We present a reversible reaction-based Raman probe for live-cell imaging of Glutathione (GSH) by the hyperspectral stimulated Raman scattering microscopy. By introducing a cyano group as the Raman reporter and an alkyne group as the internal standard, we have designed, synthesized, and characterized a series of Raman-based probes for ratiometric imaging and quantification of GSH levels in living cells and organisms.
Saturated fatty acids (sFA) are more toxic to cells than unsaturated fatty acids (uFA). Previously, we developed a chemical imaging strategy to track the spatiotemporal dynamics of specific deuterium-labeled fatty acids in living Caenorhabditis elegans, called isotope-labeling coupled stimulated Raman scattering (iSRS) microscopy, and showed that sFAs are incorporated into lipid droplets (LDs) slower than uFAs. To study how fatty acids are integrated into LDs at different rates, we performed a high-throughput forward genetic screen using iSRS microscopy and identified mutants with enhanced sFA integration into LDs. Currently, we are sequencing these candidates to identify the molecular players in fatty acid metabolism and lipotoxicity.
We systematically investigate the changes of lipid and protein contents at all developmental stages of Caenorhabditis elegans, including L1 to L4 larvae, and adults, using the recently developed hyperspectral stimulated Raman scattering (hsSRS) microscopy. The gut granules in larvae, which are known as lysosome-like organelles, are specifically identified and the temporal change of these gut granules are tracked at different stages. By acquiring the spectral images of C. elegans at different ages and analyzing the lipid spectra change statistically with hsSRS, we will foster a better understanding of the physiological and pathophysiological processes in living organisms.
High-speed label-free imaging with chemical contrast is effective for non-invasive analysis of the metabolic heterogeneity of single cells. Stimulated Raman scattering (SRS) microscopy enables high-speed label-free image acquisition with molecular vibrational specificity. While single-color SRS microscopy only acquires images at a certain vibrational frequency, multicolor SRS microscopy successively acquires SRS images at different vibrational frequencies, which then can be used to investigate the distributions of different intracellular molecules. However, its imaging speed remains an order of magnitude slower than that of single-color video-rate SRS microscopy. Previous approaches to circumvent this issue used either only two colors with limited chemical specificity or multiplex detection of SRS spectra using a photodiode array at the expense of imaging speed. Here we demonstrate high-speed four-color SRS imaging using a single photodiode by introducing fast wavelength-switched laser pulses. The fast wavelength switching is realized by the use of an optical intensity modulator as a time gate, a diffraction grating, and fiber delay lines. Using the developed system, we demonstrate motion-artifact-free multicolor SRS imaging of polymer beads and living cells. The results firmly support that our method is a powerful tool for the label-free analysis of living cells in microbiology, oncology, plant science, and medicine.
We experimentally investigate mid-infrared (MIR) supercontinuum (SC) generation in chalcogenide step-index optical fibers. The pump source is generated by the difference frequency generation with a pulse width of ~170 fs, a repetition rate of ~1000 Hz, and a wavelength range tunable from 2.5 to 11 μm. The wide MIR SC will be applied in sensing, medical and biological imaging areas.
We report the manufacturing and characterization of Tellurite micro structured fibres (MOFs) with low OH content. The different purification processes used during the fabrication of the TeO2 - ZnO - Na2O glass allowed us to reduce the hydroxyl compounds concentration down to 1ppm mass. A suspended core MOF was drawn from this material and then pumped by nanojoule-level femtosecond pulses at 1.7μm, its zero dispersion wavelength (ZDW), and well above it at 2.5μm. We show the related supercontinuum (SC) generated in the two distinct dispersion regimes of the waveguide. Moreover, the SC spanning was extended in both visible and mid-IR regions (between 600nm up to 3300nm) by the taperisation of the previously tested MOFs.
Nonlinear optical polymers show promising potential applications in photonics, for example, electro-optical devices. Poly (methyl methacrylate) (PMMA) is widely used in optical waveguides, integrated optics and optical fibers. However, PMMA has not been used for nonlinear optical waveguides since it has a low nonlinear refractive index. We successfully prepared chalcogenide amorphous nanoparticles doped PMMA that had a high nonlinearity. The As3S7 bulk glass was dissolved in propylamine to form a cluster solution. Then the As3S7/propylamine solution was added into methyl methacrylate (MMA) containing photoinitiator Irgacure 184 about 0.5 wt%. After well mixing the As3S7 nanoparticle doped MMA was transparent. Under the irradiation by a 365 nm UV lamp, As3S7 nanoparticles doped PMMA was obtained with yellow color. The third-order nonlinear optical susceptibility of As3S7 nanoparticles doped PMMA was investigated. An optical waveguide array based on the As3S7 nanoparticles doped PMMA composite of high nonlinearity was fabricated.
We present the broad and ultra-flat optical parametric gain in the highly nonlinear tellurite fibers with tailored chromatic dispersion. The effect of pump wavelengths and powers on dual-pump configuration of four-wave mixing (FWM) are investigated. It is clarified that an ultra-flat gain bandwidth with 658 nm and ±0.01 dB fluctuation can be achieved at the dual-pumping power of 1.25 W. Moreover, a gain bandwidth with 1524 nm and 60 dB signal gain with gain ripples can be obtained at the dual-pumping power of 3.0 W in 25 cm-long hybrid tellurite microstructured optical fiber.
