This PDF file contains the front matter associated with SPIE Proceedings Volume 9956, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

We have constructed an electron gun that delivers highly charged femtosecond electron pulses to a target with kHz repetition rate. Electron pulses are generated by femtosecond laser pulses in a photoemission process and are accelerated up to 100 kV and compressed to sub-picosecond duration. Compression is essential to compensate for the space charge effect that increases the size of electron pulses in all directions significantly. The pulses are compressed transversely by magnetic lenses and longitudinally by the longitudinal electric field of a radio-frequency cavity. The longitudinal compression is achieved by decelerating the electrons in the leading edge of the pulse, and accelerating the electrons in the trailing edge of the pulse. This results in the pulse compressing and reaching the minimum pulse duration at a known distance from the compression cavity. The short pulse duration and high repetition rate will be essential to observe subpicosecond dynamic processes in molecules in gas phase with a good signal to noise ratio. A streak camera, consisting of a millimeter-sized parallel plate capacitor, was used to measure the pulse duration in situ.

Ultrafast electron diffraction (UED) is a powerful technique that can be used to resolve structural changes of gas molecules during a photochemical reaction. However, the temporal resolution in pump-probe experiments has been limited to the few-ps level by the space-charge effect that broadens the electron pulse duration and by velocity mismatch between the pump laser pulses and the probe electron pulses, making only long-lived intermediate states accessible. Taking advantage of relativistic effects, Mega-electron-volt (MeV) electrons can be used to suppress both the space-charge effect and the velocity mismatch, and hence to achieve a temporal resolution that is fast enough to follow coherent nuclear motion in the target molecules. In this presentation, we show the first MeV UED experiments on gas phase targets. These experiments not only demonstrate that femtosecond temporal resolution is achieved, but also show that the spatial resolution is not compromised. This unprecedented combination of spatiotemporal resolution is sufficient to image coherent nuclear motions, and opens the door to a new class of experiments where the structural changes can be followed simultaneously in both space and time.

Recent experiments have shown that by combining a femtosecond laser with an electron microscope, dynamics at the nanoscale with femtosecond temporal resolution can be followed. These ultrafast electron microscopy (UEM) techniques have allowed a variety of experimental studies on nanoscale material systems to be conducted, including the ability to image plasmon dynamics in real time. We will discuss how UEM can also be used to study fundamental quantum problems, present some recent experimental results and we will discuss how future experimental improvements will push the temporal resolution from hundreds of femtoseconds down to the single femtosecond regime and below.

Molecular structure determination of chemical reactions or processes has been one of the grand challenges in physics, chemistry, and biology. To image these processes, it typically requires sub-Angstrom spatial and femtosecond temporal resolutions. One of the standard imaging techniques, X-ray diffraction, however, currently suffers from temporal jitters and is available only at large facilities. Furthermore, it also suffers from very low elastic scattering cross sections, which make it difficult to apply to gas phase molecules. Another technique, ultrafast electron diffraction (UED), overcomes this low cross section problem, but the temporal resolution is still limited to hundreds of femtoseconds, mainly due to Coulomb repulsion in electron beam and velocity mismatch between laser-pump pulse and electron probe pulse in a typical pump-probe scheme. The recently proposed laser-induced electron diffraction (LIED) is based on two basic ideas. First, an electron wave packet can be generated from a target itself by an intense laser pulse and driven back within the subsequent half-cycle of the laser to rescatter from the parent ion, thus realizing a self-imaging process. Laser-free elastic differential cross sections (DCS) can then be extracted from high-energy electron spectra, as demonstrated by the Quantitative Rescattering theory (QRS). Second, the target structure information can be retrieved from the DCS. This retrieval is further simplified by using back-scattered electrons with collision energy of about 100 eV, for which the independent-atom model (IAM) can be employed to quite accurately simulate the DCS. Demonstration of ultrafast imaging with the LIED has been reported so far on simple diatomic molecules. Here we discuss recent progress in LIED with polyatomic molecules in two examples. The first one is aligned acetylene (C2H2) and the second one is benzene (C6H6). In both cases, two bond lengths, C-C and C-H have been successfully retrieved. For even more complex polyatomic molecules with many bond lengths and bond angles, the method using simple fitting to DCS would not work, while the 1D Fourier transform method cannot resolve bonds of similar lengths. We show that these difficulties can be overcome by using the 2D Fourier transform method which allows retrieving 2D information from laser aligned polyatomic molecules.

