Ultrawideband photonic crystal fiber coupler for multiband optical imaging system.

We report a photonic crystal fiber (PCF) coupler having an ultrawide spectral bandwidth keeping single mode operation. The use of the PCF coupler in a fiber-based optical coherence tomography (OCT) system enables us to handle the wide spectral bands of various light sources, including superluminescent diodes (SLDs) at 1300 nm and 820 nm, Ti:sapphire lasers, and white-light sources. The multiband imaging performances of the PCF-based OCT system are demonstrated by obtaining dental images at 1300 nm and 820 nm with the same setup.

Rotational multiphoton endoscopy with a 1 microm fiber laser system.

We present multiphoton microendoscopy with a rotational probe and a 1 microm fiber-based femtosecond laser. The rotational probe is based on a double-clad photonic crystal fiber, a gradient index lens, a microprism, and a rotational microelectronicmechanical system (MEMS) motor. The MEMS motor has a diameter of 2.

Photochemistry and electron-transfer mechanism of transition metal oxalato complexes excited in the charge transfer band.

The photoredox reaction of trisoxalato cobaltate (III) has been studied by means of ultrafast extended x-ray absorption fine structure and optical transient spectroscopy after excitation in the charge-transfer band with 267-nm femtosecond pulses. The Co-O transient bond length changes and the optical spectra and kinetics have been measured and compared with those of ferrioxalate. Data presented here strongly suggest that both of these metal oxalato complexes operate under similar photoredox reaction mechanisms where the primary reaction involves the dissociation of a metal-oxygen bond.

Miniaturized probe based on a microelectromechanical system mirror for multiphoton microscopy.

A factor that limits the use of multiphoton microscopy (MPM) in clinical and preclinical studies is the lack of a compact and flexible probe. We report on a miniaturized MPM probe employing a microelectromechanical system (MEMS) scanning mirror and a double-clad photonic crystal fiber (DCPCF). The use of a MEMS mirror and a DCPCF provides many advantages, such as size reduction, rapid and precise scanning, efficient delivery of short pulses, and high collection efficiency of fluorescent signals.

Electron transfer mechanism and photochemistry of ferrioxalate induced by excitation in the charge transfer band.

The photoredox reaction of ferrioxalate after 266/267 nm excitation in the charge transfer band has been studied by means of ultrafast extended X-ray absorption fine structure (EXAFS) analysis, optical transient spectroscopy, and quantum chemistry calculations. The Fe-O bond length changes combined with the transient spectra and kinetics have been measured and in combination with ultrahigh frequency density functional theory (UHF/DFT) calculations are used to determine the photochemical mechanism for the Fe(III) to Fe(II) redox reaction. The present data and the results obtained with 266/267 nm excitations strongly suggest that the primary reaction is the dissociation of the Fe-O bond before intramolecular electron transfer occurs.

Photoelectron detachment and solvated electron dynamics of the cobalt(III) and iron(III) oxalato complexes.

The photochemical redox reaction kinetics of [M(III)(C(2)O(4))(3)](3-) [M = Co, Fe] complexes have been reexamined and studied by time-resolved spectroscopy. The redox mechanisms of the two systems, Co and Fe, were found to be similar to each other, and solvated electrons were observed immediately after 266/267 nm photoexcitation. A reaction mechanism is proposed that involves photoelectron detachment as a primary process.

Transient structures and kinetics of the ferrioxalate redox reaction studied by time-resolved EXAFS, optical spectroscopy, and DFT.

The photoredox reaction transients of ferrioxalate in water have been studied by means of time-resolved EXAFS and ultrafast optical transient spectroscopy. The transient spectra and kinetics have been measured from the femtosecond to millisecond range, and the Fe-O bond lengths of the ferrioxalate redox reaction transients have been determined with 2 ps time resolution and 0.04 A accuracy.

High-resolution frequency-domain second-harmonic optical coherence tomography.

We used continuum generated in an 8.5 cm long fiber by a femtosecond Yb fiber laser to improve threefold the axial resolution of frequency domain second-harmonic optical coherence tomography (SH-OCT) to 12 microm. The acquisition time was shortened by more than 2 orders of magnitude compared to the time-domain SH-OCT.

Second harmonic optical coherence tomography.

Second harmonic optical coherence tomography, which uses coherence gating of second-order nonlinear optical response of biological tissues for imaging, is described and demonstrated.

Low-noise broadband light generation from optical fibers for use in high-resolution optical coherence tomography.

Broadband light generation from a single-mode optical fiber was developed for high-resolution optical coherence tomography (OCT). No noise amplification was observed for light broadened by self-phase modulation. The investigation showed that the intensity noise of light broadened by self-phase modulation in a single-mode optical fiber was much lower than that of continuum light from a microstructure fiber (MSF).

