Currently, high throughput manufacture of Lab-on-a-chip devices integrated with both microoptics and microfluidics faces serious challenges, including assembly and packaging. Because of their different physical properties and functions, the optical and the fluidic elements are often first separately fabricated on different substrates, and then assembled into a single Lab-on-a-chip device. The alignment between the microoptical and microfluidic components requires micron-scale precision. To overcome this difficulty, we recently developed a novel laser microfabrication technique to form 3D hollow structures buried in a photosensitive glass - Foturan. The formation of both the optical and the fluidic structures were completed in a unified fabrication process. The technique is based on femtosecond laser direct writing followed by post-baking and successive chemical etching, completely eliminating the assembling procedures such as alignment, fixation, stacking, and bonding that are inherent in traditional 3D microprocessing techniques. In this paper, we describe the fabrication of a broad variety of hollow structures in Foturan glass, and the integration of these structures to build functional micro-devices. Furthermore, we will discuss how to control the fabrication resolution in three dimensions by developing novel beam focusing schemes to generate isotropic focal spot shapes inside the transparent materials.

When femtosecond laser pulses are tightly focused into a transparent material, the intensity in the focal volume is high enough to induce permanent structural modifications. Using these permanent structural modifications, one can micromachine structures inside the bulk of a transparent material in three-dimensions. I present the fabrication of photonic devices in transparent materials, including waveguides, couplers, diffractive lenses, and microfluidic channels in silica glass and PMMA. Applications of femtosecond laser micromachining include the joining of glass substrates by localized melting and resolidification.

At energy level below the ablation threshold, femtosecond-laser irradiation of Fused Silica (a-SiO₂) can induce significant changes in the material properties: the refractive index and the chemical etching susceptibility can both be significantly increased. Using these effects one can scan a femtosecond laser beam through the substrate volume in order to create three-dimensional patterns with tailored material properties. Based on this approach, optical elements such as waveguides can be embedded in glass substrates. The elements can be provided with various functionalities such as for instance fluidic channels or micro-mechanical elements. In this paper, we show that femtosecond laser irradiation applied to Fused Silica (a-SiO₂) defines a novel technology platform for highly integrated all-optical microsystems. In contrast to the common approaches that rely on combining materials to achieve particular functions, our technology utilizes a single piece of material, whose properties are locally functionalized through femtosecond laser irradiation. This leads to a new micro-systems design paradigm, whose potential is illustrated with a few examples in this paper.

The mechanism of three-dimensional (3D) laser micro-structuring of dielectrics (resists, polymers, glasses, and crystals) by the direct laser writing is discussed. Overview of a light-matter interaction of a tightly-focused femtosecond pulse with dielectrics is presented. The void formation is demonstrated inside silica glass by a single picosecond pulse. Peculiarities of tight focusing and an axial superposition of two co-propagating pulses at the focus are revealed by numerical simulations. Potential of the fabricated 3D patterns in micro-photonics, micro-fluidics, and sensor applications is discussed.

Focused infrared femtosecond laser pulses (wavelength ~800 nm, emission pulse duration 100 fs) were employed to fabricate optoelectronic devices such as waveguides, micro-gratings and laser active centers in LiF crystals. F₂ color centers of about 2x10¹⁸ cm^-3 and refractive index change of about 1% at 633 nm were induced by the fs-laser irradiation. This technique was applied to fabricate a distributed-feedback (DFB) F₂ color center laser structure inside LiF single crystal. The LiF DFB laser exhibited laser oscillation at 707 nm at room temperature. The slope efficiency of ~10% and beam divergence of ~20 mrad were achieved.

