This PDF file contains the front matter associated with SPIE Proceedings Volume 10753, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Attosecond pulses are generated by electrons that are extracted from a quantum system by an intense light pulse and travel through the continuum under the influence of the electric field of the light. Portions of each electron wave packet are forced to re-collide with its parent ion after the field reverses direction. Upon re-collision, the electron and ion can recombine, emitting soft x-ray radiation that can be in the form of attosecond pulses. This highly nonlinear process occurs in atoms, molecules and solids and offers unique measurement opportunities – for measuring the attosecond pulse itself; the orbital(s) from which it emerged; and the band structure of material in which the wave packets moved.

Coherent Raman scattering (CRS) is a popular technique for ultrafast spectroscopy and microscopy studies. CRS is based on a third-order nonlinear light-matter interaction, characterized by a nonlinear susceptibility with nonzero elements for bulk samples. It is challenging to perform CRS measurements at interfaces, as bulk contributions can often overwhelm. We have developed a surface-sensitive approach for CRS spectroscopy and microscopy, which enhances the sensitivity to interfacial processes by at least tenfold.

Utilization of transient reflectivity measurements for nondestructive characterization of material properties are attractive for understanding materials behavior in harsh environments. Two experimental approaches that implement an all optical pump-probe ultrafast spectroscopy will be presented. In picosecond ultrasonics, the pump beam is used to generate ultrasonic wave modes propagating normal to the surface. Transient reflectivity signal exhibits Brillouin oscillations that originate from the interference between two reflections of the probe beam: one from the surface and another from the wavefront of the acoustic wave. The frequency and amplitude of the oscillations depends on the type and velocity of the excited modes and is determined by the crystalline orientation. These features are used to obtain microstructural information of the material. Application of the method to subsurface grain boundary imaging in transparent metal oxides will be presented. The transient thermoreflectance method is used to characterize conductive heat transfer in solid materials, particularly, across interface and grain boundaries. In this approach, the pump beam is used as a heater, and the probe beam measures temperature induced reflectivity changes. Measured reflectivity profiles in the time and spatial domain are analyzed to characterize the heat transfer characteristics of the material with a few micrometer spatial resolution. Examples include measurement of radiation damage induced thermal conductivity degradation in ceramic materials such silicon carbide and cerium dioxide and thermal transport across the interfaces in ceramic matrix composite materials. Presented methods combined with other methods such as Raman spectroscopy offer capability to characterize material properties nondestructively and are attractive methods for in-situ studies of materials behavior in harsh environments.

Recently there have been strong interest in understanding and manipulating the effects of local grain boundary microstructures on the charge transfer and photovoltaics performance of newly discovered organometal halide perovskite materials. The development of ultrafast broadband spectroscopic nano-imaging methods from visible to terahertz reveals a wide range of unexpected details in these materials. In this talk, I will discuss our results obtained from ultrafast microscopy and particularly, provide insights on some of the most puzzling questions: are local grain microstructures cooperative or destructive on charge transfer and collection? How to understand non-equilibrium photocarrier transport and differentiate carrier depletion pathways at single grain/gain boundary level? Finally I will also discuss our development of ultrafast THz imaging tools to facilitate understanding of these issues.

Using time- and spatially-resolved hard X-ray diffraction microscopy, the striking structural and electrical dynamics upon optical excitation of a single crystal of BaTiO3 are simultaneously captured on sub-nanoseconds and nanoscale within individual ferroelectric domains and across walls. A large emergent photo-induced electric field of up to 20 million volts per meter is discovered in a surface layer of the crystal, which then drives polarization and lattice dynamics that are dramatically dis- tinct in a surface layer versus bulk regions. A dynamical phase-field modeling (DPFM) method is developed that reveals the microscopic origin of these dynamics, leading to GHz polarization and elastic waves travelling in the crystal with sonic speeds and spatially varying frequencies. The ad- vance of spatiotemporal imaging and dynamical modeling tools open opportunities of disentangling ultrafast processes in complex mesoscale structures such as ferroelectric domains

We report on a novel nanoparticle platform by electric field assisted assembly, which is capable of manipulating the refractive index distribution through controlling the particle assembly. Two examples based on the control of the scattering properties are presented. We demonstrate lensless imaging in such a system. In addition, we show that random lasing can be enhanced by assembly of anisotropic particles immersed in a gain medium. These examples illustrate that particle assembly technique provides a promising platform for reconfigurable optical applications.

