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Due to its hardness, strength, and transparency, sapphire is an attractive material for the construction of microfluidic devices intended for high-pressure applications, but its physiochemical properties resist traditional microfabrication and bonding techniques. Here a femtosecond pulsed laser was used to directly machine fluidic channels within sapphire substrates and to form bonds between machined and flat sapphire windows, resulting in the creation of sealed microfluidic devices. Sapphire-sapphire bond strength was determined by destructive mechanical testing, and the integrity of the bond was verified by the capillary filling of the channel with air and ethanol. This combination of optical micromachining and bonding establishes a fully integrated approach to the fabrication of sapphire-based microfluidic systems.

Glass micromodels have been extensively used to simulate and investigate crude oil, brine, and surface interactions due to their homogeneous wettability, rigidity, and ability to precisely capture a reservoir’s areal heterogeneity. Most micromodels are fabricated via two-dimensional patterning, implying that feature depths are constant despite varying width, which sub-optimally describes a three-dimensional porous architecture. We have successfully fabricated micromodels with arbitrary triangular cross sections via femtosecond pulsed laser direct writing resulting in depth-dependent channel width. As such, we have achieved arbitrary geometric control over device fabrication and thus a more accurate recapitulation of a geological porous media. With this fabrication technique, we are now able to directly observe pore-level, depth-dependent multiphase flow phenomena. This platform was used to study the low salinity effect (LSE) by simulating waterflooding processes using various brine solutions that differ in cation type and salinity. Patterned pore-throat structures were created to investigate displacement behavior during waterflooding. Real-time monitoring of the displacement processes, combined with a comparison of the brine chemistry before and after waterflooding provides an insight into realistic interactions occurring between crude oil and brine. The results indicate that produced emulsions were prone to coalesce in the presence of lower salinity brine. Combined with previous work, the LSE was interpreted as favored coalescence and resisted breakup that resulting in a more continuous aqueous phase during waterflooding therefore improving the displacement efficiency.

A watt level, 10-kz repetition rate chirped pulse amplification system that has an integrated simultaneous spatial and temporal focusing (SSTF) processing system is demonstrated for the first time. SSTF significantly reduces nonlinear effects normally detrimental to beam control enabling the use of a low numerical aperture focus to quickly treat optically transparent materials over a large area. The integrated SSTF system has improved efficiency compared to previously reported SSTF designs, which combined with the high-repetition rate of the laser, further optimizes its capability to provide rapid, large volume processing.

Proper alignment is critical to obtain the desired performance from focused spatially chirped beams, for example in simultaneous spatial and temporal focusing (SSTF). We present a simple technique for inspecting the beam paths and focusing conditions for the spectral components of a broadband beam. We spectrally resolve the light transmitted past a knife edge as it was scanned across the beam at several axial positions. The measurement yields information about spot size, M2, and the propagation paths of different frequency components. We also present calculations to illustrate the effects of defocus aberration on SSTF beams.

Simultaneous spatially and temporally focussing (SSTF) of ultrashort pulses allows for an unprecedented control of the intensity distribution of light. It has therefore a great potential for widespread applications ranging from nonlinear microscopy, ophthalmology to micro-machining. SSTF also allows to overcome many bottlenecks of ultrashort pulse micro-machining, especially non-linear effects like filamentation and self-focussing. Here, we describe and demonstrate in detail how SSTF offers an additional degree of freedom for shaping the focal volume. In order to obtain a SSTF beam, the output of an ultrafast laser is usually split by a grating into an array of copies of the original beam, which we refer to as beamlets. The ratio of the beamlet array width to the width of the invidual beamlet is the beam aspect ratio. The focal volume of the SSTF beam can now be tailored transversally by shaping the cross-section of the beamlets and axially by choosing the right beam aspect ratio. We will discuss the requirements of the setup for a successful implementation of this approach: Firstly, the group velocity dispersion and the third order dispersion have to be compensated in order to obtain a high axial confinement. Secondly, the beamlet size and their orientation should not vary too much spectrally. Thirdly, beamlet and SSTF focus should match. We will hence demonstrate how SSTF allows to inscribe tailored three-dimensional structures with fine control over their aspect ratio. We also show how the SSTF focus can be adapted for various glasses and crystals.

