Detecting spatio-temporal urban surface changes using identified temporary coherent scatterers

Synthetic aperture radar(SAR) is able to detect surface changes in urban areas with a short revisit time, showing its capability in disaster assessment and urbanization monitoring.Most presented change detection methods are conducted using couples of SAR amplitude images. However, a prior date of surface change is required to select a feasible image pair. We propose an automatic spatio-temporal change detection method by identifying the temporary coherent scatterers. Based on amplitude time series, χ^(2)-test and iterative single pixel change detection are proposed to identify all step-times: the moments of the surface change. Then the parameters, e.g., deformation velocity and relative height, are estimated and corresponding coherent periods are identified by using interferometric phase time series. With identified temporary coherent scatterers, different types of temporal surface changes can be classified using the location of the coherent periods and spatial significant changes are identified combining point density and F values. The main advantage of our method is automatically detecting spatio-temporal surface changes without prior information. Experimental results by the proposed method show that both appearing and disappearing buildings with their step-times are successfully identified and results by ascending and descending SAR images show a good agreement.

Coherent Raman scattering imaging of lipid metabolism in cancer

Cancer cells dysregulate lipid metabolism to accelerate energy production and biomolecule synthesis for rapid growth.Lipid metabolism is highly dynamic and intrinsically heterogeneous at the single cell level.Although°uorescence microscopy has been commonly used for cancer research,bulky°uorescent probes can hardly label small lipid molecules without perturbing their biological activities.Such a challenge can be overcome by coherent Raman scattering(CRS)microscopy,which is capable of chemically selective,highly sensitive,submicron resolution and high-speed imaging of lipid molecules in single live cells without any labeling.Recently developed hyperspectral and multiplex CRS microscopy enables quantitative mapping of various lipid metabolites in situ.Further incorporation of CRS microscopy with Raman tags greatly increases molecular selectivity based on the distinct Raman peaks well separated from the endogenous cellular background.Owing to these unique advantages,CRS microscopy sheds new insights into the role of lipid metabolism in cancer development and progression.This review focuses on the latest applications of CRS microscopy in the study of lipid metabolism in cancer.

Simultaneous measurements of global vibrational spectra and dephasing times of molecular vibrational modes by broadband time-resolved coherent anti-Stokes Raman scattering spectrography

In broadband coherent anti-Stokes Raman scattering （CARS） spectroscopy with supercontinuum （SC）, the simultaneously detectable spectral coverage is limited by the spectral continuity and the simultaneity of various spectral components of SC in an enough bandwidth. By numerical simulations, the optimal experimental conditions for improving the SC are obtained. The broadband time-resolved CARS spectrography based on the SC with required temporal and spectral distributions is realised. The global molecular vibrational spectrum with well suppressed nonresonant background noise can be obtained in a single measurement. At the same time, the measurements of dephasing times of various molecular vibrational modes can be conveniently achieved from intensities of a sequence of time-resolved CARS signals. It will be more helpful to provide a complete picture of molecular vibrations, and to exhibit a potential to understand not only both the solvent dynamics and the solute-solvent interactions, but also the mechanisms of chemical reactions in the fields of biology, chemistry and material science.

Selective excitation of molecular mode in a mixture by femtosecond resonance-enhanced coherent anti-Stokes Raman scattering spectroscopy

Femtosecond time-resolved coherent anti-Stokes Raman scattering （CARS） spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this broad spectroscopy. However, it can be demonstrated that by the electronic resonance enhancement optimization control a selective excitation of specific vibrational mode is possible. Using an electronically resonance-enhanced effect, iodine molecule specific CARS spectroscopy can be obtained from a mixture of iodine-air at room temperature and a pressure of 1 atm （corresponding to a saturation iodine vapour as low as about 35 Pa）. The dynamics on either the electronically excited state or the ground state of iodine molecules obtained is consistent with previous studies （vacuum, heated and pure iodine） in the femtoseeond time resolved CARS spectroscopy, showing that an effective method of suppressing the non-resonant CARS background and other interferences is demonstrated.