Compared with other imaging probes such as fluorescent dyes and quantum dots, second-harmonic radiating imaging probes (SHRIMPs) provide a unique ultrafast, coherent optical contrast that is free of photobleaching and emission intermittency. Using the second-harmonic signal emitted from SHRIMPs, harmonic holography achieves threedimensional holographic imaging with a color contrast similar to fluorescence microscopy where the uninterested background scattering is efficiently suppressed by an optical filter. The coherent contrast provided by SHRIMPs also enables imaging through turbid media via digital phase conjugation. Here we review the developments and applications of SHRIMPs and harmonic holography.

Layered two-dimensional (2D) materials possess unique optical properties. For example, the monolayer family of Transition Metal Dichalcogenide (TMD) materials (such as WS2 and MoS2) is well known for the existence of a direct band gap. In this talk, we discuss the characterization of the second order nonlinear susceptibility in mono- or few-layer TMDs, which have been recently shown to exhibit extraordinary second harmonic generation. We investigate the large nonlinear response due to resonance enhancement. Theoretical analysis will be discussed and compared with experimental results.

Surface enhanced Raman scattering (SERS) is a popular technique for detecting and analyzing molecules at very low concentrations. The sensitivity of SERS is high enough to detect single molecules. It has proven difficult, however, to perform similar measurements in the so-called nonlinear optical regime, a regime in which the molecule is responding to multiple light pulses. Nonetheless, recent experiments indicate that after careful optimization, it is possible to generate signals derived from nonlinear analogs of SERS. Such measurements make it possible to view molecular vibrations in real time, which amounts to the femto- to pico-second range. In this contribution, we discuss in detail under which conditions detectable surface-enhanced coherent Raman signals can be expected, provide experimental evidence of coherent Raman scattering of single molecules, and highlight the unique information that can be attained from such measurements.

Low-wavenumber Raman spectroscopy has long been demonstrated as a method of optical characterization in a variety of applications, such as thermal detection and semiconductor analysis. However, accessing low-wavenumber Raman shifts remains a challenge, usually requiring an expensive and complex multi-stage spectrographic system to measure several cm-1 Raman shifts. In this work, we demonstrate a method to measure low-wavenumber Raman shifts down to 1 cm-1 using atomic filters. By using a narrow-band Faraday anomalous dispersion optical filter to remove spontaneous emission noise from the laser cavity and a heated atomic cell as a notch filter to remove the excitation laser, the system is able to measure low Raman shifts (down to 1 cm-1). To demonstrate the capabilities, we measure the broadband Raman spectrum from a silica optical fiber with approximately 0.3 cm-1 resolution, detecting both Stokes and Anti-Stokes Raman shift as low as 0.7 cm-1.

Ultrahigh-quality whispering gallery mode optical microresonators have been studied for their use as highly sensitive sensors. In this talk, we discuss the use of microsphere microresonators in Raman spectroscopy for interrogating particles adhered to the surface of the resonator. An external cavity diode laser is tuned to a resonant high-Q mode and the circulating optical field experiences a large buildup, resulting in enhanced Raman scattering. Here we present studies of Raman scattering spectroscopy of single particles. Raman sensing with different Q's is discussed.

When a UV photon is absorbed by a single semiconductor nanocrystal (NC), two or more excitons can be simultaneously generated through the carrier multiplication (CM) process. It is still highly debated whether the CM efficiency is truly enhanced in semiconductor NCs because all the routine CM measurements performed exclusively at the ensemble level are incapable of completely excluding the false CM signals contributed by the charged excitons. Here we place single CdSe NCs above an aluminum film and successfully resolve their UV-excited photoluminescence time trajectories where the true and false CM signals are contained in the blinking “on” and “off” levels, respectively. When the UV photon energy is ~2.46 times of the NC energy gap, an average CM efficiency of ~20.2% can be reliably estimated. The ability to detect UV-excited photoluminescence from a single NC will surely provide a great guidance for the CM applications in various light-to-electric conversion devices.

