Fused silica (a-SiO2) exposure to low-energy femtosecond laser pulses (below ablation threshold) introduces a local
increase of the HF etching rate. This property has been used to fabricate a variety of structures ranging from simple
fluidic channels to more complex optofluidics and optomechanical devices. In practice, the desire patterns are written by
contiguously stacking laser exposed regions, which defined the volume to be removed.. In previous work, we showed
that there was an optimum energy level for maximizing the efficiency of the etching process. Here, we focus on the
interaction between adjacent laser affected zones and its effects on the overall etching process. Experimentally, we
exposed fused silica specimens to patterns consisting of matrices of lines with varying density, under various laser
exposure conditions. Surprisingly, we show that for certain laser affected zone densities and pulse energies, the exposed
regions do not etch while their constitutive elements (i.e. the single laser affected zones) do. This paper describes our
recent experimental observations and proposes a qualitative model to explain these findings.
Flexures are mechanical elements used in micro- and precision-engineering to precisely guide the motion of micro-parts.
They consist of slender bodies that deform elastically upon the application of a force. Although counter-intuitive at first,
fused silica is an attractive material for flexure. Pending that the machining process does not introduce surface flaws that
would lead to catastrophic failure, the material has a theoretically high ultimate tensile strength of several GPa. We
report on high-aspect ratio fused silica flexures manufactured by femtosecond laser combined with chemical etching.
Notch-hinges with thickness as small as twenty microns and aspect ratios comparable to aspect ratios obtained by Deep-
Reactive-Ion-Etching (DRIE) were fabricated and tested under different loading conditions. Multiple fracture tests were
performed for various loading conditions and the cracks morphologies were analyzed using Scanning Electron
Microscopy. The manufactured elements show outstanding mechanical properties with flexural strengths largely
exceeding those obtained with other technologies and materials. Fused silica flexures offer a mean to combine integrated
optics with micro-mechanics in a single monolithic substrate. Waveguides and mechanical elements can be combined in
a monolithic devices opening new opportunities for integrated opto-mechatronics devices.
We demonstrate a small device with a microfluidic channel and an integrated waveguide that functions a compact
rudimentary tool for the detection, real-time monitoring, and potentially classification of algae. In order to reduce
parasitic noise the micro-device used a curved subsurface optical waveguide to illuminate particles transiting through a
microfluidic channel. The changes in the transmitted signal are monitored using a quadrant-cell photo-detector. The
signals wavelets from the different quadrants are used to qualitatively distinguish different families of algae. Additional
information, such as flow direction, is also provided. The channel and waveguide are fabricated out of a monolithic
fused-silica substrate using a femtosecond laser-writing process combined with chemical etching. This proof-of-concept
device paves the way for more elaborate femtosecond laser-based optofluidic micro-instruments incorporating
waveguide network designed for the real-time analysis of cells and microorganisms in the field.
We present some small optical instruments fabricated with femtosecond laser pulses. These instruments, made from
monolithic fused silica substrates, incorporate an extensive collection of optical and micro-mechanical elements. A
single manufacturing step was used to define both the optical and the mechanical features. This approach dramatically
simplifies overall fabrication and eliminates alignment issues associated with sequential fabrication processes. Potential
applications and technical challenges are reviewed.
We demonstrate a small device with a microfluidic channel and an integrated waveguide as a compact rudimentary tool
for the detection, real-time monitoring, and potentially classification of algae. In order to reduce parasitic noise the
micro-device used a curved subsurface optical waveguide to illuminate particles transiting through a microfluidic
channel. The changes in the transmitted signal are monitored using a quadrant-cell photo-detector. The signals wavelets
from the different quadrants are used to qualitatively distinguish different families of algae. Additional information, such
as flow direction, is also provided. The channel and waveguide are fabricated out of a monolithic fused-silica substrate
using a femtosecond laser-writing process combined with chemical etching. This proof-of-concept device paves the way
for more elaborate femtosecond laser-based optofluidic micro-instruments incorporating waveguide network designed
for the real-time analysis of cells and microorganisms in the field.
Low-energy femtosecond laser pulses (typically in the tenth of nJ per pulse regimes at 250kHz) focused into fused silica
substrates induce various modifications in the material properties of the base material, including a localized increase of
the refractive index. Related sub-microns periodic structures found in the laser-exposed regions have also been recently
described by several authors. The characterization of the laser-affected zones is particularly challenging due to their
small sizes - typically micron or sub-micron. Experimental methods previously reported have either limited spatial
resolution or require additional material processing to reveal the zone of interest, leaving open questions related to the
influence of the processing itself. Using an Atomic Force Microscope equipped with a thermal probe, we recently
published that low-energy femtosecond laser pulses leave thermal conductivity change footprints. The thermal footprints
match very well the zone where a higher refractive index is observed. This novel analytical method does not require any
processing of the surface prior to the observation and yields high-quality, sub-micron resolution, maps of the laser
affected zones. Furthermore, it also opens new interesting and fundamental questions on the effect of femtosecond laser
irradiation on fused silica. In this paper, we report on systematic observations made on fused silica specimens exposed to
various pulse energies under different polarization conditions. We analyze and discuss the effect of the laser exposure on
the thermal properties of the fused silica substrate.