Selective excitation and suppression of coherent anti-Stokes Raman scattering by shaping femtosecond pulses

Femtosecond coherent anti-Stokes Raman scattering （CARS） suffers from poor selectivity between neighbouring Raman levels due to the large bandwidth of the femtosecond pulses. This paper provides a new method to realize the selective excitation and suppression of femtosecond CARS by manipulating both the probe and pump （or Stokes） spectra. These theoretical results indicate that the CARS signals between neighbouring Raman levels are differentiated from their indistinguishable femtosecond CARS spectra by tailoring the probe spectrum, and then their selective excitation and suppression can be realized by supplementally manipulating the pump （or Stokes） spectrum with the π spectral phase step.

Coherent coupling between vibrational modes of C-H bonds at different positions studied by femtosecond time-resolved coherent anti-Stokes Raman scattering

We performed femtosecond time-resolved coherent anti-Stokes Raman scattering （fs-CARS） measurements on liquid toluene and PVK film. For both samples, we selectively excited the CH stretching vibrational modes and observed the expected quantum beat signals. The frequency of the well-defined beats is in good agreement with the energy difference between the two simultaneously excited modes, which demonstrates that a coherent coupling between the vibrational modes of the C H chemical bonds exists at the different positions of the molecules. The dephasing times of the excited modes are obtained simultaneously.

High-resolution imaging of graphene by tip-enhanced coherent anti-Stokes Raman scattering

Coherent anti-Stokes Raman scattering(CARS)is able to enhance molecular signals by vibrational coherence compared to weak Raman signal.The surface or tip enhancement are successful technologies,which make it possible for Raman to detect single molecule with nanometer resolution.However,due to technical diffculties,tip-enhanced CARS(TECARS)is not as successful as expected.For single molecular detection,high sensitivity and resolution are two main challenges.Here,we reported the first single atom layer TECARS imaging on Graphene with the highest resolution about 20 nm,which has ever been reported.The highest EF_(TECARS/CARS) is about 10^(4),the similar order of magnitude with SECARS(EF of tip is usually smaller than that of substrates).Such resolution and sensitivity is promising for medical,biology and chemical applications in the future.

COHERENT ANTI-STOKES RAMAN SCATTERING MICROSCOPY TO MONITOR DRUG DISSOLUTION IN DIFFERENT ORAL PHARMACEUTICAL TABLETS

Coherent anti-Stokes Raman scattering(CARS)microscopy is used to visualize the release of a model drug(theophylline)from a lipid(tripalmitin)based tablet during dissolution.The effects of transformation and dissolution of the drug are imaged in real time.This study reveals that the manufacturing process causes significant differences in the release process:tablets prepared from powder show formation of theophylline monohydrate on the surface which prevents a controlled drug release,whereas solid lipid extrudates did not show formation of monohydrate.This visualization technique can aid future tablet design.

Wide-Field Vibrational Phase Contrast Imaging Based on Coherent Anti-Stokes Raman Scattering Holography

We propose and implement a wide-field vibrational phase contrast detection to obtain imaging of imaginary components of third-order nonlinear susceptibility in a coherent anti-Stokes Raman scattering （CARS） microscope with full suppression of the non-resonant background. This technique is based on the unique ability of recovering the phase of the generated CARS signal based on holographic recording. By capturing the phase distributions of the generated CARS field from the sample and from the environment under resonant illumination, we demonstrate the retrieval of imaginary components in the CARS microscope and achieve background free coherent Raman imaging.

Theoretical and experimental investigations of coherent phonon dynamics in sapphire crystal using femto-second time-resolved coherent anti-Stokes Raman scattering

We report on the theoretical and the experimental investigations of the coherent phonon dynamics in sapphire crystal using the femtosecond time-resolved coherent anti-Stokes Raman scattering （fs-CARS） technique. The temporal chirped white-light continuum （WLC） is used for the Stokes pulse, therefore we can perform the selective excitation of the phonon modes without using a complicated laser system. The expected quantum beat phenomenon is clearly observed. The theoretical formulas consist very well with the experimental results. The dephasing times of the excited phonon modes, the wavenumber difference, and the phase shift between the simultaneously excited modes are obtained and discussed. This work opens up a way to study directly high-frequency coherent phonon dynamics in bulk crystals on a femtosecond time scale and is especially helpful for understanding the nature of coherent phonons.

