Plasmonic biosensing is an optical technique that based on refractive index change when the target molecules interact with the sensing surface. Main plasmonic material used in this type of biosensors is gold. Our work is dedicated to design a novel sensing SPR chip with vanadium dioxide (VO2) nanolayer, known for its unique insulator-to-metal phase transition in the near-infrared region. VO2 thin film is deposited using Cross-Beam Pulsed Laser Deposition (CB-PLD) method and gold layer deposition is performed by sputtering. By employing the VO2 nanolayer, we create a highly responsive biosensing interface (with a much-improved sensitivity and also a wide dynamic measurement range). The VO2 layer's ability to modulate the refractive index enables precise control of the excited plasmon resonance. This interaction results in enhancing sensitivity and the capability to detect low-concentration analytes with high accuracy.
A novel optical ridge waveguide using calcium barium niobate (CBN) with a high electro-optic coefficient on silicon substrate is proposed for the design and realization of the next-generation hybrid modulators with short length and low driving voltage. To overcome the etching difficulty of CBN, the design of a waveguide, including an elevated CBN layer based on etched silicon dioxide, is presented. Fabrication of a thick 2.5-µm CBN layer is performed using pulsed laser deposition. Deposited silicon dioxide on the sides and top of the CBN reduces the waveguide loss as low as 3.44 dB/cm, measured using a cutback method. Good agreement between the mode profiles of the simulation and measurement is obtained.
Laser-Induced Breakdown Spectroscopy (LIBS) technique combined with Laser-Induced Fluorescence (LIF) is known
to be a high sensitivity and high selectivity analytical technique. Although sub-ppm limits of detection (LoD) have
already been demonstrated, there is still a constant and urgent need to reach lower LoDs. Here, we report results obtained
for the detection of lead trace in brass samples. The plasma was produced by a Q-switched Nd:YAG laser at 1064 nm
and then re-excited by a nanosecond optical parametric oscillator (OPO) laser tuned at 283.31 nm. Emission from Pb
atoms was then observed at 405.78 nm. The experiments were performed in air at atmospheric pressure. We found out
that the optimal conditions were obtained for an ablation fluence of 2-3 J/cm2 and inter-pulse delay of 8-10 μs. Also,
excitation energy of about 200 μJ was required to maximize the Pb(I) 405.78 nm emission. Using the LIBS-LIFS
technique, the LoD was estimated to be about 180 ppb over 100 laser shots, which corresponds to an improvement of
about two orders of magnitude with that obtained using conventional LIBS.
Based on the principle of the Integrated Optical Spectrometer (IOSPEC), a waveguide-based, longwave infrared (LWIR) dispersive spectrometer with multiple input slits for Hadamard spectroscopy was designed and built intended for passive standoff chemical agent detection in 8 to 12μm spectral range. This prototype unit equips with a three-inch input telescope providing a field-of-view of 1.2 degrees, a 16-microslit array (each slit 60 μm by 1.8 mm) module for Hadamard binary coding, a 2-mm core ZnS/ZnSe/ZnS slab waveguide with a 2 by 2 mm2 optical input and micro-machined integrated optical output condensor, a Si micro-machined blazing grating, a customized 128-pixel LWIR mercury-cadmium-telluride (MCT) LN2 cooled detector array, proprietary signal processing technique, software and electronics. According to the current configuration, it was estimated that the total system weight to be ~4 kg, spectral resolution <4cm-1 and Noise Equivalent Spectral Radiance (NESR) <10-8 Wcm-2 sr-1cm-1 in 8 to 12 μm. System design and preliminary test results of some components will be presented. Upon the arrival of the MCT detector array, the prototype unit will be further tested and its performance validated in fall of 2007.