The fluorescence emission spectrum of band-shifting imaging probes can shift under different excitation wavelengths. This unique property may be leveraged to enable chromatic encoding in two-photon imaging. Characterization of the band shifting spectral property under two-photon excitation and preliminary imaging studies will be presented.

In non-degenerate 2-photon excitation (ND-2PE) microscopy, a fluorophore simultaneously absorbs two photons of different energies. We performed a ND-2PE study of fluorescent proteins and synthetic dyes (eg.eGFP, FITC, and etc.) continuously varying energies and numbers of both photons to create two-dimensional map of fluorescence landscapes. By using the best photon energy combination from our two-dimensional map, we found an increase in detected fluorescent image brightness with ND-2PE as we imaged cortical neurons labeled with enhanced green fluorescent protein (eGFP). It should be noted that the photons corresponding to longer wavelength will penetrate deeper into the tissue at reduced scattering. Additionally, using non-overlapping spatial modes carrying the photons at different energies will significantly reduce out of focus fluorescence from the large number of low energy photons, and by a proper choice of the number of high energy photons the ND-2PE fluorescence can be obtained from deep tissue. Experimentally, we strategically displaced two laser beams until they reached the sample plane such that the unwanted background in the excitation beam path was suppressed. In contrast, these two pump beams were well overlapped at focus which still produced sufficient number fluorescence photons for detection. In our experiment, the temporal alignment was achieved with optical delay line in the optical path of IR beam. With this technique we demonstrated experimentally that ND-2PE with side-by-side beams provided a better signal to background ratio in the scattering phantom as compared with D-2PE. The excitation volume of ND-2PE with side-by-side beam was also investigated and determined to be comparable in size with that of the D-2PE.

High-resolution imaging in thick biological tissues beyond a few transport mean free path of photons remains a formidable challenge to modern science and technology. Recent advancements in optical tomography have enabled the reconstruction of the three-dimensional (3D) refractive index distribution in biological samples, which is crucial in the prediction of light propagation in that sample. Here we propose a new technique for imaging second harmonic radiating imaging probes (SHRIMPs) through a tissue using harmonic holography based on the extracted refractive index map. We analyze the spatiotemporal intensity distribution of light pulses using a new model that separate scattering by orders (times of deflections) and show that wide-field excitation and detection of the SHG in tissues beyond one cm thickness is possible with resonant nonlinear plasmonic nanocavities as the SHRIMP. We demonstrate with numerical simulations that the 3D image of SHRIMPs can be extracted by matching the measured second harmonic speckle pattern with that predicted for each point in the sample given the refractive index. We analyze the impact of measurement error in the refractive index on the SNR of the recovered image. We further discuss the influence of the frequency-domain memory effect.

Mid-infrared spectroscopy and imaging has attracted significant interest due to the presence of characteristic vibrational resonances of numerous molecular compounds in the fingerprint region. However, the imaging resolution in the midinfrared can be significantly weakened by the relatively large spot sizes of the beam used to target the absorption resonances of the sample. Photothermal spectroscopy and imaging as a label-free and nondestructive technique has shown great potential for pushing the imaging resolution to values below the mid-infrared diffraction limit while offering enhanced chemical sensitivity and specificity. Mid-infrared photothermal spectroscopy relies on a pump-probe setup, in which a shorter wavelength probe (removed from the targeted resonances) is co-aligned with the resonant pump beam. The modulated photothermal signal is then detected by a lock-in amplifier, whose output can provide information on the signal amplitude as well as phase. However, most commonly, amplitude images have been evaluated, without considering the recorded photothermal phase. We will provide a detailed analysis of the mid-infrared photothermal amplitude and phase information from a melamine bead sample embedded in a 2.5 μm-thick 4-Octyl-4’-Cyanobiphenyl (8CB) liquid crystal environment. Studies related to thermal transport phenomena as well as increases in imaging sensitivity will be presented for sub-diffraction limited resolution, label-free imaging. The concept of wavelength optimization to minimize thermal blurring effects at the zerocrossing for the out-of-phase contribution is introduced as a novel approach to enhance spatial resolution and sensitivity in mid-infrared label-free photothermal imaging.

