Narrow linewidth 2 μm optical parametric oscillation in periodically poled LiNbO<Subscript>3</Subscript> with volume Bragg grating outcoupler

An optical parametric oscillator using a periodically poled LiNbO₃ crystal and a volume Bragg grating output coupler is presented. Signal and idler wavelengths of 2008 and 2264 nm were generated from the 1064 nm Nd:YVO₄ pump laser. The Bragg grating was reflecting in a narrow band around 2008 nm, creating a purely singly resonant cavity. Signal and idler linewidths of approximately 0.44 and 0.72 nm, respectively, were measured. This is a reduction of 80 and 60 times compared to when using a mirror as output coupler. A total output energy of 156 μJ was measured with 47% slope efficiency. PACS 42.65.Yj; 42.72.Ai; 42.40.Eq     

A high-resolution FT-IR study of the fundamental bands nu7, nu8, and nu18 of ethene secondary ozonide

Ozonization reaction of ethene in neat film at 77 K was performed. Separation of ethene secondary ozonide from the other products of the reaction was performed by continuous pumping of the reactor. Only the products, which evaporated from the walls of the reactor at 185 K, were transferred to the gas cell. The high-resolution infrared absorption spectrum of gaseous ethene secondary ozonide (C(2)H(4)O(3)) in a static gas long-path absorption cell has been recorded in the 900-1100 cm(-1) spectral region at 185 K. The spectral resolution was 0.003 cm(-1). Analyses of the nu(7)(A) band at 1037.0 cm(-1), the nu(8)(A) band at 956.1 cm(-1), and the nu(18)(B) band at 1082.1 cm(-1) have been performed using the Watson Hamiltonian model (A, reduction; III(r), representation). A set of ground-state rotational and quartic centrifugal distortion constants have been obtained, and upper state spectroscopic constants have been determined for the bands investigated. A local resonance observed in nu(18) is explained as c-Coriolis interaction with nu(10) + nu(11).     

Bioelectrochemical application of some PQQ-dependent enzymes.

This paper focuses on the use of PQQ-dependent enzymes (PQQ enzymes) in amperometrical biosensors and gives emphasis on their innovative designs and applications. The study covers some aspects in the evolution of biosensors based on PQQ enzymes. Main attention is focused on the electrochemical properties of PQQ enzymes as very promising materials for the formation of electrochemical biosensors. Immobilization approaches and redox mediators recently used in PQQ enzymes based biosensors are reviewed. The acceptance of polypyrrole as a very promising immobilization matrix for some PQQ enzymes is discussed.     

Conformational studies of aliphatic secondary ozonides (propene, 1-butene and 1-heptene) by means of FTIR spectroscopy

Ozonization reaction of simple alkenes was studied by means of FT infrared absorption gas spectroscopy. The reaction was performed at 95 K in neat films of the reactants. IR absorption spectra of the gaseous products were recorded. The spectra were analyzed combining experimental results with theoretical calculations performed at B3LYP 6-311++G (3df, 3pd) level. We found that among all theoretically predicted conformers of propene secondary ozonide, only one which has the O-O half-chair configuration for the five membered ring and the radical attached in the equatorial position was present in the sample. Samples of 1-butene and 1-heptene secondary ozonides consist from two conformers of very similar energy (ΔH=0.3 kJ/mol). The most stable conformer for both ozonides is the one with O-O half-chair configuration of the five membered ring and the radical attached in equatorial position and the aliphatic chain in gauche position. The second stable conformer has the aliphatic chain in anti position.     

Calculation of the vibration–rotational transition intensities of water molecules trapped in an argon matrix: stretching O–H vibrations spectral region

The frequencies and intensities of vibration–rotational transitions of water molecules in an argon matrix were calculated for temperatures of 6 and 30 K. The rigid asymmetric top approximation was used with available literature values of the effective rotational constants in the ground and excited vibrational states. The calculations were carried out by taking into account the existence of a non-equilibrium population distribution between the rotational levels of ortho- and para-water isomers. It was assumed that the temperature relaxation of the population of rotational levels is independent of the ortho- and para-isomers. Comparison of the results of the theoretical calculations with experimental literature data shows good agreement for the majority of the rotational structure lines for symmetric and antisymmetric stretching vibrations both in the frequency values and in the values of the relative intensities.     

Advances in wide bandgap SiC for optoelectronics

Silicon carbide (SiC) has played a key role in power electronics thanks to its unique physical properties like wide bandgap, high breakdown field, etc. During the past decade, SiC is also becoming more and more active in optoelectronics thanks to the progress in materials growth and nanofabrication. This paper will review the advances in fluorescent SiC for white light-emitting diodes, covering the poly-crystalline doped SiC source material growth, single crystalline epitaxy growth of fluorescent SiC, and nanofabrication of SiC to enhance the extraction efficiency for fluorescent SiC based white LEDs.     

Simultaneous second-harmonic generation with two orthogonal polarization states in periodically poled KTP

Simultaneous generation of second-harmonic light with orthogonal polarizations in the blue spectral region is demonstrated by use of typeII and typeI quasi-phase matching for the nonlinear coefficients d(33) , d(24) , and d(32) in periodically poled KTP. The second-harmonic power ratio in both polarization states can be tuned by the fundamental polarization and (or) the periodically poled KTP temperature. Femtosecond pulse frequency-doubling efficiencies of as much as 39.5% W (-1) and 8.1% W (-1) are demonstrated in 7-mm periodically poled KTP for typeI and typeII processes, respectively. The efficiency limitations caused by various effects of the group-velocity mismatch are discussed.     

Narrowband bulk Bragg grating optical parametric oscillator

A narrowband, pulsed optical parametric oscillator (OPO) whose output coupler is a bulk glass Bragg grating is demonstrated. The OPO is based on periodically poled KTiOPO4 and is pumped by a pulsed, frequency-doubled Nd:YAG laser at 532 nm, generating a signal at 975 nm with a total efficiency of 35%. This novel and compact device shows a spectral bandwidth of 0.16 nm (50 GHz), a decrease by a factor of 20 compared with that when a conventional mirror is used. By using a folded cavity, we demonstrate tunable radiation with a tuning range of 60 nm and maintained spectral bandwidth.     

Three-dimensional characterization of the effective second-order nonlinearity in periodically poled crystals

A novel technique for characterization of the second-order nonlinearity in nonlinear crystals is presented. It utilizes group-velocity walk-off between femtosecond pulses in type II SHG to achieve three-dimensional resolution of the nonlinearity. The longitudinal and transversal spatial resolution can be set independently. The technique is especially useful for characterizing quasi-phase-matched nonlinear crystals, and it is demonstrated in potassium titanyl phosphate.     

Optical parametric amplification in periodically poled KTiOPO(4) seeded by an Er-Yb:glass microchip laser

An optical parametric amplifier based on periodically poled KTiOPO(4) was used to generate 3-ns pulses at 1.544 mum . The device was pumped by a Q-switched Nd:YAG laser, and the signal output-pulse energy reached 71 muJ ; the maximum gain was 66 dB. The seed source was an Er-Yb:glass microchip laser. A theoretical fit to experimental data gave an effective nonlinear coefficient of 9.7 pm/V , close to the highest values reported for periodically poled KTiOPO(4) . Furthermore, the broad parametric gain observed could be used for broadband pulse amplification.