Line shapes of near-infrared DFB and VCSEL diode lasers under the influence of system back reflections

Laser diode line widths and line shapes are experimentally investigated in dependence on the diode current and on back reflections from an optical system. Four distributed-feedback (DFB)-type diode lasers and two vertical-cavity surface-emitting lasers (VCSELs) have been tested within the same optical setup and using the same fitting methods. System back reflection ratios of light reflected back to the laser have been varied between ?1?dB and ?45?dB and were below ?60?dB when all reflections were blocked. The background of this investigation is the evaluation of different laser types with respect to their suitability for sensor applications in which optical back reflections may occur, for example tunable diode-laser spectroscopy (TDLS). While DFB-type lasers showed almost pure Lorentzian line shapes and line widths of a few MHz, the tested VCSELs had a strong Gaussian contribution to the line shape, indicating stronger 1/f noise, which was also observed in the relative intensity noise of these particular lasers. System reflection ratios above ?25?dB had strong effects on the line width in both DFB diode lasers and VCSELs, while some influences have been observed at even lower reflection ratios for DFB diode lasers. As much smaller reflection ratios are typically required in TDLS systems to avoid etalon-like fringes and self-mixing interference effects, we conclude that the influence on the line width is not the most important reason to minimize back reflections in practical TDLS systems or to choose one type of diode laser over the other.     

Resolution enhancement in a light-sheet-based microscope (SPIM)

Light-sheet-based microscopy [single-plane illumination microscope (SPIM)] performs very well at low numerical apertures. It complements conventional (FM), confocal (CFM), and two-photon fluorescence microscopy (2hnu-FM) currently used in modern life sciences. Lateral and axial SPIM point spread function (PSF) extents are measured by using fluorescent beads to determine the 3D resolution. The results are compared with values derived from an analytical theory and numerical simulations. The discrepancies are found to be less than 5%. The axial extent of a SPIM-PSF (10x/0.3 W) is approximately 5.7 microm. This value is almost a factor of 2 smaller than in CFM, more than 2.5 times smaller than in FM, and more than three times smaller than in 2hnu-FM. SPIM outperforms 2hnu-FM and FM, while CFM has a better axial resolution at NAs above 0.8.     

Similariton fiber laser with a hollow-core photonic bandgap fiber for dispersion control

We report on an ytterbium-doped similariton fiber ring laser with a hollow-core photonic bandgap fiber for intracavity dispersion control. The oscillator is hybrid mode locked with a saturable Bragg reflector and by nonlinear polarization evolution. This scheme allows for an exact adjustment of the transmission characteristic to avoid the formation of bunched noiselike pulses while the self-starting characteristic is preserved. The oscillator generates highly stretched similaritons at 1025 nm with a pulse energy above 1n J at a repetition rate of 21.9 MHz.     

One-dimensional deformation waves in nonlinear viscoelastic media

This paper is concerned with wave propagation processes in viscoelastic media. The constitutive equation is assumed to be dependent on the strain history, and physical and geometrical nonlinearities are taken into account. Using two equivalent forms of the constitutive equation, the corresponding transport equations are derived along the characteristics of a linear associated process. The high-frequency and low-frequency processes are investigated by making use of the asymptotic transport equations. The similarity of the results obtained by this method and by the singular surface theory is shown and the critical strain gradients derived by both methods are compared. The influence of inhomogeneity of the medium is discussed.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

Negative-parity spectra for mass-18 nuclei in the dynamic-interaction propagator approach

The energy spectra and two-particle strengths of negative-parity states in mass-18 nuclei are calculated by using a Green-function formulation which includes energy-dependent two-particle interactions. The energy dependence is induced by the dynamic exchange of the octupole phonon which appears at 6.13 MeV in ¹⁶O. This state is described within a normal static particle-hole RPA. The two-body interaction parameters are chosen to provide the correct phonon energy and reasonable negative parity mass-17 and positive-parity mass-18 spectra. The negative-parity states are then calculated in a parameter-free way. In order to avoid redundant solutions or ghosts, the fermion lines must be dressed in a way consistent with the phonon exchange.     

Long-time behaviour of soliton ensembles. Part I––Emergence of ensembles

This paper is focused on the emergence of the KdV solitons from an initial harmonic excitation. In the long run this process is characterized not so much by regular soliton trains but rather by soliton ensembles. It has been shown explicitly that under indicated initial conditions the width of emerging solitons are mostly larger than the distance between maxima of wave profiles. Consequently, visible are the ensembles formed by several simultaneously interacting solitons including also hidden (virtual) solitons. The conditions for emerging such ensembles are studied over the wide range of amplitude ratios for typical dispersion parameters. Based on that analysis, it is possible to cast more light to the recurrence and periodicity in the long run (see Part II).