Through the development of simultaneous spatial and temporal focusing, platforms that can ablate tissue with excellent axial precision, and perform high-speed multiphoton imaging are converging. Recent developments in these platforms are presented.

A Ti:Al2O3 chirped-pulse amplification system is used to simultaneously image and machine. By combining simultaneous spatial and temporal focusing (SSTF) with spatial frequency modulation for imaging (SPIFI), we are able to decouple the imaging and cutting beams to attain a resolution and a field-of-view that is independent of the cutting beam, while maintaining single-element detection. This setup allows for real-time feedback with the potential for simultaneous nonlinear imaging and imaging through scattering media. The novel SSTF machining platform uses refractive optics that, in general, are prohibitive for energetic, amplified pulses that might otherwise compromise the integrity of the focus as a result of nonlinear effects.

We demonstrate a method for encoding spatial information across a line cursor using chirped amplitude modulation for application to one-dimensional multiphoton microscopy using a single-element detector. Resolution, along with imaging speed and quality, will be discussed.

We analyze the structure of space-time focusing of spatially-chirped pulses using a technique where each frequency component of the beam follows its own Gaussian beamlet that in turn travels as a ray through the system. The approach leads to analytic expressions for the axially-varying pulse duration, pulse-front tilt, and the longitudinal intensity profile. We find that an important contribution to the intensity localization obtained with spatial-chirp focusing arises from the evolution of the geometric phase of the beamlets.

We demonstrate, for the first time, a multimodal multiphoton microscope using chirped intensity modulation to construct line images from a single element detector.

Space-time focusing of spatially-chirped Ti:Sapphire laser pulses is used to generate a plasma in air axially localized to 28× less than the confocal parameter, suppressing filamentation on the way to the focus.

Space-time focusing of spatially-chirped Ti:Sapphire laser pulses is used to generate a plasma in air axially localized to 28x less than the confocal parameter, suppressing filamentation on the way to the focus.

Simultaneous spatial and temporal focusing provides precise control of the pulse front tilt necessary for anisotropic writing and maintains this behavior over a large range of focal positions and at low numerical aperture and fluence.

This report focuses on the design, application, and testing of custom beamsplitter and anti-reflection coatings for use in the Magdalena Ridge Observatory Interferometer (MROI) beam combiners. The coatings were designed in collaboration with Optical Surface Technologies, and the University of Cambridge. The fringe tracker and science combiners will operate across the J, H, and K bands. The coatings were designed to achieve three optical characteristics critical to optical interferometry: 1) minimized stress of the substrate (leading to induced wavefront errors), 2) high throughput, and 3) high visibilities in broadband unpolarized light. The AR coating has mean reflection losses of less than 0.5%. Beamsplitter coatings experienced visibility losses less than 1% due to group delay dispersion and s and p phase differences.

We report on the design and performance of a 6-way multi-wavelength beam combining instrument for the MRO Interferometer, allowing for fringe measurements at any of the J/H/K near-infrared bands at switchable spectral resolution with high sensitivity. Three preliminary designs for the instrument are presented and compared. The results of an ongoing evaluation performed on the performance, costs, and risks of each designs are analysed. Signal-to-noise analyses confirm in particular the utility of one of the design at magnitudes as faint as K=13.

We report on the opto-mechanical design of the MROI fringe tracker. This instrument, currently under development in collaboration with the University of Cambridge, will be a dedicated fringe tracking beam combiner and spectrographs. I will utilize the "Y" geometry of the array to stabilize fringes on shorter "nearest neighbor" baselines, and thus allow for increased integration times on the longer baselines and the buildup of signal to noise. The beam combiner has been designed to accommodate light from a maximum of ten telescopes (three in each array arm, one at the "Y" vertex), but can operate with fewer without having to change the overall layout. A single spectrograph will multiplex up to five nearest neighbor combinations onto a single detector. Identical spectrographs are located at opposite sides of the combiner outputs to simultaneously sample combination pairs that are radians out of phase with respect to one another. Keywords: MROI, interferometry, fringe tracking, baseline bootstrapping, pupil plane combination

Raman spectroscopy is the workhorse for label-free analysis of molecules. Here, we show that dense self-organized networks of nanoparticles produced during femtosecond laser can lead to a strong Raman enhancement effect.

