Mark Dugan

Observation of fast time scale spectral diffusion in a low temperature glass: comparison of picosecond photon and stimulated echoes

Abstract Results of temperature-dependent two-pulse photon echo and three-pulse stimulated echo experiments on an organic dye (rhodamine 101) in a polymer glass (PMMA) are presented. Decay rates at a fixed temperature are shown to increase as the waiting time, T W (time between the second and third pulse) of the stimulated echo increases. This is due to spectral diffusion caused by structural relaxations of the host. At a fixed waiting time, decay rates follow a power law dependence on temperature which is characteristic of the glassy state. The data are analyzed by explicitly evaluating the stimulated echo correlation function for short T W .

Waveguide electro-optic modulator in fused silica fabricated by femtosecond laser direct writing and thermal poling

An integrated electro-optic waveguide modulator is demonstrated in bulk fused silica. A Mach-Zehnder interferometer waveguide structure is fabricated by direct writing with a femtosecond laser followed by thermal poling. A 20 degrees electro-optic phase shift is achieved at an operating wavelength of 1.55 microm with an applied voltage of 400 V and an interaction length of 25.6 mm, which correspond to an estimated effective electro-optic coefficient of 0.17 pm/V for the TE-polarized mode.

Dynamics in a low‐temperature glass: Fast generation and detection of optical holes

High‐resolution, fast optical hole‐burning results are reported for the amorphous system cresyl violet in ethanol glass at 1.3 K. Holes are burned and detected using a novel technique which allows precise detection of narrow (∼0.03 cm−1 ), shallow (∼1%) holes 10 μs to 50 ms after their generation. The technique is described in detail along with careful tests demonstrating the validity of its results. The hole width is observed to increase linearly with time when plotted against log time. Using the four time correlation function description of optical hole burning, the time‐dependent increase in hole width (spectral diffusion) is shown to arise from a broad distribution of fluctuation rates in the glass with the probability of having a fluctuation at rate R proportional to 1/R. The 10 μs to 50 ms data is combined with hole‐width data spanning the range 100 ms to 10 000 s and with two‐pulse picosecond photon echo data. The two‐pulse photon echo linewidth is calculated by extrapolating the fluctuation rate d...

Quasi-phase matched second-harmonic generation through thermal poling in femtosecond laser-written glass waveguides

Quasi-phase matched second-harmonic generation at 532 nm is demonstrated in a channel waveguide that is written in bulk fused silica using a femtosecond laser. The second-order nonlinear grating is fabricated using uniform thermal poling followed by periodic erasure inside an e-beam deposition system caused, by what we believe to be, x-rays. A SHG conversion efficiency of 2 x10(-5) %/W-cm(2) was obtained for a 1 cm long device, corresponding to an effective nonlinear coefficient of 0.0075 pm/V.

Optical microsystem for analyzing engine lubricants

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.

In-situ optical detection of mesoscale components in glass microfluidic channel with monolithic waveguide

Optical waveguides used as a local light source along a fluidic channel have proven to be an effective approach to detecting cells in the field of flow-cytometry. One challenge, however, has been a simple integration of optical waveguides with the fluidic channel. We employ the use of femtosecond laser-writing process to pattern a waveguide in the bulk of a fused-silica glass substrate housing a fluidic channel. We demonstrate an in-situ scheme for detecting sub-millimeter components based on such a monolithically fabricated device. By illuminating the waveguide and collecting the light signal past the channel, we detect opaque and transparent components between 300 - 500 μm in size, as each moves along the channel. Both an opaque square chip and a transparent bead attentuate the signal by more than 95% primarily due to reflection and refraction respectively. The signature of a transparent bead additionally shows attenuated peaks which we attribute to normal incidence of light from the waveguide. The projected sizes of the parts are determined with less than 1% uncertainty. We conclude that the femtosecond laser produced waveguides in fused-silica glass are a viable option for the detection of certain kinds of sub-millimeter components. This approach holds the prospects of fabricating complex three-dimensional networks of waveguides monolithically.

Investigation of femtosecond laser irradiation on fused silica

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.

Monolithic integration in fused silica: When fluidics, mechanics and optics meet in a single substrate

We show that locally altering fused silica with femtosecond laser irradiation forms the basis for a novel manufacturing technology platform to produce highly integrated microsystems. In contrast to many common approaches that rely on combining materials to achieve particular functions, our scheme utilizes a single piece of material, whose properties are locally modified using femtosecond laser irradiation. This microsystem fabrication method is not only particularly attractive for optofluidics instruments but also for optomechanical devices.

Towards a femtosecond laser micro-machined optofluidic device for distinguishing algae species

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.

All-optical, ultra-high accuracy displacement sensors with detection means

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.