[Show abstract][Hide abstract] ABSTRACT: A donut-shaped laser that is simultaneously impacted by the coma, astigmatism and spherical aberrations in a high NA focusing system is numerically simulated based on the vectorial diffraction theory. The full-width half-maximum, intensity characters, and dimensions of the dark cores of the donut-shaped laser on the focal plane are quantitatively analyzed. The results are highly consistent with the annular-shaped nano-patterns that are experimentally fabricated by our purpose-built laser direct writing system. The mechanism of asymmetric nano-patterns fabricated through laser writing lithography is also revealed.
Full-text · Article · Dec 2014 · Journal of optics
[Show abstract][Hide abstract] ABSTRACT: The surface effect is becoming apparently significant as the miniaturization of fluidic devices. In the micro/nanochannel fluidics, the electrode surface effects have the same important influence on the current signals as the channel surface effects. In this paper, when aqueous solution are driven with non-continuous DC electric field force, the characteristics of current signals of the fluid transferring through microfluidic channel are systematically studied. Six modes of current signal are summarized, and some new significant phenomena are found, e. g. there exists a critical voltage at which the steady current value equals to zero; the absolute value of the steady current decreases at first, however, it increases with the external voltage greater than the critical voltage as the electrode area ratio of cathode and anode is 10 and 20; the critical voltage increases with the enhancing of electrode area ratio of cathode and anode and solution pH, while it decreases with the raising of ion concentration. Finally, the microscopic mechanism of the electrode surface charge effects is discussed preliminarily. The rules will be helpful for detecting and manipulating single biomolecules in the micro/nanofluidic chips and biosensors. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
[Show abstract][Hide abstract] ABSTRACT: We report a passively continuous wave (CW) mode-locked femtosecond 1.908 mu m Tm:LiYF4 (Tm:YLF) slab laser based on an output-coupling graphene saturable absorber mirror (GSAM) with a transmittance of 2.29%. Using an atmospheric-pressure chemical vapor deposition (APCVD) method with a C2H2 carbon source, triple-layer graphene was fabricated and transferred to an output-coupling mirror of 1.9 mu m wavelength range. Stable CW mode-locked laser pulses as short as 473 fs were measured with a repetition rate of 70.2 MHz and an average output power of 146.5 mW at 1.908 mu m. (C) 2013 The Japan Society of Applied Physics
No preview · Article · Oct 2013 · Applied Physics Express
[Show abstract][Hide abstract] ABSTRACT: A Laser diode (LD) side-pumped ceramic Nd:YAG laser was developed to
achieve dual wavelength output at 532nm and 660nm, based on
LiB3O5 (LBO) intracavity frequency doubling with
the method of β-BaB2O4 (BBO) electro-optical
Q-switching (EO Q-switching). In the experiment, a T-shaped cavity is
designed for laser oscillate to reach the maximum output power of 8.32W
at 532nm and 4.2W at 660nm simultaneously; and also, the pulse widths
could reach to 88.6ns at 532nm and 96ns at 660nm with the repetition
rate of 10kHz. The beam quality factors (M2) could be
measured as Mx2=4.36, My2=4.78 at 532nm and Mx2=5.46, My2=5.83 at 660nm.
Both the power instabilities of the two output wavelengths are less than
2% in 10h measured at every 1h. All of the EO Q-switching technique,
oscillation cavity design and laser gain media, used in this work,
illustrate a valid way to develop a dual-wavelength laser with high
output peak power.
[Show abstract][Hide abstract] ABSTRACT: Nanoscale functional structures are indispensable elements in many fields of modern science. In this paper, nanopillar array with a pillar diameter far smaller than Abbe's diffraction limit is realized by a new kind of continuous wave (CW) laser direct lithography technology. With atomic force microscopy technology, the average diameter of nanopillars on thin OIR906 photoresist film is about 65 nm and the smallest diameter is 48 nm, which is about 1/11 of the incident laser wavelength. Also, the influences of coma and astigmatism effects to the shape and size of nanopillar are numerically simulated by utilizing vector integral. As far as we know, it is the first time that nanopillar array is implemented by a donut-shaped 532-nm visible CW laser. The study presents a new, simple, inexpensive, and effective approach for nanopillar/pore array fabrication.
Full-text · Article · Jun 2013 · Nanoscale Research Letters
[Show abstract][Hide abstract] ABSTRACT: This paper experimented with the λ-DNA molecules which were successfully stretched on the hydrophobic surface of PMMA by the molecular combing method in a wide concentration range from 7mM to 20mM of tris buffer. The buffer concentration has a remarkable influence on the properties of the stretched DNA such as the length and uniformity. The results demonstrated the most applicable concentration of tris buffer for λ-DNA stretching is 10mM.
[Show abstract][Hide abstract] ABSTRACT: Fluorescence emission from in vivo cutaneous melanin was recently detected under near-infrared (NIR) excitation by our group. We then built a prototype NIR autofluorescence imaging system to observe and characterize the melanin distribution in human skin. In this article, we reported a new setup of NIR fluorescence imaging system and calibration methods to optimize the system for better clinical feasibility and clearer image.
