Showing papers in "Laser Physics Letters in 2005"

Fermi-Bose mapping for one-dimensional Bose gases

Abstract: One-dimensional Bose gases are considered, interacting either through the hard-core potentials or through the contact delta potentials. Interest in these gases gained momentum because of the recent experimental realization of quasi-one-dimensional Bose gases in traps with tightly confined radial motion, achieving the Tonks-Girardeau (TG) regime of strongly interacting atoms. For such gases the Fermi-Bose mapping of wavefunctions is applicable. The aim of the present communication is to give a brief survey of the problem and to demonstrate the generality of this mapping by emphasizing that: (i) It is valid for nonequilibrium wavefunctions, described by the time-dependent Schrodinger equation, not merely for stationary wavefunctions. (ii) It gives the whole spectrum of all excited states, not merely the ground state. (iii) It applies to the Lieb-Liniger gas with the contact interaction, not merely to the TG gas of impenetrable bosons.

Generation of Laguerre-Gaussian modes in Nd:YAG laser using diffractive optical pumping

Abstract: A beam of pulsed laser radiation at the wavelength λ = 0.532 μm was diffracted at a circular diaphragm to produce a hollow-shape intensity distribution in the near field. This light distribution was used to pump an Nd:YAG laser, resulting in the formation of an inversion profile with a minimum at the laser resonator axis and enabling the suppression of the fundamental mode. Under this condition, the oscillation at λ = 1.064 μm of Laguerre-Gaussian modes (LG0m) with low and high values of the azimuthal index m was produced in the gain-switching regime. By changing the geometry of the resonator, the size of its waist parameter was changed, enabling the selection of the mode with an index m that best overlaps with the inversion profile. Oscillation of LG0m modes with indices ranging from m=1 to more than m=200 was obtained. LG0m modes with m ≤ 50 were produced using the dependence of the waist parameter on the length of the resonator near the boundary of its stability region. A LG0m mode of the highest order, m ≈ 240 was obtained by building a miniature laser resonator and using a pair of diaphragms in order to form a sharper ring-shape pumping distribution. Applications of diffractive optical pumping and ``hollow'' LG0m laser beams are discussed.

Nd:YAG/V:YAG microchip laser operating at 1338 nm

Abstract: Q-switched microchip laser emitting radiation at wavelength 1338 nm was designed and constructed. This laser was based on a monolith crystal which combines in one piece a cooling undoped part (undoped YAG crystal), an active laser part (Nd3+:YAG), and a saturable absorber (V3+:YAG, T0=85%). The microchip resonator consists of dielectric mirrors directly deposited on the monolith surfaces. The output coupler with reflection 90% was placed on the V3+-doped part. Q-switched microchip laser was tested under pulsed, and CW diode pumping. The pulse length was the same for all regimes and it equals to 6.2 ns. The wavelength of linearly polarized laser emission was 1338 nm. For pulsed pumping the output pulse energy was stable up to mean pump power 1 W and it was equal to 131 μJ, which corresponds to peak power 21 kW. In CW regime for pumping up to 14 W the pulse energy was 37 μJ.

Bose‐Einstein condensates in fast rotation

Abstract: In this short review we present our recent results concerning the rotation of atomic Bose-Einstein condensates confined in quadratic or quartic potentials, and give an overview of the field. We first describe the procedure used to set an atomic gas in rotation and briefly discuss the physics of condensates containing a single vortex line. We then address the regime of fast rotation in harmonic traps, where the rotation frequency is close to the trapping frequency. In this limit the Landau Level formalism is well suited to describe the system. The problem of the condensation temperature of a fast rotating gas is discussed, as well as the equilibrium shape of the cloud and the structure of the vortex lattice. Finally we review results obtained with a quadratic + quartic potential, which allows to study a regime where the rotation frequency is equal to or larger than the harmonic trapping frequency.

