In this paper we present a new method for shaping of a pulsed IR (λ=1550 nm) laser beam in silicon. The shaping is based on plasma dispersion effect (PDE). The shaping is done by a second pulsed pump laser beam at 532 nm which simultaneously and collinearly illuminates the silicon’s surface with the IR beam. Following the PDE, and in proportion to its spatial intensity distribution, the 532 nm laser beam shapes the point spread function (PSF) by controlling the lateral transmission of the IR probe beam. The use of this probe in laser scanning microscope allows imaging and wide range of contactless electrical measurements in silicon integrated circuits (IC) being under operation e.g. for failure analysis purposes. We propose this shaping method to overcome the diffraction resolution limit in silicon microscopy on and deep under the silicon surface depending on the wavelength of the pump laser and its temporal pulse width. This approach is similar to the stimulated emission depletion (STED) concept previously introduced in scanning fluorescence microscopy.
A critical limitation imposed on all imaging systems is to achieve an optimal balance between optical resolution and bandwidth. The optical system determines and affects the relations between temporal information, spatial bandwidth, and resolution, so the resulting signal may differ for each wavelength. This is of significant importance for hyperspectral imaging in particular, because it extracts both spatial and temporal wavelength information. We present a dispersive device that can be used for hyperspectral imaging hypercube image measurements. We utilize the Vernier effect by integrating two silicon slabs that act together as a modified Fabry–Perot filter. The transition between wavelength bands is achieved by heating, utilizing the thermo-optic effect. Importantly, we show that red-shifting with concatenated slabs requires less heating than with a single slab. With the presented technique, a wide effective free spectral range of up to 90 nm around a central wavelength of 1550 nm was achieved along with 20-nm full-width-at-half-maximum resolution. With the same configuration, observing a narrower 0.7-nm free spectral range bandwidth, a fine spectrum resolution of 0.07 nm was obtained. Such variety covers most of the spatial and temporal standard limitations of current hyperspectral imaging requirements.
In this presentation we demonstrate how light can be useful both for sensing as well as for treating different types of inflammations and infections. In respect to sensing we show how a laser and a camera based system can be used in order to “hear” from a distance the “sounds” of e.g. the lungs while realizing a non-contact stethoscope which can be useful for detection of inflammable lungs diseases such as asthma. In respect to treating inflammations and infections with light, we will show how special light sources can be used in order to destroy candida nail infection or how combination of laser light together with gentamicin antibiotic can significantly enhancement the susceptibility of a bacteria such as P. aeruginosa.
Optical filters are required to have narrow band-pass filtering in the spectral C-band for applications such as signal tracking, sub-band filtering or noise suppression. These requirements lead to a variety of filters such as Mach-Zehnder interferometer inter-leaver in silica, which offer thermo-optic effect for optical switching, however, without proper thermal and optical efficiency. In this paper we propose tunable thermo-optic filtering device based on coated silicon slab resonator with increased Q-factor for the C-band optical switching. The device can be designed either for long range wavelength tuning of for short range with increased wavelength resolution. Theoretical examination of the thermal parameters affecting the filtering process is shown together with experimental results. Proper channel isolation with an extinction ratio of 20dBs is achieved with spectral bandpass width of 0.07nm.
In attempt to supply a reasonable fire plume detection, multinational cooperation with significant
capital is invested in the development of two major Infra-Red (IR) based fire detection alternatives,
single-color IR (SCIR) and dual-color IR (DCIR). False alarm rate was expected to be high not only as a
result of real heat sources but mainly due to the IR natural clutter especially solar reflections clutter.
SCIR uses state-of-the-art technology and sophisticated algorithms to filter out threats from clutter.
On the other hand, DCIR are aiming at using additional spectral band measurements (acting as a
guard), to allow the implementation of a simpler and more robust approach for performing the same
In this paper we present the basics of SCIR & DCIR architecture and the main differences between
them. In addition, we will present the results from a thorough study conducted for the purpose of
learning about the added value of the additional data available from the second spectral band. Here
we consider the two CO<sub>2</sub> bands of 4-5 micron and of 2.5-3 micron band as well as off peak band
(guard). The findings of this study refer also to Missile warning systems (MWS) efficacy, in terms of
operational value. We also present a new approach for tunable filter to such sensor.
Utilizing the surface plasmon resonance (SPR) effect of gold nanoparticles (GNPs) enables their using as contrast agents in a variety of biomedical applications for diagnostics and treatment. These applications use both the very strong scattering and absorption properties of the GNPs due to their SPR effects. Most imaging methods use the light-scattering properties of the GNPs. However, the illumination source is in the same wavelength of the GNPs scattering wavelength, leading to background noise caused by light scattering from the tissue. In this paper we present a method to improve border detection of regions enriched with GNPs aiming for real time application of complete tumor resection by utilizing the absorption of specially targeted GNPs using photothermal imaging. Phantoms containing different concentrations of GNPs were irradiated with continuous-wave laser and measured with a thermal imaging camera which detected the temperature field of the irradiated phantoms. By modulating the laser illumination, and use of a simple post processing, the border location was identified in accuracy of better than 0.5 mm even when the surrounding area get heated. This work is in continuation to our previous research<sup> 1</sup>.
In this paper we present gold nanoparticles coated with silicon that switch the order between the scattering and the absorption magnitude at the resonance peak and tune the plasmon resonance over the spectrum. This is obtained by modifying the refractive index of the silicon coating of the nanoparticle by illuminating it with a pumping light due to the plasma dispersion effect in silicon. We also report how changing the diffraction limited point spread function through the utilization of plasma dispersion effect of the above mentioned silicon coated nanoparticles allows doing imaging with sub wavelength resolution. The plasma dispersion effect can increase the absorption coefficient of the silicon, when illuminated with a focused laser beam and as explained above it can also tune the absorption versus scattering properties of the nanoparticle. Due to the Gaussian nature of the laser illumination which has higher intensity at its peak, the plasma dispersion effect is more significant at the center of the illumination. As a consequence, the reflected light from probe beam at the near infra-red region has a sub wavelength dip that overlaps with the location of the pump illumination peak. This dip has a higher spatial frequency than an ordinary Gaussian, which enables to achieve super resolution.
In this paper we present an all-optical silicon modulator, where a silicon slab (450 μm) thick is coated on both sides to get a Fabry-Perot resonator for laser beam at wavelength of 1550nm. Most of the modulators discussed in literature, are driven by electrical field rather than by light. We investigate new approaches regarding the dependence of the absorption of the optical signal on the control laser pulse at 532 nm having 5nm pulse width. Our silicon based Fabry-Perot resonator increases the intrinsic c-Si finesse to >10, instead of the uncoated silicon with natural finesse of 2.5. The improved finesse is shown to have significant effect on the modulation depth using a pulsed laser. A modulation of 12dB was attained. The modulation is ascribed to two different effects - The Plasma Dispersion Effect (PDE) and the Thermo- Optic Effect (TOE). The PDE causes increase in the signal absorption in silicon via the absorption of the control laser light. On top of that, the transmission of the signal can decrease dramatically in high finesse resonators due to change in the refractive index due to TOE. The changes in the signal's absorption coefficient and in the refractive index are the result of incremental change in the concentration of free carriers. The TOE gives rise to higher refractive index as opposed to the PDE which triggers a decrease in the refractive index. Finally, tradeoff considerations are presented on how to modify one effect to counter the other one, leading to an optimal device having reduced temperature dependence.