Second-harmonic optical coherence tomography.

Second-harmonic optical coherence tomography, which uses coherence gating of second-order nonlinear optical responses of biological tissues for imaging, is described and demonstrated. Femtosecond laser pulses were used to excite second-harmonic waves from collagen harvested from rat tail tendon and a reference non-linear crystal. Second-harmonic interference fringe signals were detected and used for image construction.

Ultrafast time-resolved transient structures of solids and liquids by means of extended X-ray absorption fine structure.

Detection of ultrafast transient structures and the evolution of ultrafast structural intermediates during the course of reactions has been a long standing goal of chemists and biologists. This article will be restricted to nanosecond, picosecond and shorter time-resolved extended X-ray absorption fine structure (EXAFS) studies, its aim being to present the progress and problems encounter in measurements and understanding the structure of transients. The recent advances in source technology has stimulated a wide variety of novel experiments using both synchrotrons and smaller laboratory size systems.

Measurement of modal dispersion in optical fiber by means of acousto-optic coupling.

We show that frequency-wavelength tuning characteristics of acousto-optic coupling can be used for measuring the difference of effective index, group index, and chromatic dispersion between core and cladding modes in single-mode fibers. Chromatic dispersion measurements of a 30-cm-long conventional single-mode fiber, a nonzero dispersion-shifted fiber, and a dispersion-compensating fiber with this new method are presented for the wavelength range 1500-1600 nm. Qualitative agreement with independently measured data is obtained.

Structures of bromoalkanes' photodissociation in solution by means of ultrafast extended x-ray absorption fine-structure spectroscopy.

The structures of initial and final products of bromoalkanes' photodisociation reaction in cyclohexane solution have been measured with a bond length accuracy of 0.02 A by means of ultrafast time-resolved extended x-ray absorption fine structure spectroscopy. The photoredaction mechanism is also discussed.

Picosecond X-Ray Pulses Generated in a Diode Driven by 193-nm Picosecond Laser Pulses.

A new technique for the generation of picosecond x-ray pulses is presented. Picosecond laser pulses are used to generate ultrashort electron pulses in a conventional x-ray diode in which the cathode is replaced by a photocathode. In the experiments presented, 9-ps UV pulses are employed to produce characteristic x-ray pulses with duration in range of 20-90 ps at a repetition rate of 300 Hz.

Third-harmonic generation in barium borate.

The cubic nonlinear susceptibility of barium metaborate was employed for the generation of phase-matched third-harmonic generation (THG) of 1.053-microm pump radiation. The various processes that are responsible for THG in this crystal are discussed and experimental results for types I and II phase matching are presented.

[The prevention of postoperative suppurative complications in stomach cancer].

Bacteriologic studies of gastric juice and purulent drainage fluids in the event of complications were carried out in 80 patients who had undergone gastric resections and had been on conventional parenteral antibiotic treatment (control group). Another (experimental) group of 37 patient, having undergone the same operations, received prophylaxis of the suppurative complications with 5-nitrox and Flagyl solutions through nasogastric probe once in 3 hours for 6 to 8 days. The suppurative complications in the experimental group were reduced from 47.

[Determination of the transaortic valve gradient in aortic stenosis by continuous Doppler echocardiography].

A correlative study was carried out between the transvalvular aortic gradient determined by continuous wave Doppler echocardiography and by cardiac catheterization (retrograde or transseptal) in 41 patients with proved by invasive methods aortic valvular stenosis of different degree with or without accompanying aortic incompetence (light, moderate or severe). A considerable correlation was found between the transvalvular aortic gradient determined by the two methods (r = 0.75).

[The potentials of pulse Doppler echocardiography for the diagnosis and determination of the degree of mitral stenosis].

84 persons were examined: 61 patients with rheumatic mitral valve stenosis (21 men and 40 women), mean age 39.38 +/- 11.2 years and 23 healthy controls (14 men and 9 women), mean age 25.

[Correlation of functional indices of the left ventricle with structural changes in the myocardium].

11 with dilatative cardiomyopathy, 9 with valvular disease and 3 with ischemic heart disease--a full intracardial examination including right ventricular endomyocardial biopsy was performed. The most severe disorders of the hemodynamic parameters were found in the group of patients with dilatative cardiomyopathy. The pressure in the pulmonary artery was the highest of all groups of patients.

[Indications for and the postoperative results of mitral valve prosthesis].

The influence of 20 hemodynamic and clinical indices on the postoperative results was studied in 528 patients with mitral valve prosthetics. One year after the operation 78.7% of the patients are with improved functional capacity, 18.