S-band erbium-doped fiber ring laser using a fiber Bragg grating

Abstract: A short wavelength band erbium-doped fiber laser (S-band EDFL) is demonstrated utilizing a fiber Bragg grating (FBG) in unidirectional ring configuration. The amplification in S-band is achieved using an erbium-doped fiber with depressed cladding, which suppressed gains at longer wavelength. The laser operates at 1500 nm, which coincides with the FBG wavelength. The optimum EDFL operation is obtained by routing only 10% of the laser output into the cavity. The laser has an output power of 7.8 dBm, more than 60 dB of peak to floor separation and 3 dB bandwidth of less than 0.08 nm. This fiber laser provides an inexpensive source for tunable output in the wavelength range from 1480 to 1520 nm.

Stimulated Raman scattering in Nd:SrWO4

Abstract: Stimulated Raman scattering process in Nd:SrWO4 crystal was employed to frequency down-shift the fundamental frequency of a Nd:YAG mode-locked laser system. A single-pass configuration of Raman crystal was investigated for this purpose. After that Nd:SrWO4 laser was built and coherent pumping by alexandrite laser radiation was used. The simultaneous generation of stimulated Raman scattering was proofed for the case of Q-switching and mode-locking of Nd:SrWO4 Raman cavity. For Nd:YAG 50 ps long (1064 nm) pulsed pumping a single-pass first Stokes maximum energy and conversion efficiency were 1.6 mJ and 25% , respectively. With the free-running Nd:SrWO4 laser the maximum energy of 90 mJ at wavelength 1057 nm was obtained. Q-switching with the LiF:F-2 saturable absorber gave up to 1.3 mJ energy at the first Stokes frequency (1170 nm) in the pulse length of 3 ns. In mode-locking regime (with saturable absorber ML51 in dichlorethan or 3955 in ethanol), the total generated energy was 1.8 mJ and 2.4 mJ for ML51 and 3955 dyes, respectively. The SRS output at 1170 nm was approximately 20% of those values.

Stable laser-diode pumped microchip sub-nanosecond Cr,Yb : YAG self-Q-switched laser

Abstract: Near-diffraction-limited longitudinal multimode self-Q-switched microchip Cr,Yb:YAG laser is obtained by using of a laser diode as a pump source at room temperature without cooling Cr,Yb:YAG sample. The output Q-switched traces are very stable, and the slope efficiency is as high as 18.5%. Laser pulses with 23.5-μJ pulse energy and 440-ps pulse duration were achieved which results in over 53 kW peak power at repetition rate of 6.6 kHz. The effect of the absorbed pump power on the laser characteristics and laser spectrum are addressed in details. The number of the longitudinal laser modes increases with the absorbed pump power.

SRS risk potential in Faraday rotator Tb3Ga5O12 crystals for high-peak power lasers

Abstract: Hugh-order Stokes and anti-Stokes picosecond generation in the visible and near-IR in cubic Tb3Ga5O12 garnet crystal was observed for the first time. All scattering laser components were identified and attributed to the SRS-active vibration mode of this crystal.

Lifetimes of atomic Rydberg states by autocorrelation function

Abstract: We have derived the autocorrelation function for the field emitted by a Rydberg atom in a micocavity weakly excited in the strong coupling regime and in the non-resonant case. We propose simple analytical expressions and make use of them to determine the atomic frequency and the mean radiative lifetime of the Rydberg atom. As compared to direct measurements this method is promising.

Morphological evaluation of enamel and dentin irradiated with 9.6 μm CO2 and 2.94 μm Er:YAG lasers