Pump-probe imaging obtains imaging contrast based on relaxation from a photoexcited state. This has been used as a label-free imaging technique for melanin, hemoglobin, carotenoids, and recently, mitochondrial respiratory chain components. Pump-probe provides a unique opportunity for imaging non-fluorescent molecules, which relax very rapidly (within ~ 200 femtoseconds) to a vibrationally-excited, electronic ground state. In practice, pump and probe wavelengths must be selected that provide good separation between molecules of interest. This is essentially an analytical chemistry application of a technique that is more commonly for physical chemistry. Because of this, much of the pump-probe literature on molecules of interest provide data focused on elucidating energy transfer pathways and molecular structure; predicting from these data which pump/probe wavelengths will work best in an analytical scenario is not straightforward. In this presentation, we discuss general features of pump-probe responses of non-fluorescent molecules, with an eye toward pump/probe wavelength selection. We will focus on spectral shifting and broadening that characterize the vibrationally-excited, electronic ground state, and building a simplified transient absorption model to inform imaging experiments. The end goal of this work is to separate respiratory chain heme proteins and their redox states in a label-free manner. This will lead to new methods for probing mitochondrial function with sub-cellular resolution.

High-speed imaging is an indispensable technology for blur-free observation of fast transient dynamics in virtually all areas including science, industry, defense, energy, and medicine. Unfortunately, the frame rates of conventional cameras are significantly constrained by their data transfer bandwidth and onboard storage. We demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 100 billion fps. Compared with existing ultrafast imaging techniques, CUP has a prominent advantage of measuring an x, y, t (x, y, spatial coordinates; t, time) scene with a single camera snapshot, thereby allowing observation of transient events occurring on a time scale down to tens of picoseconds. Thanks to the CUP technology, for the first time, the human can see light pulses on the fly. Because this technology advances the imaging frame rate by orders of magnitude, we now enter a new regime and open new visions. In this talk, I will discuss our recent effort to develop a second-generation CUP system and demonstrate its applications at scales from macroscopic to microscopic. For the first time, we imaged photonic Mach cones and captured “Sonic Boom” of light in action. Moreover, by adapting CUP for microscopy, we enabled two-dimensional fluorescence lifetime imaging at an unprecedented speed. The advantage of CUP recording is that even visually simple systems can be scientifically interesting when they are captured at such a high speed. Given CUP’s capability, we expect it to find widespread applications in both fundamental and applied sciences including biomedical research.

Through spatial frequency modulated imaging (SPIFI), multimodal, multiphoton microscopy (MPM) benefits from an extended excitation source without compromising the key performance characteristics afforded by point scanning MPM platforms. For example, the introduction of an in-house custom machined mask, which imparts a spatially distinct, temporal amplitude modulation to the extended excitation source, allows one and two-dimensional images to be captured with single element detection. This enables extended source imaging methods to retain a key feature of the point scanning systems; namely, the ability to image within scattering media, at depth. Further, the range of contrast mechanisms for the extended source techniques presented here are not limited and readily extend to both linear and nonlinear imaging modalities. The SPIFI method developed here enables facile detection of such images with the added benefit of enhanced resolution. Notably, the resolution improvement holds across contrast mechanisms, and is independent of whether the contrast is generated through linear or nonlinear processes. Significantly, phase also comes into play as we present new SPIFI geometries that illustrate the role of phase in strategically controlling the source geometry and/or generating image contrast.