The power handling capability of optical components is still one of the most important limitations for the further improvement of ultra-short pulse lasers in respect of average power and pulse energy. Laser-induced damage of functional dielectric coatings on laser crystals, pockels cells, out-coupling polarizers and compressor gratings is severely inhibiting the wide dispersion of ultra-short pulse laser systems especially in industrial production environments. Since the underlying physical causes for laser-induced damage with ultra-short pulses are distinctly differing from those in the nanosecond time scale, novel approaches must be found for an unambiguous improvement in damage resistance of optical coatings. In previous investigations, the band-gap of the coating material and the maximum field strength in the layer stack were identified as most important influences on the laser-induced damage with ultra-short pulses. Furthermore, a significant nonlinear increase of absorptance in dielectric coatings was found to be strongly related to the band-gap of the material. These effects were traced back to the multi-photon and avalanche-ionization as driving mechanisms for producing a critical conduction band population. In the current investigations, numerous model layer systems were investigated concerning laser-induced damage and non-linear absorptance. Adapting the ion beam sputtering coating process for achieving co-deposition of high and low index materials, coatings with continuously tunable refractive indices were produced. The results of the experiments exhibit a strong correlation of the damage threshold to the controllable shifting band-gaps of the coating materials.

Submicron-sized voids and void channels can be generated in a solid transparent polymer by using a tightly focused femtosecond laser induced micro-explosion method. By stacking the voids and void channels layer by layer and periodically, we can fabricate various three-dimensional (3D) photonic crystals of woodpile, face-centred-cubic, body-centred-cubic, and diamond lattice structures. The photonic bandgap effects and the defect generation in the photonic crystals have been revealed.

Acoustic phenomena during nanochannel machining by fs laser pulses are found to have an unexpected strong influence on the machining efficiency. Analysis of acoustic nodes that strongly limit machining efficiency allows strategies to be identified for fabrication of high aspect ratio channels. Based on an analytic solution for node formation, it is found that increasing the speed of acoustic transmission can produce a two-fold increase in the length of the channels; this can be accomplished by maximizing the mole fraction of hydrogen in the gas phase. The model is further reinforced by the effects of varying pressure.

Sub-80nm, sub-wavelength multiphoton nanoprocessing of silicon wafers as well as 3D maskless lithography by two two-photon polymerization in combination with five-dimensional (x,y,z, λ, τ) multiphoton analysis have been performed with the compact near infrared MHz femtosecond laser galvoscanning microscope FemtoCut (JenLab GmbH) as well as a modified ZEISS LSM510-NLO system. Laser excitation radiation was provided by a tuneable turnkey, one-box Chameleon as well as a MaiTai Ti:sapphire laser oscillator. Nanostructuring of silicon wafers with oil immersion objectives was based on NIR laser-induced periodic surface structures (LIPPS) likely due to selforganization processes. For the first time, periodic 70nm nanogrooves have been generated in wafers which is one order below the 800 nm laser wavelength by multiphoton phenomena at TW/cm² transient intensities and low sub-3nJ pulse energies. Three-dimensional two-photon polymerization in SU-8 photoresists at GW/cm² allowed rapid prototyping with sub-200nm precision. The same intensities have been used to image endogenous and exogenous fluorophores in a variety of materials for target finding and the evaluation of the nanoprocessing procedures.

Since the beginning of the 90's, Titanium Sapphire has become the crystal of choice for the development of ultrashort laser system producing very short and powerful pulses using the Chirped Pulse Amplification technique. In parallel to these developments leading to commercial products, new laser crystals have been studied in order to reach directly other wavelength range and to overcome the need to develop cw or pulsed green laser to pump the Titanium Sapphire crystal. In order to be able to directly pump the crystals with very efficient and high power semiconductor laser, new crystals doped with ytterbium ions have been developed. Actually, in the field of femtosecond lasers, an intense interest has been shown for ytterbium-doped laser-crystals. These crystals are now well-known to be particularly suitable for very efficient, directly-diode-pumped, solid state femtosecond oscillators. However, it has been shown that the spectral properties of the Yb³⁺ dopant strongly depend on the matrix host and a lot of works have been done to find the "ideal" matrix allowing both ultrashort-pulsed and high-power lasers. Firstly, in order to take advantage of the very high-power laser diodes available to pump Yb-doped materials, ideal crystals need to be able to hold high power pumping; so high thermal conductivity is required (\>5W/m/K, typically). Secondly, to generate very short pulses (<100 fs) ideal crystals have to demonstrate very broad and smooth spectra. Among the numerous Yb-doped crystals already studied, many failed with one of these two contradictory criteria (contradictory because broad spectra are often synonymous of high disorder in the host lattice and the good thermal conductivity requires an ordered matrix to allow good propagation of phonons). In this paper, we are relating the performance of a new Yb-doped crystal: Yb:CaGdAlO4 (Yb:CALGO) and how it takes place in this quest of "ideal" crystal. Actually, this very new crystal allowed, to our best knowledge, the shorter pulses ever produced with an Yb-doped crystal with the production of 47 fs pulses. Moreover, compared to other crystals allowing the production of sub-100 fs pulses such as Yb:GdCOB, Yb:BOYS and Yb:KGW, the atypical CALGO shows a thermal conductivity of 6.5W/m/K.