Abstract: Background: The objective was to evaluate the morphology of enamel and dentin irradiated with Er:YAG (2.94 μm) and CO2 (9.6 μm) lasers. Methods: Six groups were evaluated: G1 – CO2 irradiated enamel (3 W); G2 – CO2 irradiated dentin (3 W); G3 – CO2 irradiated enamel (7 W); G4 – CO2 irradiated dentin (7 W); G5 – Er:YAG irradiated enamel (0.16 W); G6 – Er:YAG irradiated dentin (0.16 W). Results: The morphological pattern of Er:YAG laser irradiated enamel and dentin has a rough aspect with a clear exposition of the prisms and dentinal tubules. The melted surfaces covering the CO2 laser irradiated enamel and dentin, occlude the dentinal tubules and the enamel prisms. Conclusion: The rough pattern after Er:YAG laser irradiation, which originates from the micro-explosion of water, does not occlude the dentinal tubules, whereas the surface morphology after CO2 laser irradiation, which originated from the temperature rise above hydroxyapatite melting point, shows dentinal tubules occlusion and tissue melting. Clinical implications: These changes influence the tissue properties such as increase of the enamel acid resistance or decrease the bond strength between the tissue and composite resin.

Resonant scattering of a photon by an electron in the field of a circularly polarized electromagnetic wave

Abstract: This paper presents, for general relativistic case, a theoretical study of Compton effect in the field of a circularly polarized wave under resonant condition – resonances related to a virtual intermediate particle that falls within the mass shell We derive the expressions for the resonant amplitude and the differential cross section when the invariant intensity parameter of the wave is small (η << 1) and absent interference of the scattering and annihilation reaction amplitudes It is demonstrated that the resonant cross section of scattering may be several orders of magnitude higher than the cross section of Compton effect in the absence of the external field

Normal and anomalous averages for systems with Bose-Einstein condensate

Abstract: The comparative behaviour of normal and anomalous averages as functions of momentum or energy, at different temperatures, is analysed for systems with Bose-Einstein condensate. Three qualitatively distinct temperature regions are revealed: The critical region, where the absolute value of the anomalous average, for the main energy range, is much smaller than the normal average. The region of intermediate temperatures, where the absolute values of the anomalous and normal averages are of the same order. And the region of low temperatures, where the absolute value of the anomalous average, for practically all energies, becomes much larger than the normal average. This shows the importance of the anomalous averages for the intermediate and, especially, for low temperatures, where these anomalous averages cannot be neglected.

New mid IR (1.5–2.2 μm) Raman lasers based on barium tungstate and barium nitrate crystals

Abstract: Efficient mid IR (1.5–2.2 μm) Raman lasers based on novel BaWO4 and known Ba(NO3)2 Raman crystals were developed and investigated. Different Stokes shifted components were obtained with longest wavelength about 2.2 μm with efficiency up to 10%.

Measurements of Raman gain coefficient for barium tungstate crystal

Abstract: The Raman gain coefficient of a barium tungstate crystal was measured in the 532 nm to 1064 nm spectral region. The experimentally obtained data were fitted with the empirical equation, which takes into account the resonance electronic transitions.

Rubidium spectroscopy at 778–780 nm with a distributed feedback laser diode

Abstract: We have performed high resolution spectroscopy of rubidium with a single mode continuous wave distributed feedback (DFB) laser diode. The saturation spectrum of the D2-line of 85Rb and 87Rb was recorded with a resolution close to the natural line width. The emission frequency was actively stabilized to Doppler-free transitions with a relative accuracy of better than 7 parts in 109 using commercially available servo devices only. An output power of 80 mW was sufficient to allow for two-photon spectroscopy of the 5S-5D-transition of 87Rb. Further, we report on the spectral properties of the DFB diode, its tuning range and its frequency modulation properties. The line width of the diode laser, determined with high resolution Doppler free two photon spectroscopy, was 4 MHz without applying any active stabilization techniques. For time scales below 5 μs the line width drops below 2 MHz.

Ceramic Nd:YAG laser at 946 nm

Abstract: The third near infrared stimulated-emission spectral range of Nd:YAG ceramics at room temperature has been demonstrated. For the 4F3/2 → 4I9/2 transition emitting at 946 nm 1.35 W laser output have been achieved under 808 nm laser diode pumping at more than 20% efficiency similar as for crystalline material.

