Chuanke Wang

Quasi-sinusoidal single-order diffraction transmission grating used in x-ray spectroscopy

A novel design of quasi-sinusoidal single-order diffraction transmission grating (QSTG) is proposed, which can achieve a line density up to thousands line/millimeter as that of traditional transmission gratings with the current level of nanofabrication technique. We fabricate a 1000 line/mm QSTG using the new design approach, and display the calibration results of such QSTG on the soft x-ray beam of synchrotron radiation.

Characterization of the diffraction properties of quantum-dot-array diffraction grating

A new dispersive element named as quantum-dot-array diffraction grating [L. F. Cao, China patent No. 200410081499 (August 10, 2004)] for visible light has been developed and characterized experimentally. A large number of quantum dots distributed on a substrate as sinusoidal function can be used to diffract x rays without higher-order diffraction. The experimental patterns show that the higher-order diffractions which inevitably exist in the spectrum recorded using traditional diffraction gratings can be eliminated effectively by this newly designed element. It indicates that quantum-dot-array diffraction grating could be an attractive alternative of presently used diffraction grating in soft x-ray spectroscopy application to get rid of the higher-order diffraction distortions.

Quantum-dot-array diffraction grating with single order diffraction property for soft x-ray region

A gold transmission grating is used routinely to disperse the x-ray spectrum at the Z soft x-ray facility to measure the spectrum and temporal history of the absolute soft x-ray power emitted from z-pinch and hohlraum radiation sources. A quantum-dot-array diffraction grating (QDADG) of 250 lines/mm for soft x-ray is designed and fabricated for the first time according to the principle of binary sinusoidal transmission grating. The diffraction efficiencies of the grating are measured in the 150-300 eV photon energy range on the Beamline 3W1B of Beijing Synchrotron Radiation Facility. This article describes the basic concept and calibration techniques and presents calibration results. It is shown that the 250 lines/mm QDADG can be used to disperse light without higher-order diffractions in soft x-ray range, and the diffraction efficiencies of this grating are nearly constant (about 25%), which is beneficial in the spectrum analysis.

Low threshold random lasing actions in natural biological membranes

We report random lasing actions stemming from natural biological membranes doped with Rhodamine 6G (Rh6G) laser dye which were then stimulated by a pulsed laser. The membranes have concave–convex structures and are expected to form resonators for weak light scatterings. The laser emission varies with the type of membrane and is also closely related to the dye concentration and pump energy. The threshold for the laser generation obviously rises when the concentration of doped laser dye is increased. The simulation results show lasing distributions are localized, indicating that the laser modes are very sensitive to the indicant angles of pump light.

Random laser action from a natural flexible biomembrane-based device

Abstract Incoherent random lasing action in flexible eggshell membranes infiltrated with rhodamine 6G laser dyes is demonstrated. Laser radiation is achieved by exciting samples with 1-ns pulses at 526 nm. A threshold of 58 μJ/pulse is measured for the samples. The minimum threshold decreases to 35 μJ/pulse after the sample is coated with gold nanoparticles using a magnetron sputtering technique. The peaks of emission spectra are observed to redshift from 576 to 596 nm as dye concentration rises from 0.03 to 0.6 wt%. A linewidth of approximately 5 nm is obtained for most samples. This study is expected to offer a new way to induce lasing emission using biological microfibrils, and enriches basic knowledge of biophotonics.

Single-order diffraction grating designed by trapezoidal transmission function.

Diffraction grating is a widely used dispersion element in spectral analysis from the infrared to the x-ray region. Traditionally, it has a square-wave transmission function, suffering from high-order diffraction contamination. Single-order diffraction can be achieved by sinusoidal amplitude transmission grating, but the fabrication is difficult. Here, we propose a novel idea to design a grating based on trapezoidal transmission function, which makes traditional grating a special case. Grating designed by this idea can not only suppress higher order diffraction by several orders of magnitude as sinusoidal amplitude grating does but also greatly reduce the fabrication difficulty to the level of processing for traditional grating. It offers a new opportunity for fabrication of grating with single-order diffraction and measurement of spectrum without contamination of high-order harmonic components. This idea can easily extend to varied-line-space grating, concave grating with single-order diffraction, or zone plates with single foci and will bring great changes in the field of grating applications.

Phase-type quantum-dot-array diffraction grating

A novel phase-type quantum-dot-array diffraction grating (QDADG) is reported. In contrast to an earlier amplitude-type QDADG [C. Wang et al., Rev. Sci. Instrum. 78, 053503 (2007)], the new phase-type QDADG would remove the zeroth order diffraction at some certain wavelength, as well as suppressing the higher-order diffractions. In this paper, the basic concept, the fabrication, the calibration techniques, and the calibration results are presented. Such a grating can be applied in the research fields of beam splitting, laser probe diagnostics, and so on.

Random laser action from ceramic-doped polymer films

Abstract We report random lasing emission from polymer films doped with ceramic particles in a gain medium. The Al2O3 particles and Rh6G laser dye-doped PVP films were fabricated by a spin-coating technique and they were exposed to a pulsed laser at 526 nm, by which we collected intensive feedback random laser (IFRL) emission when the pump energy reached thresholds. The threshold depended on particle size, film thickness and particle contents in solution. A model with randomly distributed scatterers was established to confirm that the scattering properties could strongly effect the thresholds and lasing spatial distributions.

The realization of long focal depth with a linear varied-area zone plate

Abstract We report a linear varied-area zone plate, in which arbitrary long focal depth can be achieved by properly adjusting the corresponding parameters. Meanwhile, the lateral focal spot and side lobes can be kept very small. Numeral simulations are carried out to verify the performance of our zone plate through Fresnel–Kirchhoff diffraction theory, and the results are in good accord with the experimental verifications. The influences of our zone plate’s parameters to the intensity distribution in focal region are discussed in detail. Comparisons are made with the behaviour of a linear varied-line-space grating, and we find that the behaviour of our novel zone plate along optical axis is just like a reverse transformation of the focusing behaviour of a linear varied-line-space grating.

Characterization of a quasi-sinusoidal transmission grating without membrane substrate in the 200–1500 eV photon energy regions

A 1000-line/mm quasi-sinusoidal transmission grating (QSTG) without membrane substrate has been designed and fabricated, which is utilized to eliminate the higher order diffraction for soft X-ray spectrum measurement in the experiments of inertial confinement fusion. The grating was calibrated using an X-ray beam on synchrotron radiation facility. It shows that the QSTG has the desired diffraction property and the higher order diffraction components are efficiently suppressed in the photon energy ranges from 200 to 1500 eV.