laser micromachining ,
laser materials chemistry ,
Plasma Enhanced CVD and CVD ,
laser materials interactions ,
Thin Films Technology and (Ultra-High) Vacuum Equipment ,
Focused Ion Beam Etching, Reactive Ion Etching of metal, semiconductor and dielectric materials
Profile Summary
• Extensive experience with applications of UV, visible and IR lasers – Excimer, Cu, CuBr, Sr, Ti:sapphire, Nd:YAG, Q-switch and SHG of Nd:YLF, Er:YAG, CO2 and Raman Lasers, IR Tunable Free Electron Lasers and Nd:YAG pumped OPO Lasers in Materials Processing, Materials Science and Chemistry. • Fundamental understanding and extensive experience in all Laser Materials Interactions, including laser micromachining, laser surface modification, high aspect laser drilling, PLD, laser materials chemistry and laser chemical etching applied to semiconductor, metal, ceramic and polymer materials. • Femtosecond laser machining of diamond, sapphire, Si, Ge, InP, polymers • Extensive Practice and deep understanding of following analytical techniques: SEM and EDX analysis, FTIR–transmittance, reflectance and ATR, UV-visible spectroscopy, XRD, Raman, XPS, FIB, AFM and SNOM, Mass Spectrometry, Profilometry. • Substantial Experience in Thin Films Technology and (Ultra-High) Vacuum Equipment. • Focused Ion Beam Etching, Reactive Ion Etching of metal, semiconductor and dielectric materials, • Wet Anisotropic Etching of Silicon for mold formation using organic and inorganic etchants. • E-Beam deposition, PECVD with microwave, RF & ICP plasma of semiconductor and dielectric materials. • Proficient in various computer programs and data analyses applications including but not limited to: LabVew Programing, Origin, Mathcad, CrystalMaker and Microsoft Office. • Plasma Enhanced CVD of nano and polycrystalline diamond, Diamond films brazing to Mo substrates • Electron Beam Lithography and Photolithography. • Extensive practice in design and construction of installations for Materials Processing, Optical Spectroscopy, Chemical Vapor Deposition and Mass Spectrometry; Optical and electrical measurement equipment including OSA, power meter, photodiodes, and current, voltage, and power meters. • Experience with microfluidic devices and soft lithography, pH sensors and biosensors with micron sizes
Publications (7)
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Purpose: It is hypothesized that 6.1 μm produced by a portable laser would be useful for incising tissue layers such as performing a retinectomy in detached retina with extensive anterior proliferative vitreoretinopathy.
Methods: An alexandrite laser system, which provides a high-intensity Q-switched pulse (780 nm, 50-100 ns duration, 10 Hz), is
wavelength-shifted by a two-stage stimulated Raman conversion process into the 6-7 μm range (Light Age, Inc.). Fresh cadaver porcine retinas were lased with 6.1 μm using a 200 μm diameter spot at 0.6 mJ after removal of the vitreous. Specimens were examined grossly and prepared for histological examination.
Results: The Raman-shifted alexandrite laser produced a smooth Gaussian profile. A narrow spectrum was produced at 6.1 μm. A full-thickness retinal incision with minimal thermal damage was obtained at a low energy level of 0.6 mJ in the retinas. However, the depth of the incision did vary from an incomplete incision to a full-thickness incision involving the underlying choroidal layer in
attached retinas. Conclusions: The 6.1 μm mid-infrared energy produced by a portable laser is capable of incising
detached retinas with minimal thermal damage.
An investigation of a strontium bromide vapor laser excited by a nanosecond pulsed longitudinal discharge is presented.
The optimal discharge conditions for laser oscillation on several Sr atom and ion lines are found. At multiline output an
average laser power of 2.4 W is obtained, more than 80 % of which is concentrated at the 6.45-μm Sr atom line.
Polymer light emitting diodes (PLEDs) have been fabricated in a vacuum environment by resonant infrared laser
ablation of the light emitting layer. The light emitting polymer used was poly[2-methoxy-5-(2-ethylhexyloxy)-
1,4-phenylenevinylene] (MEH-PPV) and was deposited into the device structure ITO/MEH-PPV/Al. Fourier
transform infrared (FTIR) spectroscopy confirmed that the laser-deposited polymer was not drastically altered by
the deposition process. Laser-fabricated devices displayed similar properties such as electroluminescence spectra
and IV characteristics as conventional spin-coated devices. The dependence of these device properties on laser
fluence was investigated, and showed no strong dependency. Peak emission wavelengths of electroluminescence
spectra were all within 10 nm of electroluminescence spectra of spin coated devices and showed only slight peak
broadening. These results are technologically important in that shadow mask technology can be incorporated
into this method to arbitrarily pattern substrates with light emitting polymers.
