Jian-g Chen

Glass-clad Cr4+:YAG crystal fiber for the generation of superwideband amplified spontaneous emission.

Glass-clad Cr4+:YAG crystal fiber is demonstrated by a codrawing laser-heated pedestal growth method. As much as 2.45 mW of superwideband amplified spontaneous emission (ASE) is generated in the optical fiber communication band with a 3-dB width of 240 nm. The simulation indicates that the ASE power could be in excess of 20 dBm for a 5-microm-diameter core at a pump power of 2.5 W.

Broadband emission from Cr-doped fibers fabricated by drawing tower.

We report on the first fabrication of a Cr-doped fiber using a drawing-tower method with Cr:YAG as the core of the preform. Both Cr3+ and Cr4+ ions coexist in the Cr-doped fiber, and the amplified spontaneous emission (ASE) spectrum shows a broadband emission of 1.2 to 1.55 mum which can not be realized by using currently available fiber amplifiers. This indicates that the new Cr-doped fibers have the potential for being used as a broadband fiber amplifier to cover the bandwidth of the entire 1.3-1.6 mum range which exhibit 300 nm usable spectral bands.

400-nm-Bandwidth Emission From a Cr-Doped Glass Fiber

Cr4+-doped glass fiber by a laser-heated pedestal growth method is reported. By analyzing the absorption spectra, the transitions of Cr3+ and Cr4+ in the fibers are identified. With appropriate pumping wavelength and divalent doping concentration, both Cr3+ and Cr4+ emission bands can be excited simultaneously, and become comparable in their fluorescent intensities. As a result, more than 400-nm-width emission peaked at 1144 nm was generated at room temperature. As much as 12muW of amplified spontaneous emission was obtained by pumping with a 900-nm Ti : sapphire laser

Composition dependence of the microspectroscopy of Cr ions in double-clad Cr:YAG crystal fiber

We have demonstrated the use of microspectroscopy for measuring the Cr3+ and Cr4+ fluorescence spectra in double-clad Cr:YAG crystal fiber. The emission spectra of Cr3+ and Cr4+ are detected from core and inner cladding. The Cr3+ spectrum in the inner cladding shows a broad-band emission from 650to950nm, while the emission of Cr4+ occurs in the range of 1.15–1.55μm with a peak around 1.22μm. The characteristic of Cr ion at high-field sites shows a narrow-band emission (E2→A24 for Cr3+; E1→A23 for Cr4+), whereas that at low-field sites shows a broad-band emission (T24→A24 for Cr3+; T23→A23 for Cr4+). The emission intensity ratio of high-field sites to low-field sites in the inner cladding with different compositions has been investigated. It varies from 20% to 29% for Cr3+ and from 7.1% to 11.3% for Cr4+ when the concentration of SiO2 increases from 26.9to43.0wt%.

Photobleaching under single photon and multi-photon excitation: chloroplasts in protoplasts from Arabidopsis thaliana

Abstract Photobleaching as a result of intense laser irradiation has been an important issue in the applications of confocal microscopy. In this study we are employing time-lapsed micro-spectroscopy to compare the effects of photobleaching under single photon and multi-photon excitation. A model is derived to account for photobleaching in both cases and protoplasts from Arabidopsis thaliana are employed as the sample. We have found that multi-photon excitation have impacts on the samples in ways much different from cw illumination in the linear domain.

Micro-spectroscopy of chloroplasts in protoplasts from Arabidopsis thaliana under single- and multi-photon excitations

Ultrafast laser pulses are known to generate impacts on specimens in ways much different from cw illumination in the applications of confocal microscopy. In this study, protoplasts from Arabidopsis thaliana are employed as the samples to compare the effects induced by single- and multi-photon excitations under confocal imaging configuration. Through time-lapsed micro-spectroscopy we are able to characterize the differences in photo-bleaching and the evolution of fluorescence spectra of chloroplasts thus induced. These differences may be attributed to the disruption of chained reaction as a result of multi-photon excitation in photosynthesis.

Optical beam induced current microscopy at DC and radio frequency

Abstract In this paper we introduce the concept of optical beam induced current (OBIC) generation at radio frequencies. The method is combined with lateral raster scanning of a tightly focused spot which configuration results in a technique of high spatial resolution. We demonstrate experimentally that if a pulsed laser is used to excite the sample then the frequency transfer function of the optically active device is readily obtained with at least 1 μm spatial resolution, in real time. In addition, with the help of an appropriate electronic arrangement, we demonstrate how to obtain pseudo-colored OBIC ‘images’ of the sample.

Multiphoton fluorescence spectroscopy of flourescent bioprobes and biomolecules

Multi-photon fluorescence spectra of a number of commonly used biological probes were measured in this study. Significant spectral variation has been detected between single and multi- photon excitation. The result is important for the proper selection of spectral setting/dichroic beam splitter in the set- up of a multi-photon fluorescence microscope. The information can also be useful in the detection of multi-photon fluorescence in bio-chip technology. In addition, we have investigated a few highly fluorescent bio-molecules commonly found in plant cells.

Fabrication of Cr-doped fibers by drawing tower

We report on the first fabrication of a Cr-doped fiber using a drawing-tower method with Cr:YAG as the core of the preform. The Cr-doped fibers have potential for use as fiber amplifier to cover the bandwidths in the whole 1.3-1.6 mum range

Laser scanning microscopy of enamel and dentin sections with two-photon fluorescence and second harmonic generation

In this study, we have demonstrated the use of two-photon fluorescence and second harmonic (SH) generation in imaging the enamel and dentin sections. In addition, microspectroscopy is employed to identify the origin of two-photon fluorescent and SH signals, which are attributed to hydroxyapatite crystals and collagen fibrils, respectively. Hydroxyapatite is found to be present throughout the sections while collagen fibrils only exist in the dentin and dentinoenamel junctions.