A promising way of improving the sensitivity of the LIBS (Laser-Induced Breakdown Spectroscopy) technique consists in using basically two successive laser pulses instead of only one as in conventional LIBS: the first pulse generates the plasma and the second pulse selectively excites a specific quantum level of a given trace atomic species inside the plasma. The effect of this second laser pulse is to increase the emission of the atomic species of interest and therefore enhance the signal-to-noise ratio, leading to an improved detection. As a first step toward the detection of Pb in various materials, we present in this work a study of the resonant excitation and decay paths of Pb atoms in a laser-produced plasma. The ablation was performed using a Nd:YAG laser and the 2nd pulse provided by an Optical Parametric Oscillator (OPO) laser was launched several μs afterwards.
In this study, we report for the first time the epitaxial growth of CBN thin films on Magnesium Oxide (MgO) substrates for optical device applications. A high deposition temperature (greater than or equal to to 800 oC) is required to obtain the epitaxial growth of CBN films. A parametric study is proposed in order to elaborate CBN thin films with a crystal structure as close as possible to that of a CBN bulk single crystal and with good optical characteristics. In particular, a low oxygen pressure (1 mTorr) allows synthesizing high-quality CBN thin films with an out-off plane lattice parameter comparable to the one of CBN bulk material at low surface roughness. The optical characterization of the high-quality CBN thin films reveals a high optical transmission (greater than or equal to 85 %) and a refractive index equal to 2.22 at 1.55 μm for certain deposition conditions. These optical properties clearly indicate the potential of CBN thin films for waveguide applications. This work presents a significant first step toward the integration and the potential use of CBN films for optical device applications.
The dynamics of ultrafast phase transition and reaction mechanisms can be deduced from ultrafast x-ray diffraction or absorption measurements. Femtosecond lasers have been used recently to study matter dynamics with optical-pump and x-ray probe spectroscopy, using monochromatic K alpha x-ray radiation. We present here our most recent progress in the development of a femtosecond time- resolved x-ray absorption spectroscopy (XAS) system based on a broadband soft x-ray source in the 1-5 nm range. The femtosecond XAS system is designed to probe the electronic dynamics occurring during the vanadium dioxide (VO2) semiconductor to metal phase transition following excitation by a femtosecond laser pulse. In the present experiments, broadband spectra near the vanadium L edge (511 eV) and oxygen K edge (525 eV) of VO2 have been generated and measured with simultaneously high signal to noise ratio (100), high spectral resolution (ΔE/E=4x10-3) and a 1.2 ps temporal resolution.
We have successfully fabricated two types of optical switch devices, namely, all-optical switch (VO2/quartz) and electro-optical switch (VO2/TiO2/ITO/glass) based on semiconductor-to-metallic phase transition characteristic of vanadium dioxide (VO2) smart coatings. The VO2 active layer, the TiO2 buffer layer, and the ITO transparent conductive electrode used in these devices, were achieved by reactive pulsed laser deposition. The optical switching of the fabricated devices was investigated at λ = 1.55 μm. The semiconductor (on) to metallic (off) phase transition was controlled by photoexcitation of VO2 in the case of the all-optical switch, and by an external electric-field between the ITO and the VO2 layer in the case of the electro-optical switch. The extinction ratio (on/off) is found to be much higher for the all-optical switch than for the electro-optical switch. For the all-optical switch, extinction ratio of about 22 dB and 12 dB are obtained in the transmission and reflection modes respectively. In the case of the electro-optical switch, the extinction ratio is about 12 dB in the transmission mode and 5 dB in the reflection mode.
In 1985, the discovery of chirped-pulse amplification (CPA) by G. Mourou and D. Strickland led to ultrashort and high energy pulse lasers. Since energy deposition of ultrashort pulses occurs with limited heat transfer and damages, potential applications of femtosecond lasers to corneal surgery are very promising. By focusing a femtosecond laser on a solid surface, matter is ablated and this process is strongly laser parameter dependent. The goal of the experiment presented here was to measure the femtosecond laser ablation thresholds for different corneal layers and hydrogels. Experiments have been realized with the INRS Ti:Sapphire laser (60fs-400ps, 800nm, 10Hz) and they constitute an initial step toward the development of a new type of high precision surgical tool for corneal microsurgery. Results will be compared to theoretical calculation for light-tissue interaction and propagation using the hydrodynamic code developed at INRS. Grant Identification: NSERC, FRSQ Research in Vision Network and China Scholarship 22836034.