Two-dimensional transition metal dichalcogenides (TMD), such as WS2 and MoS2, have been shown to exhibit large second order optical nonlinearity due to their non-centrosymmetric crystalline symmetry in few odd- and mono-layers, and resonance enhancement. Here we study the second-order nonlinear susceptibility of 2D TMDs through second harmonic generation (SHG) and sum frequency generation (SFG). Using a wavelength-tunable femtosecond laser, we can characterize SHG of TMDs to obtain the second-order nonlinear susceptibility at multiple wavelengths. Along with the experimental studies, theoretical investigation of the second-order nonlinear susceptibility is also performed. With this we explore the estimation of the second-order nonlinear susceptibility of 2D TMD layered materials based on their first-order susceptibility through the experimental and theoretical verification of Miller’s Rule for these materials. Additionally, we characterize the second-order nonlinear susceptibility of 2D TMD alloys through the SFG spectroscopy.

The vibrational sum frequency generation spectroscopy (VSFG), one of the second order nonlinear optical tools, has recently become a versatile characterization probe for the molecular interfaces owing to its unique surface selectivity and submonolayer sensitivity. In the past years, the applications of the VSFG technique have expanded into various research fields including biological sciences, environmental chemistry, heterogeneous catalysis, electrochemistry, and etc. However, the proper interpretation of the VSFG data is not trivia. This is partly due to the complexity of the VSFG selection rules. In addition, the complicated chemical and physical nature of the interfaces also made the straightforward explanation of VSFG data difficult. For example, the air/liquid interface of the water-methanol binary interface is among the first liquid interfaces that have been studied by the VSFG. It has been observed that the VSFG intensities from the methanol molecules first increase then decrease along with the increase of the methanol concentrations, the reason of which has been debated for more than 20 years. In this presentation, we will analyze all of the possible factors and provide the correct explanation for this nomonotonic trend of the VSFG intensities as the function of methanol concentrations. We will also show in this presentation our recent results on the polarization selection rules of VSFG that can be used to interpret the newly observed spectral splitting for the model systems of the biomembrane systems.

Graphene-based electric power generation that converts mechanical energy of flow of ionic droplets over the device surface into electricity has emerged as a promising candidate for blue-energy network. Yet the lack of a microscopic understanding of the underlying mechanism has prevented ability to optimize and control the performance of such devices. This requires information on interfacial structure and charging behavior at the molecular level. Here, we use sum-frequency vibrational spectroscopy (SFVS) to probe the interface of device composed of aqueous solution, graphene and supporting polymer substrate. We discover that the surface dipole layer of the polymer is responsible for ion attraction toward and adsorption at the graphene surface that leads to electricity generation in graphene. Graphene itself does not attract ions and only acts as a conducting sheet for the induced carrier transport. Replacing the polymer by an organic ferroelectric substrate could enhance the efficiency and allow switching of the electricity generation. Our microscopic understanding of the electricity generation process paves the way for the rational design of scalable and more efficient droplet-motion-based energy transducer devices.

The development of Ultrafast Electron Microscopy (UEM) and diffraction (UED) permit the imaging of atomic motion in real time and space. UEM and UED have found a vast range of applications spans chemistry, physics, material science, and biology. The temporal resolution in ultrafast electron imaging, typically on the order of few hundred femtoseconds, is limited by the electron pulse duration and the space charge effect. Hence, imaging the fast motions of electrons remains beyond the reach. Recently, we break the temporal resolution limits in UEM by generating a 30-fs electron pulse exploiting the optical gating approach. The gating technique is based on the electron-laser coupling where the free electrons in the wavepacket exchange energy with the light photons of the laser pulse. In this case, the optical laser pulse acts as a temporal gating for the electrons which gain/loss energy. These electrons are filtered out and generate an electron pulse with a temporal profile similar to the gating laser pulse. The obtained, few tens of femtosecond, temporal resolution opens the door- for the first time- to image the electron dynamics in real time. Moreover, the optical attosecond pulse, which has been demonstrated earlier, eventually will be used to gate the electrons in a sub-femtosecond time window. So, the gated electrons will generate a single isolated attosecond electron pulse. This unique tool will establish the attosecond electron imaging tool which we so-called "Attomicroscopy". Attomicroscopy will enable the imaging of the electron motion, last few hundreds of attosecond to few femtoseconds, in action.

