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In the current study, a multi-wavelength light-emitting diode (LED)-integrated CMOS imaging device was developed to investigate the effect of various wavelengths on multiple color characterization. Various color pigments (black, red, green, and blue) were applied on both white paper and skin phantom surfaces for quantitative analysis. The artificial skin phantoms were made of polydimethylsiloxane (PDMS) mixed with coffee and TiO2 powder to emulate the optical properties of the human dermis. The customized LED-integrated imaging device acquired images of the applied pigments by sequentially irradiating with the LED lights in the order of white, red, green, and blue. Each color pigment induced a lower contrast during illumination by the light with the equivalent color. However, the illumination by light with the complementary (opposite) color increased the signal-to-noise ratio by up to 11-fold due to the formation of a strong contrast (i.e., red LED = 1.6 ± 0.3 vs. green LED = 19.0 ± 0.6 for red pigment). Detection of color pigments in conjunction with multi-wavelength LEDs can be a simple and reliable technique to estimate variations in the color pigments quantitatively.

The feasible application of double-layered skin phantoms was evaluated to identify artificial blood flow with a Doppler optical coherence tomography (DOCT) system for laser tattoo treatments. Polydimethylsiloxane (PDMS) was used to fabricate the artificial phantoms with flow channels embedded. A double-integrating sphere system with an inverse adding-doubling method quantified both the absorption and the reduced scattering coefficients for epidermis and dermis phantoms. Both OCT and caliper measurements confirmed the double-layered phantom structure (epidermis = 136 ± 17 µm vs. dermis = 3.0 ± 0.1 mm). The DOCT method demonstrated that high flow rates were associated with high image contrast, visualizing the position and the shape of the flow channel. Application of the channel-embedded skin phantoms in conjunction with DOCT can be a reliable technique to assess dynamic variations in the blood flow during and after laser tattoo treatments.

We designed and fabricated a telecentric f-theta imaging lens (TFL) to improve the imaging performance of spectral domain optical coherence tomography (SD-OCT). By tailoring the field curvature aberration of the TFL, the flattened focal surface was well matched to the detector plane. Simulation results showed that the spot in the focal plane fitted well within a single pixel and the modulation transfer function at high spatial frequencies showed higher values compared with those of an achromatic doublet imaging lens, which are commonly used in SD-OCT spectrometers. The spectrometer using the TFL had an axial resolution of 7.8 μm, which was similar to the theoretical value of 6.2 μm. The spectrometer was constructed so that the achromatic doublet lens was replaced by the TFL. As a result, the SD-OCT imaging depth was improved by 13% (1.85 mm) on a 10 dB basis in the roll-off curve and showed better sensitivity at the same depth. The SD-OCT images of a multi-layered tape and a human palm proved that the TFL was able to achieve deeper imaging depth and better contrast. This feature was seen very clearly in the depth profile of the image. SD-OCT imaging performance can be improved simply by changing the spectrometer’s imaging lens. By optimizing the imaging lens, deeper SD-OCT imaging can be achieved with improved sensitivity.

We experimentally demonstrate a passively mode-locked thulium doped fiber laser using a bismuth telluride deposited multimode interference (MMI) fiber at a wavelength of 1958 nm. Our MMI based saturable absorber was fabricated by fusion splicing with single mode fiber and null core fiber. The center wavelength and insertion loss of MMI fiber were measured to be ~ 1958 nm and 3.4 dB. We observed a passively mode locked thulium doped fiber laser operating at a wavelength of 1958 nm. The temporal pulse width of output pulses is 4.2 ps with repetition rate of 22.7 MHz.

We proposed complex conjugate-free optical coherence tomography imaging method and demonstrated its performance on mirror image suppression operating in fiber-based interferometer. Artifact image given by twin peaks after the Fourier transform of real interferogram could be removed by using the Doppler shift induced by vibrations, which is utilized for the retrieval of complex signal. To induce the Doppler shift, in the experiment, piezoelectric transducer(PZT) was attached on coiled fiber in reference arm. With adjusting vibration conditions of the PZT, quantity of the phase shift obtained by the Doppler shift could be controlled in the fiber-based interferometer. With changing vibration frequencies, the performance of mirror image suppression was observed. Although small frequency changes of 15 Hz were adjusted, the complex conjugate-free results could be achieved easily. Because the proposed method could be easily adapted to the fiber-based interferometer, required phase control in fiber-based phase shifted interferometer or interferometer-based imaging system would be performed properly by simple implementation of vibration module.

Most of the two-photon fluorescence microscopes are based on femtosecond Ti:Sapphire laser sources near the 800 nm wavelength. Here, we introduce a new confocal two-photon microscope system using a mode-locked Yb3+-doped fiber laser. The mode-locked fiber laser produces 13 ps pulses with large positive chirping at a repetition rate of 36 MHz with an average power of 80 mW. By using an external grating pair pulse compressor, the pulse width and the frequency chirping of the laser output are controlled for optimum two-photon excitation. For a given objective lens, the optimum condition was obtained by monitoring the two-photon-induced-photocurrent in a GaAsP photodiode at the sample position. The performance of this pulse width optimized two-photon microscope system was demonstrated by imaging Vybrant DiI-stained dorsal root ganglion cells in 2 and 3 dimensions. (C) 2012 Optical Society of America

