Femtosecond lasers have unique characteristics of ultrashort pulse width and extremely high peak intensity; however, one of the most important features of femtosecond laser processing is that strong absorption can be induced only at the focus position inside transparent materials due to nonlinear multiphoton absorption. This exclusive feature makes it possible to directly fabricate three-dimensional (3D) microfluidic devices in glass microchips by two methods: 3D internal modification using direct femtosecond laser writing followed by chemical wet etching (femtosecond laser-assisted etching, FLAE) and direct ablation of glass in water (water-assisted femtosecond laser drilling, WAFLD). Direct femtosecond laser writing also enables the integration of micromechanical, microelectronic, and microoptical components into the 3D microfluidic devices without stacking or bonding substrates. This paper gives a comprehensive review on the state-of-the-art femtosecond laser 3D micromachining for the fabrication of microfluidic, optofluidic, and electrofluidic devices. A new strategy (hybrid femtosecond laser processing) is also presented, in which FLAE is combined with femtosecond laser two-photon polymerization to realize a new type of biochip termed the ship-in-a-bottle biochip.

True three-dimensionally (3D) integrated biochips are crucial for realizing high performance biochemical analysis and cell engineering, which remain ultimate challenges. In this paper, a new method termed hybrid femtosecond laser microfabrication which consists of successive subtractive (femtosecond laser-assisted wet etching of glass) and additive (two-photon polymerization of polymer) 3D microprocessing was proposed for realizing 3D "ship-in-a-bottle" microchip. Such novel microchips were fabricated by integrating various 3D polymer micro/nanostructures into flexible 3D glass microfluidic channels. The high quality of microchips was ensured by quantitatively investigating the experimental processes containing "line-to-line" scanning mode, improved annealing temperature (645°C), increased prebaking time (18 h for 1mm-length channel), optimal laser power (1.9 times larger than that on the surface) and longer developing time (6 times larger). The ship-in-a-bottle biochips show high capabilities to provide simultaneous filtering and mixing with 87% efficiency in a shorter distance and on-chip synthesis of ZnO microflower particles.

In this paper, we develop a technique for realizing multi-centimeter-long lithium niobate on insulator (LNOI) waveguides with a propagation loss as low as 0.027 dB/cm. Our technique relies on patterning a chromium thin film coated on the top surface of LNOI into a hard mask with a femtosecond laser followed by chemo-mechanical polishing for structuring the LNOI into the waveguides. The surface roughness on the waveguides was determined with an atomic force microscope to be 0.452 nm. The approach is compatible with other surface patterning technologies, such as optical and electron beam lithographies or laser direct writing, enabling high-throughput manufacturing of large-scale LNOI-based photonic integrated circuits.

The high-precision integration of three-dimensional (3D) microoptical components into microfluidics in a customizable manner is crucial for optical sensing, fluorescence analysis, and cell detection in optofluidic applications; however, it remains challenging for current microfabrication technologies. This paper reports the in-channel integration of flexible two-dimensional (2D) and 3D polymer microoptical devices into glass microfluidics by developing a novel technique: flat scaffold-supported hybrid femtosecond laser microfabrication (FSS-HFLM). The scaffold with an optimal thickness of 1-5 mm is fabricated on the lower internal surface of a microfluidic channel to improve the integration of high-precision microoptical devices on the scaffold by eliminating any undulated internal channel surface caused by wet etching. As a proof of demonstration, two types of typical microoptical devices, namely, 2D Fresnel zone plates (FZPs) and 3D refractive microlens arrays (MLAs), are integrated. These devices exhibit multicolor focal spots, elongated (.three times) focal length and imaging of the characters 'RIKEN' in a liquid channel. The resulting optofluidic chips are further used for coupling-free white-light cell counting with a success rate as high as 93%. An optofluidic system with two MLAs and a W-filter is also designed and fabricated for more advanced cell filtering/counting applications.