High energy femtosecond oscillators at high pulse repetition rate have a great potential for many applications such as micro- and nano-machining and structuring, waveguide writing in dielectric media, or nonlinear frequency conversion. Up to now most femtosecond oscillators operating at pulse repetition rates higher than 1 MHz were limited at pulse energies of typically a few tens of nanoJoules. We demonstrate a directly diode-pumped Yb:KYW laser oscillator delivering pulse energies up to 1 μJ and pulse durations down to 430 fs, thus pulse peak powers exceeding the MW level. The pulse repetition rate is 9 MHz and the average power is on the 10-W-level. The laser setup is compact and fits in a 60 x 40 cm footprint. We externally compressed the pulse duration of this laser down to about 60fs by focusing the laser into a large mode area micro-structured fiber followed by a compressor module containing a pair of parallel aligned dispersive mirrors. The good coupling efficiency and the high-reflecting dispersive mirrors resulted in an overall compressor transmission of 80%. For a maximum injected pulse energy of 0.53 μJ we obtained up to 0.42 μJ pulse energy after the compressor which corresponds to a peak power of 7 MW.

Defence Research & Development Canada (DRDC) has recently acquired a Terawatt laser system that will be mounted in a portable container. A class 100,000 clean room will be inserted in the container to maintain the ideal conditions for the laser operation. The compact laser system stands on a 1.25m x 2.5m optical table. The pulse energy at the output of the compressor is higher than 250 mJ and the pulse width output beam lower than 50 fs resulting in a peak power greater than 5 TW. Although the laser system is portable which allows its deployment for test fields on multi-kilometer ranges, a special building will be constructed to efficiently use its capabilities. While the container will seat inside a garage, it will be possible to steer the laser beam toward a well confined 200 m exterior range, or toward a class 100,000 laboratory. The primary objectives of the use of this laser are to study the beam filamentation and the generation of high energy THz waves.

In this paper we demonstrate how Holey Fibre (HF) technology can positively impact the field of materials processing and fabrication, specifically Direct Write (DW). DW is the large scale, patterned deposition of functional materials onto both flat and conformal surfaces. Currently, DW techniques involve thermal post-processing whereby the entire structure is enclosed inside an oven, so limiting the DW technique to small, heat resistant surfaces. Selectively laser curing the ink would allow the ink to be brought up to the required temperature without heating the surrounding substrate material. In addition the ability to trim components would allow miniature circuits to be written and devices to be tuned by changing the capacitance or resistance. HF technology enables in-situ curing and trimming of direct write components using the same rig and length of fibre. HF's with mode areas in excess of 450μm² can be routinely fabricated allowing high power transmission whilst retaining the high beam quality of the radiation source. We will present results of curing and trimming trials which demonstrate that HF's provide a distinct advantage over standard multimode fibres by allowing both curing and machining to be achieved through a single delivery fibre.

We present programmable focal spot shaping of amplified femtosecond laser pulses by use of an optically addressed non-pixellated liquid crystal light valve. This extra-cavity phase filtering method is set-up in the frame of femtosecond micromachining processes. Various focal spot shapes are demonstrated together with drilling and marking results in metals and dielectrics. Photowriting of waveguides in bulk fused silica is also presented.

We investigated femtosecond pump-repump depletion excitation in biological fluorescent molecules (tryptophan and flavins) in solutions and in organic fluorescent interferents such as polycyclic hydrocarbons (naphthalene, diesel fuel). If the repump pulse induces in both flavins and Trp a depletion of the excited state, populated by the pump pulse, which leads to a drastic decrease of the fluorescence, such mechanism is ineffective in organic fluorescent interferents. The repump induced depletion is still observed for bacteria containing solutions. This opens interesting perspectives to discriminate biological from non-biological fluorescent particles in air.