Analysis of detection limit to time-resolved coherent anti-Stokes Raman scattering nanoscopy

In the implementation of CARS nanoscopy, signal strength decreases with focal volume size decreasing. A crucial problem that remains to be solved is whether the reduced signal generated in the suppressed focal volume can be detected. Here reported is a theoretical analysis of detection limit （DL） to time-resolved CARS （T-CARS） nanoscopy based on our proposed additional probe-beam-induced phonon depletion （APIPD） method for the low concentration samples. In order to acquire a detailed shot-noise limited signal-to-noise （SNR） and the involved parameters to evaluate DL, the T-CARS process is described with full quantum theory to estimate the extreme power density levels of the pump and Stokes beams determined by saturation behavior of coherent phonons, which are both actually on the order of ~ 109 W/cm2. When the pump and Stokes intensities reach such values and the total intensity of the excitation beams arrives at a maximum tolerable by most biological samples in a certain suppressed focal volume （40-nm suppressed focal scale in APIPD method）, the DL correspondingly varies with exposure time, for example, DL values are 103 and 102 when exposure times are 20 ms and 200 ms respectively.

Supercontinuum fiber laser-based coherent anti-Stokes Raman scattering microscopy for label-free chemical imaging

Coherent anti-Stokes Raman scattering(CA RS)microscopy can resolve the chemical compo-nents and distribution of living biological systems in a label-firee manner and is favored in several disciplines.Current CA RS microscopes typically use bulky,high-performance solid-state lasers,which are expensive and sensitive to environmental changes.With their relatively low cost and environmental sensitivity,supercontinum fiber(SF)lasers with a small footprint have found increasing use in biomedical applications.Upon these features,in this paper,we homebuilt a low-cost CARS microscope based on a SF laser module(scCA RS microscope).This SF laser module is specially customized by adding a time synchronized seed source channel to the SF laser to form a dual-channel output laser.The performance of the scCARS microscope is evaluated with dimethyl sulfoxide,whose results confirm a spatial resolution of better than 500nm and a detection sensitivity of millimolar concentrations.The dual-color imaging capability is further demonstrated by imaging different species of mixed microspheres.We finally explore the potential of our scCARS microscope by mapping lipid droplets in different cancer cells and corneal stromal lenses.

Nonlinear optical microscopy for skin in vivo:Basics,development and applications

Multi-photon microscopy(MPM)and coherent anti-Stokes Raman scattering(CARS)are two advanced nonlinear optical imaging techniques,which provide complementary information and have great potential in combination for noninvasive in vrito biomedical applications.This paper provides a detailed discussion of the basics,development and applications of these technologies for in vrivo skin research,covering the following topics:The principle and advantage of MPM and CARS,instrumentation development for in vino applications,MPM and CARS of normal skin,application of MPM and CARS in skin cancer and disease diagnosis;application of MPM in skin disease intervention,ie.,imaging guided two-photon photothermolysis.

Stimulated Raman scattering microscopy on biological cellular machinery

Beneting from the developments of advanced optical microscopy techniques,the mysteries of biological functions at the cellular and subcellular levels have been continuously revealed.Stimulated Raman scattering(SRS)microscopy is a rapidly growing technique that has attracted broad attentions and become a powerful tool for biology and biomedicine,largely thanks to its chemical specicity,high sensitivity and fast image speed.This review paper introduces the principles of SRS,discusses the technical developments and implementations of SRS microscopy,then highlights and summarizes its applications on biological cellular machinery andnally shares our visions of potential breakthroughs in the future.