We report on experimental activities on HiRES, a novel ultrafast electron diffraction beamline under development at LBNL. The instrument provides high-flux of relativistic electron pulses with sub-picosecond duration, which are then shaped in transverse and longitudinal phase space producing small spot sizes with femtosecond resolution. Alternatively beam shaping can be used to achieve large lateral coherence lengths for chemical and biological applications.

The photoinduced ring opening of 1,3-cyclohexadiene is a prototypical photo-allowed, ultrafast reaction in agreement with the Woodward-Hoffmann rules. Furthermore, it is a model reaction for the biosynthesis of vitamin D. The reaction mechanism involves coupled dynamics of the electrons and nuclei of the molecule in the vicinity of a conical intersection between the excited state and the ground state. It has been intensively investigated by spectroscopic methods, which were primarily sensitive to transient changes in the electronic structure during internal conversion through a conical intersection between the excited state and the ground state. The corresponding structural dynamics have so far only been investigated by a ultrafast x-ray diffraction study. However, spatial resolution down to bond lengths has not been achieved so far. We have investigated the ring opening by gas phase MeV ultrafast electron diffraction with an unprecedented combination of femtosecond temporal and sub Angstrom spatial resolution. The obtained momentum transfer range allows us to follow transient bond length changes by real space transformation of the experimental dataset. Thus, the experimentally observed structural dynamics can be directly compared to quantum molecular dynamics simulations. We, furthermore, can follow the further structural relaxation of the molecule for several hundred femtoseconds beyond relaxation through the conical intersection with the ground state.

Thanks to non-linear absorption processes, non-ablative femtosecond laser pulses applied to fused silica induce bulk morphological transformations in the material associated with a variety of local changes of physical properties. These structural changes includes locally densified glass matrices, self-organized nanostructures as well as the formation of polymorphic phases. As a direct consequence, the material experiences localized volume variation resulting in either tensile or compressive stress, which intensity and direction are both controlled by the pulse energy and the laser polarization, respectively. Here, we will discuss these laser modifications, both from the viewpoint of stress-states and structural changes induced in the material. In particular, we will show how these controlled states along with this ability to tune material properties can be used for novel applications in optomechanics, such as tunable Duffing oscillators, embedded optical wave plates, but also, as a means to investigate mechanical properties at the small scales and for the packaging of complex optical devices.

We show that a multimode fiber can be used to deliver shaped light, either continuous wave or ultra fast pulses, in a resin in order to build useful complex three dimensional objects in areas difficult or impossible to reach with conventional manufacturing tools. We show complex objects that are made by additive manufacturing with either a single photon or a 2 photon process. We investigate the build volume and resolution that are possible by engineering the fiber tip.

Ultrafast laser sources with both high average power and high peak powers at a high repetition rate have many important applications in areas such as high-harmonic generation (HHG), micromachining, and high power optical parametric amplification. In recent years, with the development of high power fiber laser technology, the output of femtosecond fiber laser systems has reached average powers of thousands of watts and peak powers of several gigawatts. However, the pulse duration and pulse energy is limited by the accumulated nonlinear phase in the nonlinear propagation in the fiber, since it will distort the pulse shape and even break the femtosecond pulses. To enhance the performance of femtosecond fiber laser, the nonlinear phase accumulation and compensation is most important optimization factor. Pulse propagation dynamics control is the important method in femtosecond fiber system. This talk will demonstrate the few-cycle laser pulse generation in fiber system with nonlinear process manipulation.

