Jyhpyng Wang

Noninterferometric differential confocal microscopy with 2-nm depth resolution

Abstract By utilizing the sharp slopes of the axial response curve of confocal imaging, we demonstrate a differential confocal technique for surface imaging with depth resolution as great as 2 nm. Neither servo feedback loop nor lock-in detection are used, hence measurements can be performed at high speed with long working distance. Because the technique uses no interferometric effects, it offers large open-loop dynamic range and is compatible with fluorescence microscopy.

Fabrication of spatial transient-density structures as high-field plasma photonic devices

Fabrication of periodic transient-density structures in a gas jet with a boundary scale length approaching 10μm was demonstrated. This was achieved by passing an ultrashort high-intensity laser pulse through a patterned mask and imaging the mask onto the target plane. Gas/plasma density at the laser-irradiated regions drops as a result of hydrodynamic expansion following ionization and heating by the laser pulse. The fabrication of gas/plasma density structures with such a scheme is an essential step in the development of plasma photonic devices for applications in high-field physics.

Self-starting issues of passive self-focusing mode locking.

An analysis of passive mode locking with the intracavity self-focusing effect is presented, and the self-starting issue is addressed. The analysis shows that the initial pulse-shortening force of this mechanism is too weak to start the mode locking from mode beating or noise and how it can be greatly enhanced with a dilute dye saturable absorber in the cavity. This analysis also shows shortening force in cw mode-locking lasers.

Efficient generation of extended plasma waveguides with the axicon ignitor-heater scheme

By using an axicon lens in conjunction with the ignitor-heater scheme, a 1.2-cm-long high-quality plasma waveguide is generated efficiently, which can extend the range of laser-plasma interaction much beyond the limit of Rayleigh range

Programmable fabrication of spatial structures in a gas jet by laser machining with a spatial light modulator

Programmable fabrication of longitudinal spatial structures in a gas jet was achieved by using laser machining with a liquid-crystal spatial light modulator as the pattern mask. By this technique single-shot fabrication of arbitrary gas and/or plasma structures is demonstrated, which establishes the crucial step toward raising the designs and applications of high-field plasma devices to the level of adaptive feedback optimization.

Optical measurement of the viscoelastic and biochemical responses of living cells to mechanical perturbation

We have developed an optical method for real-time monitoring of cellular motion in a natural environment with nanometer resolution. From the motion driven by small optical forces, we measured dynamic viscoelastic responses of living cells in the linear reversible region. Cytoplasmic gel-to-sol transition that was due to the disruption of the actin-filament framework was detected, and a linear release of Ca(2+) from intracellular storage that was related to submicrometer cell deformation was observed. The method was shown to be a powerful tool for studying the natural response of cells to mechanical perturbation.

Spatially coherent white-light interferometer based on a point fluorescent source

We developed a point-fluorescent-source-based white-light interferometer for high-resolution reflectometry, range-gating imaging, and group-velocity-dispersion measurement. The laser-pumped point fluorescent source has 9 mW of power and a spatial coherence of 0.97, which allows it to be used like a laser beam. Owing to its 40-nm FWHM spectral width, the width of its temporal autocorrelation is only 19 fs, which corresponds to that of 14-fs Gaussian pulses.

Tomography of high harmonic generation in a cluster jet.

Tomography of high harmonic generation in a cluster jet was achieved by using laser machining. The growth curves help explain the optimal backing pressure, which is ascribed to the change in phase matching condition.

Deconvolution of local surface response from topography in nanometer profilometry with a dual-scan method

In profilometric measurements, by scanning the sample twice with a fixed vertical offset, one can separate the signal that comes from surface heterogeneity from the topographic signal. Using differential confocal microscopy, a newly developed open-loop nanometer profilometric technique, we demonstrated this dual-scan method on composite samples and obtained 10-nm depth resolution. This technique can also be applied to other profilometric techniques such as atomic force microscopy and scanning tunneling microscopy.

Imaging and profiling surface microstructures with noninterferometric confocal laser feedback

Exploiting the sensitivity and the self‐aligning features of the confocal laser‐feedback technique and the convenience of superluminescent laser diodes, we developed an optical method for imaging and profiling surface microstructures with a depth resolution as great as 20 nm. The incoherent, noninterferometric nature of the technique enables fast open‐loop operation and large dynamic range. Measurements of calibrated semiconductor surface microstructures and optical ridge waveguides are demonstrated.