We describe the fabrication of a Mach-Zehnder optical modulator in LiNbO 3 by femtosecond laser micromachining, which is composed of optical waveguides inscripted by a femtosecond laser and embedded microelectrodes subsequently fabricated using femtosecond laser ablation and selective electroless plating. A half-wave voltage close to 19 V is achieved at a wavelength of 632.8 nm with an interaction length of 2.6 mm. This simple and cost-effective technique opens up new opportunities for fabricating integrated electro-optic devices. © 2008 Optical Society of America OCIS codes: 130.0250, 140.3390, 230.2090 Lithium niobate ͑LiNbO 3 ͒ is one of the most widely used nonlinear optic materials in integrated optics owing to its excellent nonlinear optical and electrooptic (EO) properties. Integrated EO devices based on waveguiding structures such as optical switches [1] and modulators [2,3] have gained significant attention. Conventionally, the waveguide fabrication is based on titanium diffusion or proton exchange, which permits fabrication of channel waveguides only close to the surface [4]. Recently, it has been demonstrated that buried optical waveguides in LiNbO 3 can be fabricated by femtosecond laser inscription [5], which opens the possibility to write 3D optical circuits in the crystal. Various fabrication parameters have been optimized by several groups [6][7][8], such as wavelength, repetition rate, polarization, pulse width, pulse energy, focusing geometry, and scanning speed. To realize integrated EO devices, it is further crucial to design and fabricate microelectrodes, which are usually obtained by use of lithographic methods. However, owing to the inherently planar nature of the lithographic process, this technique is limited in its capability to produce 3D structures. Furthermore, because the optical waveguides fabricated by femtosecond laser inscription usually are deeply buried in the crystal, the conventional surface electrodes give rise to weak EO interaction. As a simple and costeffective technique, laser-induced selective electroless deposition has been widely investigated, because it does not require fabrication steps involved in the traditional lithographic technique, such as deposition of thin layers of metals, pattern etching, and so on [9,10]. Recently, we developed a technique for selective metallization in LiNbO 3 using femtosecond-laser ablation and femtosecond-laser-assisted selective electroless plating, which allows for fabricating microelectrodes deeply embedded in LiNbO 3 [11]. In this Letter, we report the integration of embedded microelectrodes and optical waveguides in LiNbO 3 using a femtosecond laser. Based on this technique, a Mach-Zehnder interferometer (MZI) EO modulator in an x-cut LiNbO 3 crystal is demonstrated.For the fabrication of waveguides and electrodes, a Ti:sapphire laser system (Legend USP, Coherent Inc.) with an operation wavelength of 800 nm, a pulse width of ϳ40 fs, and a repetition rate of 1 KHz was used. Commercially available MgO-doped x-cut LiNbO 3 crystals...

Surface-enhanced fluorescence from porous, metallic sculptured thin films ͑STFs͒ was demonstrated for sensing of bacteria in water. Enhancement factors larger than 15 were observed using STFs made of silver, aluminum, gold, and copper with respect to their dense film counterparts. The STFs used are assemblies of tilted, shaped, parallel nanowires prepared with several variants of the oblique-angle-deposition technique. Comparison between the different films indicates that the enhancement factor is higher when the tilt is either small ͑Ͻ30 deg͒ or large ͑Ͼ80 deg͒; thus, the enhancement is higher when only a single resonance in the nanowires is excited.

Size-controllable monodisperse PbSe and PbSe/PbS nanocrystals (NCs) have been successfully synthesized with a solvothermal method. Octadecylamine (ODA) molecules were found effective in organizing the nanocrystals to form an ordered monolayer. It is expected that these narrow-band-gap semiconductor NCs with tunable size would have potential applications in near- and mid-IR telecommunication laser sources, electroluminescence, and solar cell materials.

Optimal design and fabrication of novel devices for high-performance optofluidic applications is a key issue for the development of advanced lab-on-a-chip systems.