Infrared excited and visible emitting upconverting nanoparticles show potential applications in the fields of photovoltaics, and in single molecule bio-imaging. We show enhanced upconversion luminescence, of up to 50-fold, at the single particle level, via subwavelength interference of the infrared excitation and visible emission. Single particle upconverted spectra and time-resolved decay, correlated with AFM, show enhanced emission at 545nm and 650 nm, whereby the magnitude of the enhancement is dependent on the thickness of the interference layer, and on the excitation intensity. We correlate our experimental results with finite element modeling showing both enhanced excitation and emission as a function of the interference layer thickness.

The plasmonic metamaterial perfect absorber (MPA) is a recently developed branch of metamaterial which exhibits nearly unity absorption within certain frequency range.[1-6] The optically thin MPA possesses characteristic features of angular-independence, high Q-factor and strong field localization that have inspired a wide range of applications including electromagnetic wave absorption,[3, 7, 8] spatial[6] and spectral[5] modulation of light,[9] selective thermal emission,[9] thermal detecting[10] and refractive index sensing for gas[11] and liquid[12, 13] targets. In this work, we demonstrate a MPA working at terahertz (THz) regime and characterize it using an ultrafast THz time-domain spectroscopy (THz-TDS). Our study reveal an ultra-thin Fabry-Perot cavity mechanism compared to the impedance matching mechanism widely adopted in previous study [1-6]. Our results also shows higher-order resonances when the cavities length increases. These higher order modes exhibits much larger Q-factor that can benefit potential sensing and imaging applications. [1] C. M. Watts, X. L. Liu, and W. J. Padilla, "Metamaterial Electromagnetic Wave Absorbers," Advanced Materials, vol. 24, pp. 98-120, Jun 19 2012. [2] M. Hedayati, F. Faupel, and M. Elbahri, "Review of Plasmonic Nanocomposite Metamaterial Absorber," Materials, vol. 7, pp. 1221-1248, 2014. [3] N. I. Landy, S. Sajuyigbe, J. J. Mock, D. R. Smith, and W. J. Padilla, "Perfect metamaterial absorber," Physical Review Letters, vol. 100, p. 207402, May 23 2008. [4] H. R. Seren, G. R. Keiser, L. Cao, J. Zhang, A. C. Strikwerda, K. Fan, et al., "Optically Modulated Multiband Terahertz Perfect Absorber," Advanced Optical Materials, vol. 2, pp. 1221-1226, 2014. [5] D. Shrekenhamer, J. Montoya, S. Krishna, and W. J. Padilla, "Four-Color Metamaterial Absorber THz Spatial Light Modulator," Advanced Optical Materials, vol. 1, pp. 905-909, 2013. [6] S. Savo, D. Shrekenhamer, and W. J. Padilla, "Liquid Crystal Metamaterial Absorber Spatial Light Modulator for THz Applications," Advanced Optical Materials, vol. 2, pp. 275-279, 2014. [7] H. Tao, N. I. Landy, C. M. Bingham, X. Zhang, R. D. Averitt, and W. J. Padilla, "A metamaterial absorber for the terahertz regime: Design, fabrication and characterization," Optics Express, vol. 16, pp. 7181-7188, May 12 2008. [8] J. Hao, J. Wang, X. Liu, W. J. Padilla, L. Zhou, and M. Qiu, "High performance optical absorber based on a plasmonic metamaterial," Applied Physics Letters, vol. 96, p. 251104, 2010. [9] X. Liu, T. Tyler, T. Starr, A. F. Starr, N. M. Jokerst, and W. J. Padilla, "Taming the Blackbody with Infrared Metamaterials as Selective Thermal Emitters," Physical Review Letters, vol. 107, p. 045901, 07/18/ 2011. [10] T. Maier and H. Brückl, "Wavelength-tunable microbolometers with metamaterial absorbers," Optics Letters, vol. 34, pp. 3012-3014, 2009/10/01 2009. [11] A. Tittl, P. Mai, R. Taubert, D. Dregely, N. Liu, and H. Giessen, "Palladium-Based Plasmonic Perfect Absorber in the Visible Wavelength Range and Its Application to Hydrogen Sensing," Nano Letters, vol. 11, pp. 4366-4369, 2011/10/12 2011. [12] N. Liu, M. Mesch, T. Weiss, M. Hentschel, and H. Giessen, "Infrared Perfect Absorber and Its Application As Plasmonic Sensor," Nano Letters, vol. 10, pp. 2342-2348, Jul 2010. [13] G. H. Li, X. S. Chen, O. P. Li, C. X. Shao, Y. Jiang, L. J. Huang, et al., "A novel plasmonic resonance sensor based on an infrared perfect absorber," Journal of Physics D-Applied Physics, vol. 45, p. 205102, May 23 2012.