Laser ablation deposition technique was used to deposit silicon carbide thin films on both Si(100) and quartz substrates. The deposition was accomplished by ablating SiC sintered ceramic targets, using a KrF (248 nm) excimer laser. At a laser intensity of about 1 X 109 W/cm2, substrate temperatures in the (25-700) degree(s)C range were investigated. When the deposition temperature is varied from 27 to 650 degree(s)C, (i) the density of a-SiC films increases from 2.6 to 3.0 g cm-3, while their mean roughness value (for a film thickness of about 1 micrometers ) slightly changes from 0.44 to 0.5 nm; (ii) the optical transmission of a-SiC films is significantly improved (the absorption coefficient at 632.8 nm wavelength was reduced by a factor of about 5); and (iii) their Si-C bond density, as determined by FTIR spectroscopy, increases from (13.1 +/- 1.3) to (23.4 +/- 2.4) 1022 bond cm-3. The increased number of Si-C bonds is correlated to the increase of the optical transmission. Over all the investigated deposition temperature range, the a-SiC films were found to be under high compressive stress around a mean value of about 1.26 GPa. The control of the stress of a-SiC films was achieved by means of post- thermal annealings and the annealed a-SiC films were successfully used to fabricate x-ray membranes.
We present a comparative study of the x-ray emission produced by laser plasma sources in short ((tau) L equals 0.6 ps) and long ((tau) L equals 0.6 ns) pulse regimes for copper and tantalum targets. The experiments at (tau) L equals 0.6 ps show that the x-ray conversion efficiency (eta) is still increasing with laser intensity between 2 X 1015 W/cm2 and 5 X 1016 W/cm2 for both sub-keV (0.1 - 0.75 keV) and keV (0.75 - 2 keV) ranges. In addition, we found that the optimum values (eta) at (tau) L equals 0.6 ps are at least 2 - 4 times lower than those at (tau) L equals 0.6 ns.
A review is given (intended for the non-expert) of the field of ultrashort laser pulses at ultra high intensities and their interactions with plasmas. The review covers progress and basic concepts for theory, modelling and experiments, with emphasis on the background aspects, the basic experimental considerations and some possible applications.
A laser-induced plasma is used for atomization, ionization, and excitation of elements in solid samples. The temporal and spatial behavior of the plasma is studied by observing the emission lines of neutral aluminum and magnesium. The optimal temporal choice was determined for our plasma spectrochemical analysis and a calibration curve for an aluminum-magnesium alloy was obtained.
We present recent results of our effort to develop an efficient, user-friendly, table-top ultrafast X-ray source. The factors affecting the duration and the intensity of the X-ray emission in the keV range are studied. Time-dependent calculation of the atomic physics coupled to a Fokker- Planck code is used for a quantitative analysis of the experimental results.
Slab germanium targets have been irradiated in a line focus geometry with 1-3 nsec FWHM, 1.06-micron laser pulses at irradiances of I equal to or less than 10 exp 13 W/sq cm. The effect of varying the rise-time of the driving laser pulse on the amplification of 3-3 soft X-ray lasing lines is investigated. Results of short-pulse (100 psec FWHM) experiments have also shown gain on the same lasing transitions, but at substantially higher irradiances of I equal to or greater than 3 x 10 exp 13 W/sq cm.
An overview of current activities in Canada is reported, including x-ray lithography studies based on laser plasma sources and x-ray mask development. In particular, the application of laser plasma sources for x-ray lithography is discussed, taking into account the industrial requirement and the present state of laser technology. The authors describe the development of silicon carbide membranes for x-ray lithography application. SiC films were prepared using either a 100 kHz plasma-enhanced chemical vapor deposition (PECVD) system or a laser ablation technique. These membranes have a relatively large diameter (> 1 in.) and a high optical transparency (> 50%). Experimental studies on stresses in tungsten films deposited with triode sputtering are reported.
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