The imaging system was designed to perform both fluorescence and reflectance imaging with a 785-nm fiber-coupled laser source. The illumination light was purified by a 785-nm bandpass filter for fluorescence excitation; while the spontaneous components were selected by a longpass filter for NIR reflectance imaging. A hand-controlled filter wheel was used to switch these two filters for different imaging modes. A dichroic filter was used to guide the illuminating light onto the skin surface for excitation. Reflectance and fluorescence signals were collected sequentially by a NIR optimized CCD camera. The captured images were calibrated by the reflectance images of a standard reflectance disk for non-uniform illuminations and light collection efficiencies.
The clinical results demonstrated that NIR fluorescence intensities and distribution patterns vary among lesion types. It was also confirmed that pigmented skin lesions emitted higher NIR fluorescence than the surrounding normal skin due to the presentation of higher concentrations of cutaneous melanin within the lesions.
NIR autofluorescence imaging system could be utilized as a powerful tool for visualizing melanin distribution in pigmented skin lesions and as a potential method for aiding melanoma detection.
No preview · Article · Jun 2012 · Skin Research and Technology
[Show abstract][Hide abstract] ABSTRACT: In dermatology applications, diffuse reflectance spectroscopy has been
extensively investigated as a promising tool for the noninvasive method
to distinguish melanoma from benign pigmented skin lesion (nevus), which
is concentrated with the skin chromophores like melanin and hemoglobin.
We carried out a theoretical study to examine melanin distribution in
human skin tissue and establish a practical optical model for further
pigmented skin investigation. The theoretical simulation was using
junctional nevus as an example. A multiple layer skin optical model was
developed on established anatomy structures of skin, the published
optical parameters of different skin layers, blood and melanin. Monte
Carlo simulation was used to model the interaction between excitation
light and skin tissue and rebuild the diffuse reflectance process from
skin tissue. A testified methodology was adopted to determine melanin
contents in human skin based on in vivo diffuse reflectance spectra. The
rebuild diffuse reflectance spectra were investigated by adding melanin
into different layers of the theoretical model. One of in vivo
reflectance spectra from Junctional nevi and their surrounding normal
skin was studied by compare the ratio between nevus and normal skin
tissue in both the experimental and simulated diffuse reflectance
spectra. The simulation result showed a good agreement with our clinical
measurements, which indicated that our research method, including the
spectral ratio method, skin optical model and modifying the melanin
content in the model, could be applied in further theoretical simulation
of pigmented skin lesions.
No preview · Article · Nov 2011 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: The autofluorescence properties of normal human skin in the near-infrared (NIR) spectral range were studied using Monte Carlo simulation. The light-tissue interactions including scattering, absorption and anisotropy propagation of the regenerated autofluorescence photons in the skin tissue were taken into account in the theoretical modeling. Skin was represented as a turbid seven-layered medium. To facilitate the simulation, ex vivo NIR autofluorescence spectra and images from different skin layers were measured from frozen skin vertical sections to define the intrinsic fluorescence properties. Monte Carlo simulation was then used to study how the intrinsic fluorescence spectra were distorted by the tissue reabsorption and scattering during in vivo measurements. We found that the reconstructed model skin spectra were in good agreement with the measured in vivo skin spectra from the same anatomical site as the ex vivo tissue sections, demonstrating the usefulness of this modeling. We also found that difference exists over the melanin fluorescent wavelength range (880-910 nm) between the simulated spectrum and the measured in vivo skin spectrum from a different anatomical site. This difference suggests that melanin contents may affect in vivo skin autofluorescence properties, which deserves further investigation.
No preview · Article · Sep 2011 · Journal of photochemistry and photobiology. B, Biology
[Show abstract][Hide abstract] ABSTRACT: Raman spectroscopy has been used as a sensitive tool for studying biological tissue and evaluating disease. In many applications, microscopic level resolution spectral analysis is desirable. And this has been performed mostly by expensive commercial confocal micro-Raman systems. In this research, we present a simple method for building an economical and modular Raman microspectroscopy system that combines a microscope with a Raman spectrometer using an optical fiber bundle. The bundle with a circular collection end is positioned at an image plane of the microscope to collect Raman signals from the interested micro-location on the sample. The light delivery end is specially configured so that its 37 fibers are arranged along a straight line to fit into the spectrometer entrance slit. This configuration improves light collection efficiency and maintains high spectral resolution. To battle the great background autofluorescence and Raman signals that could originate from the microscope slides and optics due to the non-confocal set-up of our simplified system, conventional normal-incident illumination is replaced by oblique illumination at 45° degrees and the microscope slides are coated with gold. We demonstrated the usefulness of the system by measuring micro-Raman spectra from different skin layers on vertical sections of normal skin tissue samples.