Michel Bouriau

Three-dimensional microfabrication by two-photon-initiated polymerization with a low-cost microlaser

Fabrication of submicrometer structures by two-photon-initiated polymerization is performed with an inexpensive and low-power microlaser. This is made possible by the design of photoinitiators with strong two-photon absorption cross sections. We analyze the influence of both material properties and irradiation conditions on the two-photon polymerization rate and show that resins based on our highly sensitive two-photon photoinitiator can be solidified with microlaser excitation, whereas commercial UV photoresins require ultrashort and intense laser pulses.

Optically driven Archimedes micro-screws for micropump application

Archimedes micro-screws have been fabricated by three-dimensional two-photon polymerization using a Nd:YAG Q-switched microchip laser at 532nm. Due to their small sizes they can be easily manipulated, and made to rotate using low power optical tweezers. Rotation rates up to 40 Hz are obtained with a laser power of 200 mW, i.e. 0.2 Hz/mW. A photo-driven micropump action in a microfluidic channel is demonstrated with a non-optimized flow rate of 6 pL/min. The optofluidic properties of such type of Archimedes micro-screws are quantitatively described by the conservation of momentum that occurs when the laser photons are reflected on the helical micro-screw surface.

Optical properties of metallic nanostructures fabricated by two-photon induced photoreduction

We are using the technique of two-photon induced photoprecipitation to fabricate gold and silver nanostructures. Gold and silver nanoparticles are produced in solution as well as in thin films. In both cases an absorption peak associated with the plasmon resonance is clearly observed and is found to vary as particles grow. In addition, we show that this technique also permits the fabrication of 2D and 3D metallic nanostructures with a good quality. The potential for optical applications is discussed and illustrated on some examples. In particular, we observe high efficiency luminescence and strong tunable diffusion.

Optically driven Archimedes micro-screws for micropump applications: multiple blade design

We study the rotation of photo-driven Archimedes screw with multiple blades. The micron-sized Archimedes screws are readily made by the two-photon polymerization technique. Free-floating screws that are trapped by optical tweezers align in the laser irradiation direction, and rotate spontaneously. In this study we demonstrate that the rotation speeds of two-blade-screws is twice the rotation speed of one-blade-screw. However, more complex 3-blade-screws rotate slower than 2-blade-screws due to their limited geometry resolution at this micron scale.

Two-photon induced polymerization of photo-driven microsensors

We report on the fabrication of photo-driven polymer microsensors for viscosimetry, velocimetry and micropump applications. They are readily made with a low-cost polymerization technique based on two-photon absorption. Microsensors are free-floating in the liquid to be characterized. A linearly-polarized optical tweezers is used to trap one sensor at the laser focal point and to generate the optical torque needed for local hydrodynamic measurements. Viscosity and velocity microsensors have slab shapes that align in the polarization direction. The local viscosity is deduced from the maximum rotation frequency generated by the rotating linear polarization, while the fluid velocity is obtained by measuring the maximum angle that equilibrates the optical torque and drag torque. Experimental results are in good agreement with theoretical calculations. The micropump is based on a micron-size Archimedes screw that rotates around its long axis when it is trapped at the focal point. The laser-induced rotation is due to the optical torque that is transferred by the laser scattering on the screw.

Recent advances in two-photon 3D laser lithography with self-Q- switched Nd:YAG microchip lasers

We review our recent results towards the development of a turnkey 3D laser printer, based on self-Q-switched microchip Nd:YAG lasers, with reproducible sub-100nm resolution, and with large-scale (cm) and fast-speed (cm/sec) capability at micron resolution. First of all, we report on line fabrication with 70nm lateral, and 150nm longitudinal resolutions without significant shrinking. This is due to the tight focusing with green visible wavelength, large numerical aperture, and excellent resin properties. Secondly, we report on two-photon sensitive photoacid generators that lead to efficient 3D microfabrication with epoxy SU-8 resin. Thirdly, we demonstrate high-speed microfabrication of large scale, millimeter size, scaffolds and cemtimeter height needle with high repetition rate (130Khz), and high average power (1W) amplified microchip laser. Finally we demonstrate the two-photon induced cross-linking of antibodies to determine the type of red blood cells in microfluidic channels.

Two-photon absorption initiation for polymerization with microlasers at 532 and 1064 nm

We report here the caracterization of efficient photoinitiators for radicalar polymerization by two-photon absorption (TPA). Symmetric molecules bearing tertiary amines as a donor group D and a biphenyl or a fluorene for the transmitting electron group π were proposed for the visible. For IR, the selected phoinitiator presents the general structure D-π-A-π-D, in which A is an acceptor group. The initiation efficiencies of these systems were evaluated by the determination of the threshold intensities for a given exposure duration. Molecules for the visible are more sensitive than those designed for IR. Comparing to the commercial resins for UV photopolymerization generally involved for TPA, these optimized intiators led to a significant increase of the sensitivity during fabrication. Weaker incident intensities and faster scanning speeds could be used. This approach led the fabrication of tridimensional micro-objects with a less onerous nanosecond pulses microlaser.

Nonlinear photochemistry and 3D microfabrication with Q-switched Nd:YAG microchip lasers

We review our recent advances in two-photon induced photochemistry to fabricate three-dimensional micro-objects made in polymers, proteins and noble metals using Q-switched Nd:YAG microchip lasers. We have synthesized a new photoinitiator that is about 4 times more sensitive for two-photon polymerisation with sub-nanosecond pulses at 532 nm. We describe the improvement of our fabrication process and strategies to obtain solid microstructures that correspond to their models. We report on our progress to make silver microstructures by the photoreduction of silver nitrate with microchip lasers at 1064nm.

Laser Beam Trajectory Generation for Micro-Manufacturing With a Two-Photon Polymerization Technique

Micro-manufacturing with a Two-Photon Polymerization (TPP) technique is an emerging manufacturing technique to produce small objects of tens of μm size. Combined with three axes numerically controlled equipment, it becomes possible to produce a wide diversity of product shapes. As a result, controlling this equipment while taking into account the manufacturing constraints raises the problem of trajectory generation. It is the purpose of this paper to show how this trajectory generation process can take advantage of the three numerically controlled axes to produce complex-shaped objects. Here, it is shown how the concept of layered manufacturing commonly used in rapid prototyping can be superseded by a combination of different path planning strategies, much in the same way free-form surfaces or complex shapes can be produced with classical milling machines. Through the proposed process, the boundary decomposition process applied to an object reduces to a set of sub-domains where groups of parallel trajectories are generated. The proposed trajectory generation process takes also into account the manufacturing constraints specific to TPP to produce microstructures of high quality. Examples of products illustrate the proposed approach and demonstrate its capabilities.Copyright