We describe a non-invasive and non-contact viscosity measurement system using a compact optical fiber heterodyne interferometry. The proposed system consists of a fiber based pulse laser for surface acoustic wave (SAW) excitation and a lensed fiber for probing laser. When the pulsed laser illuminates onto the oil surface, the SAW is generated by photoacoustic effect and it propagates along the surface. The interference of probing laser reflected on the sample surface has the information of the surface movement. We can calculate the propagation velocity of SAW from the detected interference signal. The propagated SAW contains the information of liquid properties (viscosity and elasticity). For the preliminary measurements, an industrial engine oil and a polydimethylsiloxane (PDMS) are used. We can measure the viscosity of them without noncontact, successfully.
Microfluidics technology which deals with small liquid samples and reagents within micro-scale channels has been widely applied in various aspects of biological, chemical, and life-scientific research. For fabricating microfluidic devices, a silicon-based polymer, PDMS (Polydimethylsiloxane), is widely used in soft lithography, but it has several drawbacks for microfluidic applications. Glass has many advantages over PDMS due to its excellent optical, chemical, and mechanical properties. However, difficulties in fabrication of glass microfluidic devices that requires multiple skilled steps such as MEMS technology taking several hours to days, impedes broad application of glass based devices. Here, we demonstrate a rapid and optical prototyping of a glass microfluidic device by using femtosecond laser assisted selective etching (LASE) and femtosecond laser welding. A microfluidic droplet generator was fabricated as a demonstration of a microfluidic device using our proposed prototyping. The fabrication time of a single glass chip containing few centimeter long and complex-shaped microfluidic channels was drastically reduced in an hour with the proposed laser based rapid and simple glass micromachining and hermetic packaging technique.
A 1030 nm pulsed femtosecond laser has been use to induce modifications in silver containing glass namely femto-photo
luminescent glass (FPL) and Photo-thermo refractive glass (PTR). The 5W 10Mhz laser is focused at a depth of 200 μm
in the glass using a 0,52 NA objective. The output polarization of the laser is TM. The tailoring of the number of pulses,
pulse energy and repetition rate is achieve by acousto-optic filtering. The interaction resulted in the creation of stable
pipe-shaped silver clusters forming bellow refraction-limit 3D structures. Those nano-structures exhibit non-linear
properties such as SHG and THG as well as fluorescence. Due to multiphoton absorption, free electrons are created in
the central part of the beam, enabling the reduction of Ag<sup>+</sup> silver ions into Ag<sup>0</sup> and subsequently Ag<sub>m</sub><sup>X+</sup>. The cumulated
thermal effect of the pulses weakens the glass matrix allowing the diffusion of the Ag<sub>m</sub><sup>X+</sup>. The ion concentration gradient
creates a buried electric field enabling non-linear properties. Influences of polarization, dose and fluence on the nonlinear
properties are investigated. Our explanation of the causes of SHG and THG are validated by the accordance
between the theory and the measurement. Comparisons between theoretic model and our results showing accordance in
the limits of out 2D model are demonstrated using different incoming polarizations.
In recent years, a major interest in surface as well as bulk property modification of semiconductors using laser irradiation
has developed. A.Kar et al.  and E.Mazur et al.  have shown introduction and control of dopants by long-pulse
laser irradiation and increased absorption due to femtosecond irradiation respectively. With the development of mid-IR
sources, a new avenue of irradiation can be established in a spectral region where the semiconductor material is highly
transparent to the laser radiation. The characterization of the light-matter-interaction in this regime is of major interest.
We will present a study on GaAs and its property changes due to pulsed laser irradiation ranging from the visible to the
mid-IR region of the spectrum. Long-pulse as well as ultra-short pulse radiation is used to modify the material.
Parameters such as ablation threshold, radiation penetration depth and thermal diffusion will be discussed.
Femtosecond laser direct writing (FLDW) has been widely employed to create volumetric structures in transparent
materials that are applicable as various photonic devices such as active and passive waveguides, couplers, gratings,
and diffractive optical elements (DOEs). The advantages of fabrication of volumetric DOEs using FLDW include
not only the ability to produce embedded 3D structures but also a simple fabrication scheme, ease of customization,
and a clean process. DOE fabrication techniques using FLDW are presented as well as the characterization of laserwritten
DOEs by various methods such as diffraction efficiency measurement. Fresnel zone plates were fabricated in
oxide glasses using various femtosecond laser systems in high and low repetition rate regimes. The diffraction
efficiency as functions of fabrication parameters was measured to investigate the dependence on the different
fabrication parameters such as repetition rate and laser dose. Furthermore, several integration schemes of DOE with
other photonic structures are demonstrated for compact photonic device fabrication.
The ability to integrate micro-channels for fluid transport with optical elements is attractive for the development of
compact and portable chip-based sensors. Femtosecond Laser Direct Writing (FLDW) in transparent materials is a
powerful tool for the fabrication of such integrated devices. We demonstrate the use of FLDW to fabricate coupled
micro-fluidic channels and optical waveguides towards an integrated sensing device for molecular detection.
Waveguides were directly written into the host material and channels were formed by modifying the molecular structure
through FLDW followed by wet chemical etching. Multiple host materials including chalcogenide glasses for IR
detection are discussed.
Femtosecond laser direct writing was applied to fabricate 3D diffractive optical elements in oxide glass. Here we
report our initial results. We describe the consequences of fabricating Fresnel Zone Plates (FZPs) with various
femtosecond laser parameters. Single or multiple layers of laser written FZPs were produced in borosilicate glasses.
We are investigating the diffraction efficiencies as a function of laser and writing parameters such as pulse energy,
writing speed and repetition rate.
Optical coherence microscopy (OCM) is used to image femtosecond laser direct written buried structures created
within transparent media. Volumetric structures of optical damage and laser-induced refractive index change were
produced in fused silica and borosilicate glass, respectively. Noninvasive 3D imaging of the structures was
successfully demonstrated by a custom built OCM. High signal to noise ratio was obtained since the optical glasses
have high transparency at the probe wavelength centered at 800 nm.