High efficiency continuous‐wave operation of a diode‐pumped Nd:GdVO4 laser at 1.06 µm

Abstract: The continuous-wave (cw) laser properties of an efficient diode-pumped Nd:GdVO4 crystal operating at 1.06 μm formed with a simple flat-flat cavity have been studied. With the incident pump power of 25 W, an output power of 15.6 W was obtained, with the optical conversion efficiency of 62.4% and the maximum slop efficiency of 71.3%.

Excitation and propagation of surface electromagnetic waves studied by terahertz spectrochronography

Abstract: We show the spectrochronography as an efficient tool to extend the THz time domain technique. Assuming that all the information is contained in the time-dependent electric field we apply a windowed transfer technique to measure the instantaneous spectra evolution. As an example, surface electromagnetic waves on the metal grating are considered. Dynamics of surface wave spectral component is measured.

Temperature-tuning Yb:YAG microchip lasers

Abstract: Based on the quasi-three-level system, a theoretical model of diode-laser end-pumped fundamental continuous-wave (CW) Yb3+:YAG microchip lasers is proposed. The fluorescence concentration quenching effect, the temperature dependent mechanical and optical properties and the absorption efficiency of the host have been taken into account in the model. The theoretical results of the numerical calculations are in good agreement with those of experiments. The effects of the concentration of the Yb3+:YAG crystal, the thickness of the Yb3+:YAG crystal, the temperature and the transmission of the output coupler on the laser performance (threshold and output power) are addressed. The optimization of the concentration and the thickness for the Yb3+:YAG crystal microchip laser is presented. The effects of the temperature and the pump power intensity on the optical-to-optical efficiency are discussed. The output power can be scaled by increase the working area of the laser gain medium. This modeling is not only applicable to Yb3+:YAG crystal microchip laser but also to other quasi-three-level microchip lasers.

Observation stimulated Raman scattering in nanocrystalline Sc2O3 ceramics

Abstract: Efficient room-temperature steady-state high-order stimulated Raman scattering under picosecond pumping was excited in highly transparent nanocrystalline ceramics based on cubic Sc2O3. All recorded Stokes and anti-Stokes lasing components in the visible and near-IR were identified and attributed to the χ(3)-active vibration mode ωSRS ≈ 419 cm-1 of this novel nonlinear-laser material.

1083 nm single frequency ytterbium doped fiber laser

Abstract: Single frequency 1083 nm ytterbium fiber laser was demonstrated by introducing loop mirror filter and polarization controller in linear laser cavity. The loop mirror with unpumped ytterbium fiber as a narrow bandwidth filter discriminated and selected laser longitudinal modes efficiently. Spatial hole burning effect was restrained by adjusting polarization controller appropriately. The laser linewidth was about 2 KHz. Output power up to 14 mW were obtained under the launched pump power of 100 mW at 976 nm, the corresponding optical-optical conversion efficiency was 14%, the slope efficiency was 18%. The measurement of RIN and power stability indicated the stable operation of the laser.

In vivo imaging of Malassezia yeasts on human skin using confocal laser scanning microscopy

Abstract: Fiber-based confocal laser scanning microscopy affords a vast field of application in medical research and clinical practice. The application of fluorescent dye allows real-time imaging of yeasts of the genus Malassezia on human skin in vivo. An Ar+-laser is used to excite the fluorescent food dye sodium fluorescein at 488 nm. Its emission is simultaneously detected in the spectral region from 500–600 nm. Topically applied fluorescein labels fungal microstructures in native habitat. Cumulative intradermal injection of the same dye enables a subsurface view of the underlying cutaneous area. In the present paper, we report the ability of the combination of in vivo confocal microscopy and sodium fluorescein application to produce real-time and high-resolution images of fungal structures on human skin. The obtained confocal images demonstrate the micro architecture of superficial Malassezia yeasts and corneocytes in horizontal plane. Taxonomic classification into different Malassezia species and observation of their colonisation patterns in native milieu brings new conclusions to fungal skin behaviour and diseases. We demonstrate advantages in clinical investigation practice over traditional laboratory routine using this non-invasive imaging tool. The described method opens new promising prospects and the possibility for further studies in fungal research.