ZnO nanorod/wire is a nanomaterial that possessing high surface area to volume ratio and excellent optical and electrical properties, indicating its promising sensing capabilities in various applications. Here, we present the research work of ZnO nanorod/wire based sensors carried out in our lab, which were used in the optical, electrical and mechanical sensing areas, respectively. In optical sensing, a ZnO nanorod array was fabricated at the endface of an optical fiber, forming a sensing probe, whose interference spectrum shifts upon the exposure to gas analyte. In electrical sensing, the ZnO nanowires decorated extended-gate field-effect transistor was used as a pH sensor, whose source-drain current changed dramatically under different pH values when applying the same gate voltage. Finally, regarding to the mechanical sensing, the ZnO nanorods were applied to the surface of the solidly mounted resonator for gas detecting, whose resonant frequency shifts due to the absorption of gas analytes.

Beta-site APP cleaving enzyme 1 (BACE1) is a type I transmembrane aspartyl protease. In the amyloidogenic pathway, BACE1 provides β-secretase activity that cleaves the amyloid precursor protein (APP) that leads to amyloid beta (Aβ) peptides. The aggregation of these Aβ will ultimately results in amyloid plaque formation, a hallmark of Alzheimer’s disease (AD). Amyloid aggregation leads to progressive memory impairment and neural loss. Recent detergent protein extraction studies suggest that the untreated BACE1 protein forms a dimer that has significantly higher catalytic activity than its monomeric counterpart. Here, we examine the dimerization hypothesis of BACE1 in cultured HEK293 cells using fluorescence correlation spectroscopy (FCS). Cells were transfected with a BACE1-EGFP fusion protein construct and imaged using confocal and DIC microscopy to monitor labeled BACE1 localization and distribution within the cell. Our one-photon fluorescence fluctuation autocorrelation of BACE1- EGFP on the plasma membrane of HEK cells is modeled using two diffusing species on the plasma membrane with estimated diffusion coefficients of 1.39 x 10^-7 cm²/sec and 2.8 x 10^-8 cm²/sec under resting conditions and STA-200 inhibition, respectively. Anomalous diffusion model also provided adequate description of the observed autocorrelation function of BACE1- EGFP on the plasma membrane with an estimate exponent (α) of 0.8 and 0.5 for resting and STA-200 treated cells, respectively. The corresponding hydrodynamic radius of this transmembrane fusion protein was estimated using the measured diffusion coefficients assuming both Stokes-Einstein and Saffman-Delbruck models. Our results suggest a complex diffusion pattern of BACE1-EGFP on the plasma membrane of HEK cells with the possibility for dimer formation, especially under STA-200 inhibition.

We will present some crucial design consideration for optical imaging/interferometry based biosensors.

