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This paper reports using femtosecond laser marker to fabricate the three-dimensional interior microstructures in one closed flow channel of plastic substrate. Strip-like slots in the dimensions of 800 μm×400 μm×65 μm were ablated with pulse Ti:sapphire laser at 800 nm (pulse duration of ∼120 fs with 1 kHz repetition rate) on acrylic slide. After ablation, defocused beams were used to finish the surface of microstructures. Having finally polished with sonication, the laser fabricated structures are highly precise with the arithmetic roughness of 1.5 and 4.5 nm. Fabricating such highly precise microstructures cannot be accomplished with nanosecond laser marking or other mechanical drilling methods. In addition, since laser ablation can directly engrave interior microstructures in one closed chip, glue smearing problems to damage molded microstructures possibly to occur during the chip sealing procedures can be avoided too.

Relevant damage features associated with femtosecond pulse laser and swift-ion irradiations on LiNbO3 crystals are comparatively discussed. Experiments described in this paper include irradiations with repetitive femtosecond-laser pulses (800 nm, 130 fs) and irradiation with O, F, Si, and Cl ions at energies in the range of 0.2-1 MeV/amu where electronic stopping power is dominant. Data are semiquantitatively discussed by using a two-step phenomenological scheme. The first step corresponds to massive electronic excitation either by photons (primarily three-photon absorption) or ions (via ion-electron collisions) leading to a dense electron-hole plasma. The second step involves the relaxation of the stored excitation energy causing bond breaking and defect generation. It is described at a phenomenological level within a unified thermal spike scheme previously developed to account for damage by swift ions. A key common feature for the two irradiation sources is a well-defined intrinsic threshold in the deposited energy density Uth required to initiate observable damage in a pristine crystal: Uth ≈1.3× 104 -2× 104 J/ cm3 for amorphization in the case of ions and Uth ≈7× 104 J/ cm3 for ablation in the case of laser pulses. The morphology of the heavily damaged regions (ion-induced tracks and laser-induced craters) generated above threshold and its evolution with the deposited energy are also comparatively discussed. The data show that damage in both types of experiments is cumulative and increases on successive irradiations. As a consequence, a certain incubation energy density has to be delivered either by the ions or laser photons in order to start observable damage under subthreshold conditions. The parallelism between the effects of laser pulses and ion impacts is well appreciated when they are described in terms of the ratio between the deposited energy density and the corresponding threshold value. © 2008 American Institute of Physics.