While multiphoton microscopy (MPM) has been performed with a wide range of excitation wavelengths, fluorescence emission has been limited to the visible spectrum. We introduce a paradigm for MPM of near-infrared (NIR) fluorescent molecular probes via nonlinear excitation at 1550 nm. This all-NIR system expands the range of available MPM fluorophores, virtually eliminates background autofluorescence, and allows for use of fiber-based, turnkey ultrafast lasers developed for telecommunications.
We describe multimodal nonlinear microscopy using a compact, turnkey femtosecond fiber laser at 1.5 μm. The system
allows for multiplexed detection of near infrared and visible contrast agents through two-and three-photon excitation
fluorescence microscopy as well as structural imaging viaauto-confocal microscopy (ACM). This platform expands the
available emission spectrum for multiphoton microscopy, enables simultaneous structural and functional imaging, and
offers advantages in penetration depth, contrast, and simplicity as compared to conventional MPM near 800 nm
excitation.
We describe a wide-field preclinical imaging system optimized for time-gated detection of quantum dot fluorescence emission. As compared to continuous wave measurements, image contrast was substantially improved by suppression of short-lifetime background autofluorescence. Real-time (8 frames/s) biological imaging of subcutaneous quantum dot injections is demonstrated simultaneously in multiple living mice.
Novel supercontinuum generation by launching ultra-short femtosecond laser pulses into single crystal sapphire fibers is
demonstrated. Supercontinuum generation using sapphire fiber exhibits many advantages that include high transparency
up to 5 micron, low material dispersion in the 0.8 micron to 5 micron spectral range, and an extremely high laser damage
threshold (500 times higher than that of silica). Thus, supercontinuum spectrum with high power, super broadband, and
spatial coherence can be realized by pumping single crystal sapphire fibers. By experimental comparison, we prove that
sapphire fiber can provide a broader supercontinuum spectrum than that of bulk sapphire counterpart under the same
exciting conditions. Since supercontinuum generation in single crystal sapphire fibers can radiate high power
supercontinuum in the middle-IR regime, it will have a great impact on many applications, including sensing and
broadband multi-spectrum free space communications.
In this paper, we report the fabrication of higher-order-mode rejected fiber Bragg gratings (FBGs) in sapphire crystal fiber using infrared (IR) femtosecond laser illumination. The grating is tested in high temperature furnace up to 1600 degree Celsius. As sapphire fiber is only available as highly multimode fiber, a scheme to filter out higher order modes in favor for the fundamental mode is theoretically evaluated and experimentally demonstrated. The approach is to use an ultra thin sapphire crystal fiber (60 micron in diameter) to decrease the number of modes. The small diameter fiber also enables bending the fiber to certain radius which is carefully chosen to provide low loss for the fundamental mode LP01 and high loss for the other high-order modes. After bending, less-than-2-nm resonant peak bandwidth is achieved. The grating spectrum is improved, and higher resolution sensing measurement can be achieved. This mode filtering method is very easy to implement. Furthermore, the sapphire fiber is sealed with hi-purity alumina ceramic cement inside a flexible high temperature titanium tube, and the highly flexible titanium tube offers a robust packaging to sapphire fiber.
Our high temperature sapphire grating sensor is very promising in extremely high temperature sensing application.
We demonstrate a broad supercontinuum source by bridging two separate supercontinua that are pumped at two different
IR wavelengths. Two separate supercontinua are overlapped to form a broadband supercontinuum source without
spectrum discontinuity between two different pumping sources. The bridging effect of two separate supercontinua is
successfully demonstrated by applying two pumping sources at 1460 nm and 1769 nm into a regular single mode fiber.
Also, more than 1000 nm expansion possibility due to the bridging effect can be achieved by pumping at 1350 nm and
1963 nm.
In this work, the recent work on fabricating harsh environment fiber grating by femtosecond laser and applications as multi-parameter sensor is reported. Bragg gratings have been written in single mode (SM), multimode (MM) silica fiber, polarization maintaining (PM) single mode silica fiber, and highly multimode 60-micron thinned sapphire fiber. Silica gratings can survive in temperatures higher than 1000°C. Sapphire fiber grating can even go as high as 2000°C. Multiple parameter integrated fiber sensor that can detect vector bending and ambient temperature simultaneously with a single asymmetric fiber Bragg grating is realized in MM silica fiber and PM silica fiber. Higher order modes of sapphire Bragg grating is filtered out by mode winding to realize single mode operation.
Dielectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals grown by a modified Bridgman method are investigated under strong, high frequency (>100 kHz) AC field. It is found that there is a phase transition due to the applied AC field, which may be due to the following reasons: (1) strong AC field quickly switches the polarization directions of domains that heats up the crystal due to the friction of domain change; (2) phase transition happens because of the increase of the temperature. Comparing with conventional heating techniques, AC field induced phase transition is a quicker more effective way. Experimental results confirm the increase of d33 and the change of transmittance under strong AC field.
In this paper, a unique non-contact, minimum invasive technique for the assessment of mechanical properties of single cardiac myocyte is presented. The assessment process includes following major steps: (1) attach a micro magnetic bead to the cell to be measured, (2) measure the contractile performance of the cell under the different magnetic field loading, (3) calculate mechanical loading force, and (4) derive the contractile force from the measured contraction data under different magnetic field loading.
In this paper, electro-optic properties of 0.67Pb(Mg1/3Nb2/3)03-0.33PbTiO3 (PMN-33%PT) single crystals under proper AC bias are reported. It is found that PMN-33%PT has an extremely large linear electro-optic coefficient, r33 ~9800 pm/V under proper AC bias. Besides this huge electro-optic coefficient, PMN-33%PT crystals also have very good optical quality and the random scatterings caused by the multiple domains can be totally removed by the AC bias. Furthermore, unlike KTN, PMN-PT has a much higher phase transition temperature (~175°C), which is sufficiently away from the room temperature so that a good thermal stability can be achieved. The combinations of giant electro-optic coefficient, good optical quality, and high thermal stability may make PMN-33%PT the best electro-optic material among all electro-optic crystals developed so far, which could revolutionize applications of electro-optic crystals to telecommunications, medical imaging, et al. This research may also help to understand the mechanism underlying the ultrahigh performance of this new generation of single crystal materials (e.g., PZN-PT, PMN-PT) via the interaction between crystal internal structures and external AC electric field, which may stimulate further interest in the fundamental theory of ferroelectrices under changing electric field that could direct improving the quality of existing ferroelectric crystals and developing new ferroelectric crystals.
In this paper, some recent advances in long period gratings, including (1) widely tunable single resonant band long period gratings, (2) long period gratings fabricated in single crystal sapphire fibers, and (3) long period gratings fabricated in photonic crystal fibers are presented. The applications of these novel long period grating to next generation ultra high capacity optics communication networks, high temperature distributed fiber optic sensors, and highly sensitive biosensors are discussed. Quantitative analyses and preliminary experimental results are provided.
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