Fiber-optic based diffuse reflectance spectroscopy (DRS) is shown to be a highly specific and highly sensitive method for non-invasive detection of various cancers (e.g. cervical and oral) as well as many other diseases. Fiber-optic DRS diagnosis relies on non-invasive biomarker detection (e.g. oxy- and deoxy-hemoglobin) and can be done without the need for sophisticated laboratory analysis of samples. Thus, it is highly amenable for clinical adoption especially in resource scarce regions that have limited access to such developed laboratory infrastructure. Despite the demonstrated effectiveness of fiber-optic DRS, such systems remain cost prohibitive in many of these regions, mainly due to the use of bulky and expensive spectrometers. Here, a fiber-optic DRS system is coupled to a smartphone spectrometer and is proposed as a low-cost solution for non-invasive tissue hemoglobin sensing. The performance of the system is assessed by measuring tissue phantoms with varying hemoglobin concentrations. A DRS retrieval algorithm is used to extract hemoglobin parameters from the measurements and determine the accuracy of the system. The results are then compared with those of a previously reported fiber-optic DRS system which is based on a larger more expensive spectrometer system. The preliminary results are encouraging and indicate the potential of the smartphone spectrometer as a viable low-cost option for non-invasive tissue hemoglobin sensing.

Biocompatible and even biodegradable polymers have unique advantages in various biomedical applications. Recent years, photonic devices fabricated using biocompatible polymers have been widely studied. In this work, we manufactured an optical fiber using biodegradable polymer POC and POMC. This step index optical fiber is flexible and easy to handle. Light was coupled into this polymer fiber by directly using objective. The fiber has a good light guiding property and an approximate loss of 2db/cm. Due to the two layer structure, our fiber is able to support applications inside biological tissue. Apart from remarkable optical performance, our fiber was also found capable of performing imaging. By measuring the impulse response of this multimode polymer fiber and using the linear inversion algorithm, concept proving experiments were completed. Images input into our fiber were able to be retrieved from the intensity distribution of the light at the output end. Experiment result proves the capability of our optical fiber to be used as a fiber endoscopy no needs to remove.

Semiconductors systems exhibiting excitonic properties are discussed in terms of their coherent response, which is extracted using two-dimensional coherent spectroscopy. This control method allows for separation of quantum pathways that comprise the optical response, such as interactions between excitons, their dephasing rates, the effects of many-body interactions and the role of structure on the microscopic electronic environment. Additional controls, such as polarization can be used to further distinguish biexcitons and suppress many-body interactions. These result are compared and contrasted with those from a semiconductor microcavity where the excitons form polaritonic modes due to normal-mode splitting. Rephrasing spectra map the detuning dependence of the exciton-polariton branches. Increasing the detuning shifts all features to higher energy and the expected anti-crossing is observed. An isolated biexciton is seen only at negative detuning, separated by a binding energy. For positive detuning, the spectral weight of the off-diagonal features swap, as the lower polariton branch and biexciton come into resonance. This indicates that the off-diagonal features are sensitive to the interactions of the exciton-polaritons and other resonances in the system.

We capture the spatio-temporal oscillations within large individual ferroelectric domains and across domain walls upon optical excitation in a single crystal of BaTiO3 with ~350 nm lateral resolution and ~100 ps temporal resolution using synchrotron x-ray pulses as probes. Spatially resolved ultrafast mapping across domain walls reveals that the optical excitation pump can generate GHz acoustic standing waves of different frequencies between the surface and buried domain wall interfaces at different depths. Phase-field simulations reveal that a thermo-electro-acoustic mechanism can quantitatively explain the observed dynamics. The study reveals the importance of combined spatial and temporal resolution for understanding ultrafast dynamics in inhomogeneous microstructures.

We investigate the possibility for superluminality effects at the femtosecond pulse propagation in the medium with nanorods, if second harmonic generation (SGH) and two-photon luminescence (TPL) take place. On basis of semiclassical approach, we derive a set of equations, which describe the atomic states and electric fields dynamics. We show the possibility of light acceleration and soliton formation, if nanorod aspect ratio changing occurs due to their reshaping because two photon absorption (TPA) of optical energy, and investigate TPL and SHG in the medium with nanorods under sequential one-photon absorptions.