Widely wavelength tunable soliton self-frequency shift (SSFS) from 1.58 μm to 2.07 μm was experimentally demonstrated in a highly nonlinear fiber pumped with a mode-locked sub-100 fs Er-doped fiber laser. The maximum output spectrum (full width at half maximum, FWHM) around 2 μm is 143 nm. Although the pulse width of SSFS was measured to be a few picoseconds, the large FWHM bandwidth of SSFS spectrum shows that soliton with sub-50 fs could be achieved if the giant chirped pulse is efficiently re-compressed to be transforms limited. Dispersive wave with a minimum pulse width of 50 fs was also observed.
We report here flattened supercontinuum (SC) generated in tellurite-phosphate and chalcogenide-tellurite hybrid microstructured optical fibers (HMOFs) whose chromatic dispersion spectra are tailored with high freedom due to large refractive index difference (∆n) between the core and cladding glasses. It is shown in the simulation that the tellurite-phosphate HMOF whose chromatic dispersion spectrum is near-zero and flattened with three zero-dispersion wavelengths (ZDWs) over a wide wavelength range from 1000 to 4000 nm is beneficial to obtain broad and flattened SC spectra. By using a large ∆n of 0.49, the tellurite-phosphate HMOF which has flattened chromatic dispersion and three ZDWs is successfully fabricated. When a 20-cm-long tellurite-phosphate HMOF is pumped at 1550 nm with a 1560-W peak power, an SC extended from ~800 to 2400 nm where ~5-dB spectral flatness in the wavelength ranges from 890 to 1425 nm and from 1875 to 2400 nm (~1060-nm bandwidth in total) is observed. In addition, a flattened SC spectrum with ~6-dB spectral flatness over a broad wavelength range from 950 to 3350 nm (2400-nm bandwidth in total) is generated by pumping a 1-cm-long chalcogenide-tellurite HMOF at 2300 nm with a 40-MW peak power.
A novel highly nonlinear three-core chalcogenide-tellurite fiber is proposed and fabricated in the paper. Each core
with high index is made of chalcogenide glass (Ge15Ga3Sb13S69). The background with low index is made of TeO2–ZnO–Li2O–Bi2O3 (TZLB) glass. Each core of this fiber can be considered as a single core. And it can be used for the high power transmission. The effective modal refractive index and the chromatic dispersion are calculated with the light beam coupled in one core of the fiber, respectively. Supercontinuum generation from 1400 nm to 3536 nm in this fiber is investigated under the pump of a 2200 nm femtosecond fiber laser.
Alternative materials to silica glass are necessary for supercontinuum (SC) generation at longer wavelengths in the midinfrared
(MIR) region. The alternative materials should possess the properties of wide transmission window and high
nonlinearity, simultaneously. Chalcogenide glass is the suitable candidate due to its excellent properties of transmission
and nonlinearity in MIR region. In this paper, we demonstrate the SC generation in a suspended-core As2S3 chalcogenide microstructured optical fiber (MOF). The variation of SC is investigated by changing the fiber length, pump peak power and pump wavelength. In the case of long fibers (20 and 40 cm), the SC ranges are discontinuous and stop at the
wavelengths shorter than 3500 nm, due to fiber absorption. In the case of short fiber as 2.4 cm, the SC range is continuous and can extend to the wavelengths longer than 4 μm. The process of SC broadening is observed when the pump peak power increases from 0.24 to 1.32 kW at 2500 nm in the 2.4 cm long fiber. The variation of SC range with the pump wavelength changing from 2200 to 2600 nm is studied. The selected wavelengths correspond to the dispersion of As2S3 MOF from the normal to anomalous region. The SC generation is simulated by the generalized nonlinear Schrödinger equation. The simulation includes the SC difference between 1.3 and 2.4 cm long fiber at 2500 nm pumping and the variation of SC with pump peak power in 2.4 cm long fiber. The simulation agrees well with the experiment.
Superluminal propagation at negative group velocity was demonstrated in a highly nonlinear fiber embedded in a
Brillouin laser ring cavity. A maximum advancement of 369 ns and strong Stokes lasing power of 482 mW were
achieved when the cavity was pumped with a 1 MHz sinusoidal wave modulated signal at power level of 1 W. The
frequency dependence of fast light in this fiber ring cavity was examined with modulation frequencies of 1 kHz to 15
MHz. a maximum fractional advancement of 0.54 was achieved at 10 kHz and a maximum negative group index of -
9480 was demonstrated at 1 kHz.
The dependence of chromatic dispersion of tellurite microstructured optical fiber on composition and structure was investigated. The material dispersion is mainly dependent on material composition of core glass. And the waveguide dispersion of fiber mainly depends on refractive index distribution in cross-section. The radial step of refractive index produces a peak in waveguide dispersion curve whose value and position are related to both contrast of refractive index and its position. Based on this guidance, some particular dispersion profiles were designed in tellurite fibers.
Supercontinuum (SC) generation from a highly nonlinear tellurite microstructured fiber with multi-ring holes was demonstrated by pumping with a 2 μm high power mode-locked fiber laser. The chromatic dispersion of the fiber was measured with a homemade white-light spectral interferometer on a wide wavelength range and matched very well with the theoretical calculation. The zero dispersion wavelength (ZDW) of the fiber was measured to be 1358 nm and calculated to be 1390 nm. Although the pumped wavelength was far away from ZDW, with flat dispersion profile of the fiber on the anomalous dispersion, the SC could be expanded from 650 nm to 2850 nm with launched pulse energy of several hundred picojoules. Simulations of SC generation were performed and showed fair agreement with the experimental results.
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