Femtosecond laser exposure of fused silica in the nonablative regime can lead to various localized bulk modifications of the material structure. In this paper, we show that these laser-induced modifications can be used to tune silica thermal expansion properties permanently. In particular, we demonstrate that a given exposer regime leads to lower thermal expansion than the bulk, while other exposure conditions yield the opposite results. This remarkable property enables the possibility to engineer a given thermal expansion behavior by selectively exposing a material volume to a femtosecond laser beam. This finding opens up opportunities for a variety of integrated precision instruments and optical devices for which inertness to thermal fluctuations is essential.

In the non-ablative regime, femtosecond laser pulse duration is known to affect the nature of the modification induced in the microstructure of fused silica. It has been demonstrated than below 200 fs, two different regimes are found, one at low energy, leading to bulk densification while the second one – for higher energy, leading to self-organized structure - nicknamed nanogratings - that induce a net and localized volume expansion of the material. The first regime is particularly interesting for waveguides fabrication, although, so far, the reported refractive index gain remains modest, typically within 10-3 relative net increase that limits the level of compactness for photonics circuits making use of it. Here, we investigate further how shorter pulses, i.e. in the sub-50 fs range, can increase the level of densification and in turn, the net refractive index gain, and possibly lead to an improve process for photonics device fabrication. First results show that indeed, higher level of densification can be obtained, level that we quantify, and that can be further correlated to a net increase of refractive index.

Varying microfluidic channel cross-sectional geometry can dramatically alter fluid flow behavior, particularly for capillary-driven flow. Most fabrication techniques, however, are planar and therefore incapable of providing depth-dependent variations in width. We introduce an ultrafast laser ablation technique that enables the fabrication of microchannels with arbitrary triangular cross sectional geometry. Triangular channels were fabricated with widths ranging from 45 to 116 mu m and aspect ratios between 0.7 and 1.9. This experimental platform was utilized to observe two-phase flow and evaluate the capillary pressures required to initiate flow within triangular capillaries. Applying Mayer, Stowe and Princen (MS-P) theory, critical drainage capillary pressures were predicted for varying cross sections and compared to experimental observations. Results indicate the capability to predict capillary pressures inside triangular channels with perfectly water wet surfaces, providing the first instance of experimental validation of the theory for arbitrary triangular cross sections. This work was extended to intermediate wet conditions, which provides an insight into the prediction of capillary pressure under more realistic conditions. The fabrication techniques and validation of predictive frameworks presented here provide an approach to microfluidic experimental design that will impact a wide range of fundamental and applied technology areas. (C) 2017 Elsevier Inc. All rights reserved.

Raman spectroscopy is the workhorse for label-free analysis of molecules. It relies on the inelastic scattering of incoming monochromatic light impinging molecules of interest. This effect leads to a very weak emission of light spectrum that provides a signature of the molecules being observed. Considerable efforts have been made over the last decades, in particular with the development of Surface Enhanced Raman Spectroscopy (SERS), to enhance the intensity of the emitted signal so that ultimately, traces of molecules can be detected. Here, we show that dense self-organized networks of quasi-monodisperse nanoparticles redepositing during femtosecond laser ablation of trenches in fused silica can lead to a significant field enhancement effect, enabling the Raman detection of a single-molecule layer deposited on the surface (so called monolayer). Unlike previously reported for SERS experiments, here, there is no metal layer promoting plasmonics effects causing localized field enhancement. The method for producing SERS substrates is therefore quite straightforward and low cost. (C) 2017 Optical Society of America