Resolution enhancement of terahertz (THz) imaging is one of central concerns in the THz science and technology research. Because of the used long wavelength (1 THz = 300 um), THz imaging’s resolution is generally in the scale of millimetre. This constitutes a major obstacle for the application of THz imaging in bio-medical diagnosis and semiconductor device inspection [1-3]. Here, we report on a novel sub-wavelength THz imaging method via the femtosecond laser filament in air, which refers to the plasma channel created by a femtosecond laser pulse [4]. A two-color (1 kHz, 50 fs, 1 mJ/pulse, 800 nm + 400 nm) laser filament was created at the focus of the lens (f = 30 cm). The generated THz pulse was detected by a standard electric-optic sampling (EOS) setup [5]. Using the generated THz beam as the probe, near field THz imaging can be obtained. As compared with the image of the sample under optical microscope (resolution: 5 um), no significant blurring effect could be noticed the corresponding scanning THz image . Furthermore, the knife-edge method [6] was applied to measure the THz beam diameter at different positions z. The obtained results indicates taht the diameter of the THz beam varies from 20 um to 50 um. This phenomenon makes a novel sub-wavelength THz imaging technique feasible as we have demonstrated [4]. Further study has revealed that due to the inhomogeneous refractive index distribution inside the femtosecond laser filament, a THz waveguide is created, confining the THz wave energy strongly within a μm scale space. Rely on this new phenomenon, subwavelength resolution THz imaging and high THz wave amplitude could be achieved [7, 8]. References [1] M. Tonouchi, “Cutting-edge terahertz technology,” Nat. Photonics 1, 97-105 (2007). [2] X. C. Zhang, “Terahertz wave imaging: horizons and hurdles,” Phys. Med. Biol. 47, 3667 (2002). [3] R. Inoue et al. “Scanning probe laser terahertz emission microscopy system,” Jpn. J. Appl. Phys. 45, L824-L826 (2006). [4] C. D Amico et al. “Conical forward THz emission from femtosecond-laser-beam filamentation in air,” Phys. Rev. Lett. 98, 235002 (2007). [5] Y. Zhang et al. “Non-radially polarized THz pulse emitted from femtosecond laser filament in air,” Opt. Express 16, 15483-15488 (2008). [6] J. Zhao, et al., "Terahertz imaging with sub-wavelength resolution by femtosecond laser filament in air", Scientific Reports 4, 3880 (2014) [7] J. Zhao, et al., " Propagation of terahertz wave inside femtosecond laser filament in air", Laser Phys. Lett. 11, 095302 (2014) [8]J. Zhao, et al., " Strong Spatial Confinement of Terahertz Wave inside Femtosecond Laser Filamen"t, ACS Photonics, 2338–2343, 3 (2016)

Precisely detecting and controlling time jitter of femtosecond laser pulse train can enable high resolution phase measurement by using time of flight (TOF) scheme. In this presentation, we will introduce our recent progresses on precision surface metrology and phase imaging by utilizing high resolution synchronization between radio frequency reference source and femtosecond laser pulse train generated in a passively mode locked fiber laser.

The discovery of soft structures in dinosaur bone with the morphological and molecular characteristics of blood vessels in extant vertebrates was both surprising and controversial. Mounting evidence suggests that these soft tissues are blood vessels, their preservation driven in part by reactive oxygen species derived from hemoglobin degradation. More data are needed to support this hypothesis. Raman spectroscopy, and resonance Raman in particular, can provide detailed information as to the chemical makeup of these samples. We used two different excitation wavelengths in microscale Raman measurements to look for lines characteristic of degraded heme molecules, both in ancient vessels and modern analogues taken from semi-fossilized, hemoglobin-soaked ostrich bones. In both samples, we observed two regimes: dark colored, stiff regions and more transparent, elastic regions. We discovered that the two apparent regimes in the samples had different strengths of Raman returns, and that resonance effects greatly affected the Raman intensity. In all cases, there was some evidence of degraded heme spectra, though the increased returns indicated that the dark regimes had reacted more strongly with the heme specie. The modern vessels displayed a resonance Raman intensity consistent with hemoglobin molecular structures, which indicated resonance spectra would provide understanding of the ancient heme molecule. To investigate the two regimes more thoroughly, we acquired Raman spectra over areas where the sample transitioned from one regime to another. Variable wavelength resonance Raman measurements over the whole sample were used to give more information about the heme species present, in both ancient and modern samples.