Stimulated Raman scattering microscopy for rapid brain tumor histology

Rapid histology of brain tissues with sufficient diagnostic information has the great potential to aid neurosurgons during operations.Stimulated Raman Scattering(SRS)microscopy is an emerging label-free imaging technique,with the intrinsic chemical resolutions to delineate brain tumors from normal tissues without the nood of time-consuming tissue processing.Growing number of studies have shown SRS as a“virtual histology"tool for rapid diagnosis of various types of brain tumors.In this review,we focus on the basic principles and current developments of SRS microscopy,as well as its applications for brain tumor imaging.

NON-LINEAR OPTICAL IMAGING OF OBESITY-RELATED HEALTH RISKS:REVIEW

This review highlights the recent applications of non-linear optical(NLO)microscopy to study obesity-related health risks.A strong emphasis is given to the applications of coherent anti-Stokes Raman scattering(CARS)microscopy where multiple non-linear optical imaging modalities including CARS,sum-frequency generation(SFG),and two-photon fluorescence are employed simultaneously on a single microscope platform.Specific examples on applications of NLO microscopy to study lipid-droplet biology,obesity-cancer relationship,atherosclerosis,and lipidrich biological structures are discussed.

High Wavenumber Density Fluctuation Measurement in the HT-7 Tokamak

A three channel CO2 laser forward scattering diagnostic system was set up to study the core plasma density fluctuation in the HT-7 tokamak. The range of the wavenumber measurement in the poloidal direction was kθ= 12 cm^-1 to 34 cm^-1 and the wavenumber resolution was △k = 2.5 cm^-1. The wavenumber spectrum, the coexisting modes and the micro-instability eruption in experiments are presented.

Scanning the energy dissipation process of energetic materials based on excited state relaxation and vibration–vibration coupling

The energy dissipation mechanism of energetic materials（EMs） is very important for keeping safety. We choose nitrobenzene as a model of EM and employ transient absorption（TA） spectroscopy and time-resolved coherent anti-stokes Raman scattering（CARS） to clarify its energy dissipation mechanism. The TA data confirms that the excited nitrobenzene spends about 16 ps finishing the twist intramolecular charge transfer from benzene to nitro group, and dissipates its energy through the rapid vibration relaxation in the initial excited state. And then the dynamics of vibrational modes（VMs） in the ground state of nitrobenzene, which are located at 682 cm^-1（v1）, 854 cm^-1（v2）, 1006 cm^-1（v3）, and 1023 cm^-1（v4）,is scanned by CARS. It exhibits that the excess energy of nitrobenzene on the ground state would further dissipate through intramolecular vibrational redistribution based on the vibrational cooling of vi and v2 modes, v1 and v4 modes, and v3 and v4 modes. Moreover, the vibration-vibration coupling depends not only on the energy levels of VMs, but also on the spatial position of chemical bonds relative to the VM.

Investigation of Changes in the Fine Structure of Graphitizing Carbon Materials during Heat Treatment by X-Ray Diffraction Analysis

The properties of synthetic graphite materials, widely used in advanced fields, are determined by their structure, which is formed in the process of high-temperature (~2500°C) heat treatment. The fine structure of a graphitizing carbon material based on petroleum coke containing 1.3 wt% S at various stages of graphitization was studied by X-ray diffraction analysis. Some of the samples contained the addition of dispersed Fe2O3. It is shown that the heat-treated material in the range 1200°C - 2600°C is heterogeneous, its component composition is determined by the processing temperature and the presence of Fe2O3 additive. The observed dependence of the component composition on the heat treatment temperature suggests that the process of graphitization of the carbon material, apparently, develops through a number of metastable states.

Phase and Structural Transformation of Polyacrylonitrile Fiber during Two-Stage Thermal Stabilization

The influence of two-stage isothermal treatment on the change in the linear dimensions of the fiber, the average sizes of the coherent scattering regions, the texture and phase composition of the polyacrylonitrile fiber in the process of isothermal thermal stabilization is considered by the methods of dilatometry and X-ray diffraction analysis. It is shown that preliminary short-term heat treatment at a lower temperature affects the process of structural transformations of the polyacrylonitrile fiber material and the formation of a new highly dispersed phase of the thermally stabilized fiber.