Two-photon microscopy is a very attractive tool for the study of the three-dimensional (3D) and dynamic processes in cells and tissues. One of the feasible constructions of two-photon microscopy is the combination a confocal laser scanning microscope and a mode-locked Ti:sapphire laser. Even though this approach is the simplest and fastest implementation, this system is highly cost-intensive and considerably difficult in modification. Many researcher therefore decide to build a more cost-effective and flexible system with a self-developed software for operation and data acquisition. We present a custom-built two-photon microscope based on a mode-locked Yb3+ doped fiber laser and demonstrate two-photon fluorescence imaging of biological specimens. The mode-locked fiber laser at 1060 nm delivers 320 fs laser pulses at a frequency of 36 MHz up to average power of 80 mW. The excitation at 1060 nm can be more suitable in thick, turbid samples for 3D image construction as well as cell viability. The system can simply accomplish confocal and two-photon mode by an additional optical coupler that allows conventional laser source to transfer to the scanning head. The normal frame rate is 1 frames/s for 400 x 400 pixel images. The measured full width at half maximum resolutions were about 0.44 μm laterally and 1.34 μm axially. A multi-color stained convallaria, rat basophilic leukemia cells and a rat brain tissue were observed by two-photon fluorescence imaging in our system.

Multi point fluorescence measurement system using basic image shifting method and commercial multi mode fiber is presented in this paper. Using a singlet lens, the original fluorescence image of a sample is shifted to another plane which can be monitored using ccd, and at the first image plane independent two fiber tips in an xyz stage deliver each fluorescent signal at a specific sample position to a fluorescence correlation spectroscopy (FCS) with an electron multiplying charge coupled device (EMCCD). The FCS is composed with an EMCCD, which can detect single molecule level fluorescence light. Applying region of interest (ROI) and pixel binning, a time resolution of up to 2 ms can be achieved, which is sufficient to resolve the diffusion of fluorescence micro-sphere in solution. The advantages of implementing EMCCD cameras in wide-field ultra low light imaging, as well as in site-specific multi-point fluorescence measurement system, can consequently also be exploited for spatially and spectrally resolved FCS. Experimental results about FCS with spectrum informations demonstrate the advantage of the simplicity and flexibility of our system. We expect that this multi point measurement system also can be applied to other study of bio molecular dynamics.

We constructed a passively mode-locked Er-doped fiber laser (PML-EDFL). It generates ~ 1.3 ps pulses at a repetition rate of 12 MHz with an average output power of 0.7 mW. These pulses are amplified in a short Er-doped fiber amplifier (EDFA) which is composed of low nonlinearity EDF. The average power of amplified pulse is about 15 mW. And its pulse width is about 880 fs. An all-fiber supercontinuum (SC) is generated by putting the amplified fiber laser pulse at the wavelength of 1. 56 mm into the highly nonlinear dispersion shifted fiber (HN-DSF) whose zero dispersion wavelength is 1.537 mm and nonlinear coefficient is about 10.5/W/km at the input wavelength. The polarization state of the generated SC spectra is well defined such that it can be properly controlled by the polarization controller. By using a delayed pulsed method, we report an experimental study of the coherence of SC spectra generated through a HN-DSF. In this paper, the strong dependence of the spectral coherence on the HN-DSF length is observed experimentally. And optimal conditions for obtaining wide SC with high coherence are investigated in detail. We believed that our proposed all-fiber laser based SC source with high coherence has many important applications in recently developed frequencydomain measurement techniques such as optical coherence tomography (OCT), optical frequency domain imaging (OFDI), optical frequency domain reflectometry (OFDR) and their instrumentation.

Achieving a greater imaging depth with two-photon fluorescence microscopy (TPFM) is mainly limited by out-of-focus fluorescence generated from both ballistic and scattered light excitation. We report on an improved signal-to-noise ratio (SNR) in a highly scattering medium as demonstrated by analytical simulation and experiments for TPFM. Our technique is based on out-of-focus rejection using a confocal pinhole. We improved the SNR by introducing the pinhole in the collection beam path. Using the radiative transfer theory and the ray-optics approach, we analyzed the effects of different sizes of pinholes on the generation of the fluorescent signal in the TPFM system. The analytical simulation was evaluated by comparing its results with the experimental results in a scattering medium. In a combined confocal pinhole and two-photon microscopy system, the imaging depth limit of approximately 5 scattering mean free paths (MFP) was found to have improved to 6.2 MFP. (C) 2012 Optical Society of America

We present the development and implementation of a spatially and spectrally resolved multipoint fluorescence correlation spectroscopy (FCS) system utilizing multiple end-capped optical fibers and an inexpensive laser source. Specially prepared end-capped optical fibers placed in an image plane were used to both collect fluorescence signals from the sample and to deliver signals to the detectors. The placement of independently selected optical fibers on the image plane was done by monitoring the end-capped fiber tips at the focus using a CCD, and fluorescence from specific positions of a sample were collected by an end-capped fiber, which could accurately represent light intensities or spectral data without incurring any disturbance. A fast multipoint spectroscopy system with a time resolution of ∼1.5 ms was then implemented using a prism and an electron multiplying charge coupled device with a pixel binning for the region of interest. The accuracy of our proposed system was subsequently confirmed by experimental results, based on an FCS analysis of microspheres in distilled water. We expect that the proposed multipoint site-specific fluorescence measurement system can be used as an inexpensive fluorescence measurement tool to study many intracellular and molecular dynamics in cell biology.