achieves high-quality microfabrication of CYTOP surface with little deterioration of the optical property and little debris deposition at etched area. The microchip in which the microchannel connected with two reservoirs was embedded was successfully fabricated by bonding the ablated sample to the virgin CYTOP sheet. The fabricated microchip was applied for DNA analysis by electrophoresis and succeeded in separating different base-pares (bp) of DNA from 50 to 766 bp with resolution of 100 bp. PACS 42.70.Jk; 52.38.Mf; 82.45.-h     

Direct photoetching of single crystal SiC by VUV-266 nm multiwavelength laser ablation

2 O₂:H₂O and HF:H₂O. The analysis of the etched samples by scanning electron microscopy (SEM) and scanning probe microscopy (SPM) indicates that an array of square holes having well-defined patterned structures and clean substrate surfaces were obtained. The X-ray photoelectron spectroscopy (XPS) analysis indicates that the SiC samples etched by VUV-266 nm multiwavelength laser have a similar stoichiometry after chemical post-treatment as the virgin SiC. The mechanism of high-quality ablation using VUV-266 nm multiwavelength laser is discussed in comparison with ablation using 266 nm single wavelength. The chemical post-treatment contributes to removing the residues from the laser photolysis of SiC. Received: 26 August 1996/Accepted: 17 October 1996