The ultrafast temporal dynamics of a single ZnO nanowire is probed using an ultraviolet femtosecond Kerr-gated wide field fluorescence microscope. The microscope is a comprehensive tool that not only operates in steady state and transient mode but can also function as both an ultrafast imaging instrument as well as a femtosecond fluorescence spectrometer. The sub 90 femtosecond temporal resolution and sub micron spatial resolution facilitate the measurement of ultrafast dynamics of single nanostructures. The steady state and temporal emission from a single ZnO nanowire is observed at different fluences. At high fluences the carrier density exceeds that of the Mott density and bandgap renormalization is observed in the transient spectra. Morphological anomalies resulted in enhanced localized emission from regions along the nanowire. Selective area analysis facilitated extraction of emission dynamics from a single region on the nanowire and provided insight into how structural inhomogeneities affect ultrafast phenomenon occurring in a single nanowire.

We have developed a new method, transient grating photoluminescence spectroscopy (TGPLS), allowing the collection of broadband ultrafast photoluminescence spectroscopy with low photoluminescence background. In TGPLS, two ultrafast laser pulses generate a multiplexed transient grating (TG) by the optical Kerr effect. The gated signal is diffracted by the TG and spatially separated from background fluorescence. This high performance nonlinear optical gate delivers time resolution less than 200 fs, spectral bandwidth covering the entire visible region with extremely low fluorescence background. Here we present two applications of TGPLS that provide deeper insight into ultrafast energy transfer in multi-chromophore perylene arrays and ultrafast structural relaxation in oligothiophenes.

Complex oxides and strongly correlated electron systems are at the forefront of science due to their exquisite potential for optical, spintronic, transducing/actuating, multiferroic, electrochemical, and superconducting property enhancements. Accordingly, at the nanoscale, engineering of complex oxide compounds is a promising route for discovery of novel quantum functionalities in a vast space of synthesis technique, calling for high-resolution control and visualization of physical properties and their structural basis. The advent of optical pulse techniques and related instrumentation advances is used to access dynamical separation of correlated orders that hide at equilibrium and also to create novel phases, not available via mainstream synthesis techniques. In this this talk, I will discuss resonant and non-resonant spectroscopic manipulation of phase transitions in nanoferroic oxides, focusing on ultrafast optical creation of artificial supercrystals in epitaxial superlattices. While table top nonlinear optical techniques are used to access the ferroic properties, synchrotron based time-resolved structural techniques, including diffraction and spectroscopy are decisive tools for revealing the nature of orderings in superstructures, their symmetries, phase quantification and spatial distribution with sub-micron resolution.

Mid-infrared photothermal spectroscopy is a pump-probe technique for label-free and non-destructive sample characterization by targeting intrinsic vibrational modes. In this method, the mid-infrared pump beam excites a temperature-induced change in the refractive index of the sample. This laser-induced change in the refractive index is measured by a near-infrared probe laser using lock-in detection. At increased pump powers, emerging nonlinear phenomena not previously demonstrated in other mid-infrared techniques are observed. Nonlinear study of a 6 μm-thick 4-Octyl-4’-Cyanobiphenyl (8CB) liquid crystal sample is conducted by targeting the C=C stretching band at 1606 cm^-1. At high pump powers, nonlinear signal enhancement and multiple pitchfork bifurcations of the spectral features are observed. An explanation of the nonlinear peak splitting is provided by the formation of bubbles in the sample at high pump powers. The discontinuous refractive index across the bubble interface results in a decrease in the forward scatter of the probe beam. This effect can be recorded as a bifurcation of the absorption peak in the photothermal spectrum. These nonlinear effects are not present in direct measurements of the mid-infrared beam. Evolution of the nonlinear photothermal spectrum of 8CB liquid crystal with increasing pump power shows enhancement of the absorption peak at 1606 cm^-1. Multiple pitchfork bifurcations and spectral narrowing of the photothermal spectrum are demonstrated. This novel nonlinear regime presents potential for improved spectral resolution as well as a new regime for sample characterization in mid-infrared photothermal spectroscopy.

Precise synchronization between radio frequency and mode-locked laser pulses provides a high resolution capability for detecting either time jitter in laser pulse train or phase noise in radio frequency. In this talk, we will present our recent progresses on radio frequency dissemination and fiber optical sensing based on sub-femtosecond level synchronization between radio frequency and mode-locked pulse train.