The health and growth rates of shellfish depends critically on the precise chemical and biological makeup of the surrounding seawater. Rapid and continuous sensing of the marine environment enables improved harvests and better profits. However, underwater spectroscopy is still in its infancy. Our research aim is to develop a new sensor that is well-suited for marine environments and one that is capable of working at depths of up to 20 metres. We discuss a modified high intensity femtosecond coherent anti-Stokes Raman Scattering (CARS) system, which removes the usual limitations such as a limited wavenumber range and a low signal-to-noise ratio (SNR) due to non-resonant background. A particular set of Probe and Stokes pulses aim to investigate the spectra of various living plankton in seawater. It also determines critical parameters for the underwater CARS system such as signal dependent on the pulse energies, vibrational dephasing times and numerical aperture dependencies in forward CARS. This links to theory and greatly expands the understanding of CARS parameters for future underwater CARS experiments.

Identification of microorganisms using Laser Induced Breakdown Spectroscopy (LIBS) is currently an experimental technique in the early development stage. The highly expensive and complex instrumentation involved in this technique is a severe limitation to its translation into a commercial diagnostic device. In this study, we have investigated the efficacy of using low cost, non-intensified and portable CCD spectrometer systems for identification and discrimination of microorganisms, such as species of gram-positive (Staphylococcus aureus) and gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae) using their spectral fingerprint. Comparison of the resulting emission spectra from these detectors, on ablation using nanosecond pulsed Nd: YAG (1064 nm) laser source has been carried out. We have established the efficiency of classification for discrimination between gram-positive and gram-negative bacteria and also between 2 different species of gram negative bacteria. We also present the results of ablation of the microbial smears on several organic as well as inorganic substrates and their relative efficiency in identification of the microbial species. The results indicate the feasibility of porting this technique onto a PDMS (Polydimethylsiloxane) or paper based microfluidic point of care device which can eliminate the complex sample preparation steps required currently. This study has huge potential for the development of a low-cost commercial LIBS based microfluidic device for detection of microorganisms.

In this in vivo pilot clinical trial, an estimation of NIR spectral features of malignant and benign tumors and normal skin was carried out. The human tissue spectra simultaneously including Raman spectroscopy and autofluorescence signals were registered using the portable spectroscopic equipment with 785 nm excitation laser and spectra registration in the 800-950 nm area. Spectral data were analyzed using PLS-DA method extracted the relevant information that allow for classification of skin neoplasm type. The most important spectral bands were found with the variable importance in projection analysis. We analyzed four models: basal cell carcinoma versus normal skin, basal cell carcinoma versus benign tumors, basal cell carcinoma versus melanoma and malignant tumors versus normal skin and benign neoplasms. The results of the neoplasm groups differentiating for each model were presented by using boxplot diagrams and receiving operating characteristic (ROC) curve approach. Achieved results demonstrate high accuracy of Raman spectroscopy and autofluorescence combination in NIR for the classification of malignant and benign skin lesions.

In this research, the influence of pulse width and energy on the nonlinear refractive index (n₂) and nonlinear absorption (β) in Multiwalled carbon- nanotubes (MWCNTs) were experimentally studied. For this purpose, three different MWCNTs concentrations were used and were dispersed in a Polyvinyl alcohol (PVA) solution. We found a highly dependence of n₂ and β with the MWCNTs concentration, optical intensity, and pulse width.