A gas discharge strontium vapor laser has been shown to operate with up to 90% of its light emitted at 6.45 μm. We have investigated the use of this laser as a potential stand-alone, tabletop alternative to the FEL for ablation of soft tissue. This custom-made laser currently delivers up to 2.4 watts of average power at 13 kHz pulse repetition rate (range 5-20 kHz). Despite a poor spatial beam profile the laser has been shown to ablate both water and soft tissue. However, current pulse energies (< 185 μJ) are insufficient for single pulse ablation even when focused to the smallest possible spot size (130 μm). Instead, the high pulse repetition rate causes the ablation to occur in a quasi CW manner. The dynamics of ablation studied by pump-probe (Schlieren) imaging and macroscopic white light imaging showed micro-explosions but at a rate well below the pulse repetition frequency. Histological analysis of ablation craters in bovine muscle exhibited significant collateral thermal damage, consistent with the high pulse frequency, thermal superposition and heat diffusion. Efforts to increase the pulse energy in order to achieve the threshold for pulse-to-pulse ablation are ongoing and will be discussed.
A sealed-off strontium-vapor laser for medical applications is examined. This is an integrated system that accommodates an excitation circuit, a laser cavity, and an active element. The active medium is excited by means of a modified Blumlein circuit. An unstable resonator of the telescopic type allows a near-diffraction-limited laser beam to be generated. Lasing is obtained in atomic strontium lines at λ=2.06, 2.2, 2.69, 2.92, 3.011, and 6.45 μm and in ionic strontium lines at λ=1.033 and 1.091 μm. We have studied experimentally the behavior of spectral distribution of the output power at varying power delivered to the discharge. It is found that 95% of laser radiation is concentrated in the line at λ=6.456 μm, which corresponds to a lasing power of ~ 2.5 W. Moreover, the time characteristics of lasing pulses are investigated. The radial inhomogeneity of the laser beam is examined. We have conducted lifetime testing of Sr-vapor active elements. The average output power exhibits a modest decrease (5%) within 300 h of a continuous operation. Notably, the pumping characteristics remain unchanged.
As laser micromachining is applied to ever smaller structures and more complex materials, the demand for greater control of the laser energy budget, in space and time, grows commensurately. Here we describe materials modification using picosecond resonant laser excitation in the mid-infrared spectral region to create spatially and temporally dense vibrational, rather than electronic, excitation. Examples include ablation of fused silica and machining of crystalline quartz; deposition of functionalized polymers on microstructures, and laser-directed transfer of proteins and nucleotides from a matrix of water ice. The experiments demonstrate that high spatial and temporal density of vibrational excitation can be achieved by ultrafast resonant infrared excitation of selected vibrational modes of these materials. In some cases, resonant infrared materials modification is far more successful than techniques based on ultraviolet excimer lasers. The laser used for most of the experiments was a tunable, high pulse-repetition frequency free-electron laser. However, a comparison of polymer deposition using a conventional nanosecond laser at a wavelength of 2.94 μm shows that the possibility exists for transferring the concept to conventional table-top devices. Mechanistic considerations nevertheless suggest that utlrashort pulses are likely to be more useful than longer pulses for many applications. A figure of merit is proposed for self-consistent comparisons of processing efficiency among different lasers.
We report studies on the efficiency of mid-infrared laser ablation of bovine cortical bone using a free-electron laser when the ablation zone is irrigated with chemically inert and biocompatible perfluorocarbon compounds. Bovine bone samples were cut into slices with thicknesses ranging from 0.2mm to 4.0 mm. At wavelengths of 2.94, 6.1 and 6.45 micrometers the water and collagen in the bone matrix absorb the laser radiation; the perfluorocarbons transmit light at all these wavelengths, albeit with drastically varying absorption coefficients. The perfluorocarbons also dissipate heat and acoustical stress, and, under optimal conditions, prevent carbonization of the bone. The ablation efficiency - as well as plasma and bubble formation, acoustic signals and carbonization - are critically dependent on the molecular weight of the perfluorocarbon compound and its thickness. The ablation efficiency was determined as a function of wavelength, scanning speed, number of scans, and perfluorocarbon species and thickness. The laser fluence was estimated to be in the range 35 J/cm2-70j/cm2 for all wavelengths; the scanning speed was varied over the range 40micrometers /s-2960 micrometers /s. The ablation rate was estimated from scanning electron microscopy to be 0.5 mm/s. This is higher than that reported for ns Er:YAG and Q- switched CO2 lasers. The morphology of the ablation cuts at 2.94micrometers suggests a possible role for nonlinear absorption in the bone.
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