This talk will describe new computational microscopy methods for high pixel-count 3D images. We describe two setups employing illumination-side and detection-side aperture coding of angle (Fourier) space for capturing 4D phase-space (e.g. light field) datasets with fast acquisition times. Using a multi-slice forward model and compressive sensing inspired algorithms, we develop efficient 3D reconstruction methods for both incoherent and coherent imaging models, with robustness to scattering and aberrations. Experimentally, we achieve real-time 3D intensity and phase capture with high resolution across a large volume. Such computational approaches to optical microscopy add significant new capabilities to commercial microscopes without significant hardware modification. We will discuss applications in 3D microscopy and all-optical neural activity tracking.

With the development of mode-division-multiplexing (MDM), few mode fibers (FMFs) have found a wide range of applications in optical sensing and communications. However, how to precisely control the mode composition of optical signals in FMFs remains a difficult challenge. In this paper, we present an adaptive mode control method that can selectively excite the linearly polarized (LP) mode within the FMF. The method is based on using optical pulses reflected by a fiber Bragg grating (FBG) for wavefront optimization. Two potential applications are discussed. First, we theoretically demonstrate the feasibility of large scale multiplexing of absorption based fiber optical sensors. Second, we discuss the possibility of using mode dependent loss to reconstruct the spatial distributions of absorptive chemicals diffused within a FMF.

One of the surprises of nonlinear optics, is that light may interact strongly with sound. Intense laser light literally “shakes” the glass in optical fibres, exciting acoustic waves (sound) in the fibre. Under the right conditions, it leads to a positive feedback loop between light and sound termed “Stimulated Brillouin Scattering,” or simply SBS. This nonlinear interaction can amplify or filter light waves with extreme precision in frequency which makes it uniquely suited to solve key problems in the fields of defence, biomedicine, wireless communications, spectroscopy and imaging. We have achieved the first demonstration of SBS in compact chip-scale structures, carefully designed so that the optical fields and the acoustic fields are simultaneously confined and guided. This new platform has opened a range of new functionalities that are being applied in communications and defence with breathtaking performance and compactness. My talk will introduce this new field and review our progress and achievements, including silicon based optical phononic processor.

Non-degenerate 2-photon excitation of a fluorophore with two laser beams of different photon energies may offer independent degree of freedom in tuning of the photon flux (i.e., the power) for each beam. Wereport a practical demonstration that the emission intensity of a fluorophore excited in the non-degenerate regime in scattering medium is more efficient than the commonly used degenerate 2-photon excitation. In our experiments we use spatially and temporally aligned Ti:Sapphiremode-locked laser and optical parametric oscillator beams operating at near infrared (NIR) and short-wavelength infrared (SWIR) optical frequencies, respectively. The non-degenerate 2-photon excitation mechanism takes advantage of the infrared wavelengths used in 3-photon microscopy to achieve increased penetration depth, while preserving relatively high 2-photon excitation cross section, exceeding that achievable with the 3-photon excitation. Importantly, independent control of power for each beam implies that the flux requirement for the higher photon energy NIR beam, which experiences higher scattering in biological tissue, can be relaxed at the expense of increasing the flux of the lower photon energy SWIR beam which experiences lower scattering, thus promising deeper penetration with higher efficiency of excitation.Applications for in vivo brain imaging will be also discussed.

The work presents the results of studies of samples of human articular surface of the knee joint, obtained by Raman spectroscopy implementedduring endoprosthesis replacement surgery . The main spectral characteristics of articular surface areas with varying degrees of cartilage damage were detected at 956 cm^-1, 1066 cm^-1 wavenumbers, corresponding to phosphate and carbonate, and at 1660 cm^-1, 1271 cm^-1 wavenumbers, corresponding to amide I and amide III. Criteria allowing to identify the degree of articular hyaline cartilage damage were introduced.

This work presents the results of spectral analysis of biopolymer materials that are implemented in medical sphere. Polymer samples containing polycaprolactone and iron oxides of different valence were used in the studies. Raman spectroscopy method was used as a main control method. Relative content of iron and polycaprolactone in studied materials was assessed using ratio of RS intensities values at 604 cm^-1 and 1726 cm^-1 wavenumbers to intensity value of 1440 cm^-1 line.