Femtosecond laser irradiation has various noticeable effects on fused silica. It can locally increase the index of refraction and modify the material chemical selectivity. Regions that have been exposed to the laser are etched hundred fold faster than unexposed regions. These effects are of practical importance from an application point-of-view and open new opportunities for the development of integrated photonics devices that combine structural and optical functions.
Various observations reported in the literature indicate that those effects are potentially related to a combination of both structural changes and the presence of internal stress. In this paper, we present further investigations on the effect of femtosecond laser irradiation on fused silica substrate (a-SiO2). In particular, we use nanoindentation and holography-based birefringence measurements, coupled with direct SEM observations on chemically etched specimens to characterize the effect of various laser parameters such as power, scanning speed and irradiation pattern. We show evidence of an interface between two different etching regimes that may be related to the presence of two different material phases induced by the laser irradiation.
We present a high-accuracy force or displacement sensor made only of fused silica. This device merges integrated optics and micro-mechanics in a monolithic substrate. It differs from previous micro force sensor works in that the measured variable is acquired optically, rather than electrically. The device was manufactured using a combination of femtosecond laser pulses and chemical etching. A single manufacturing step was used to define both the optical and the mechanical features. This approach dramatically simplifies the overall fabrication and eliminates alignment issues associated with sequential fabrication processes. Our displacement sensor is composed of a mobile platform and a fixed frame. These components are linked together through sixteen high-aspect ratio double-compound flexures. This design firmly restrains the motion of the platform along a single axis. The range of motion exceeds 1-millimeter. Integrated waveguides are used to measure the displacement of the displacement with accuracy better than 50-nm.
This paper reports a novel approach based on femtosecond laser processing to design micro-mechanical sensors such as force and displacement sensors. The basic concept is to combine integrated optics and mechanical functions in a single piece of glass. It differs from previous micro displacement sensor works in that the measured variable is optical rather than electrically based (strain-resistive, piezo-electric, etc.). Furthermore, a single process is used to define both the optical and the mechanical features. This significantly simplifies the overall fabrication and eliminates alignment issues associated with sequential fabrication processes.
It is possible to dramatically improve the performance, reliability, and maintainability of vehicles and other similarly complex equipment if improved sensing and diagnostics systems are available. Each year military and commercial maintenance personnel unnecessarily replace, at scheduled intervals, significant amounts of lubricant fluids in vehicles, weapon systems, and supporting equipment. Personnel draw samples of fluids and send them to test labs for analysis to determine if replacement is necessary. Systematic use of either on-board (embedded) lubricant quality analysis capabilities will save millions of dollars each year in avoided fluid changes, saved labor, prevented damage to mechanical components while providing associated environmental benefits. This paper discusses the design, the manufacturing, and the evaluation of robust optical sensors designed to monitor the condition of industrial fluids. The sensors reported are manufactured from bulk fused silica substrates. They incorporate three-dimensional micro fluidic circuitry side-by-side with three-dimensional wave guided optical networks. The manufacturing of the optical waveguides are completed using a direct-write process based on the use of femtosecond laser pulses to locally alter the structure of the glass substrate at the nano-level. The microfluidic circuitry is produced using the same femtosecond laser based process, followed by an anisotropic wet chemical etching step. Data will be presented regarding the use of these sensors to monitor the quality of engine oil and possibly some other vehicle lubricants such as hydraulic oil.
The index of refraction of most glasses can be permanently changed by exposure to femtosecond laser pulses. This effect allows for the fabrication of various two-dimensional or three-dimensional light guiding structures. Passive and active optical devices have been manufactured using this femtosecond direct-write technique. A closely related technique has recently been demonstrated to manufacture three-dimensional microfluidic networks.
We describe recent work at Translume and RPI in femtosecond direct write to produce devices which incorporate on a single glass chip optical network with microfluidic network.
Conventional laser machining is based on continuous-wave or long-pulse lasers. With these lasers, thermal diffusion limits the accuracy and the reproducibility of the machining process. Laser-matter interaction is fundamentally different in the ultrafast (femtosecond) regime. This discovery has opened the way for generalized fine laser micromachining.
We describe our work on the amplification of short pulses in tunable solid state materials; specifically alexandrite and Ti:sapphire.
Our goal is to amplify femtosecond range pulses to the joule level in a table top size laser. We will describe our results which show
that such a laser is now feasible.
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