Highly precise pulsed selective laser sintering of metallic powders

Abstract: We studied the influence of the laser parameters on the material properties of selectively laser sintered Titanium and Platinum-alloyed powders, which are both of paramount interest in modern technology. In this article, we show that with an appropriate energy deposition in the metallic powder layer, the material properties of the selectively laser sintered parts can locally be tailored to the requirements of the finished work piece. By adapting the laser parameters of a Q-switched Nd:YAG laser, notably pulse duration and local intensity, the degree of porosity, density and even the crystalline microstructure can be controlled. Pulsed interaction allows in addition to minimize the average power needed for consolidation of the metallic powder, and leads to less residual thermal stresses. With laser post processing, the surface can achieve bulk-like density. We also demonstrate for the first time to our knowledge the highly precise selective laser sintering of steel micro powder with a lateral accuracy of less than 10 micrometers by using a modelocked Nd:YAG laser. Furthermore, we present the possibility of forming metallic glass components by sintering amorphous metallic powders.

Study of experimental and numerical simulation of laser ablation in stainless steel

Abstract: In this paper, we present an experimental and theoretical study of pulse laser ablation of stainless steel target. Various parameters, such as laser power, pulse duration, enthalpy and heat capacity are used. The evaluation of which software will be suitable for the ablation processes has been done. The possibility to find micro-craters and microdefects was noted by using Reflection Optical Microscope (ROM). The ablation process induced by lasers is a collective phenomenon: that basically involves two phenomena: the laser radiation-with matter interaction and the dynamic of the ablation plume. A numerical solution is derived and stimulated for 2-D laser ablation process. Only the solid – liquid phase change is considered. This study contributes to a better understanding of the physical processes involved in the laser ablation targets.

Spatially incoherent modulational instability in a non local medium

Abstract: We study one-dimensional transverse modulational instability in a non local medium excited by a spatially incoherent source. Employing undoped nematic liquid crystals in a planar pre-tilted configuration, we investigate the role of the spectral broadening induced by incoherence in conjunction with spatially non local molecular reorientation. The phenomenon is modeled using the Wigner transform.

Absence of spin superradiance in resonatorless magnets

Abstract: A spin system is considered with a Hamiltonian typical of molecular magnets, having dipole-dipole interactions and a single-site magnetic anisotropy. In addition, spin interactions through the common radiation field are included. A fully quantum-mechanical derivation of the collective radiation rate is presented. An effective narrowing of the dipole-dipole attenuation, due to high spin polarization is taken into account. The influence of the radiation rate on spin dynamics is carefully analysed. It is shown that this influence is completely negligible. No noticeable collective effects, such as superradiance, can appear in molecular magnets, being caused by electromagnetic spin radiation. Spin superradiance can arise in molecular magnets only when these are coupled to a resonant electric circuit, as has been suggested earlier by one of the authors in Laser Phys. 12, 1089 (2002).

Nanosecond Nd:YAG laser on dental enamel: compositional analysis by X-ray fluorescence

Abstract: Non-invasive methods such as X-ray Fluorescence has been applied to study of the distinct pathologies and contamination levels analysis in various biological tissues among them nails, hair, and tooth. On the other hand, several works have demonstrated that the laser could be induced chemical and morphological alterations on the enamel surface occupying an important role as co-adjuvant in the caries disease prevention. Here, we have combined X-ray fluorescence using Fundamental Parameters method aiming to evaluate the variation in the chemical contend. The Ca and P concentrations as well as the Ca/P ratio were estimated in sound human and bovine enamel surface by X-ray fluorescence (XRF). We also evaluated the effect of the lactic and the acetic acids on the sound and irradiated bovine enamel surface by Scanning Electron Microscopy (SEM) verifying the acid attack changes in the sound and irradiated bovine enamel. The laser parameters applied produced lower ablation depths, but sufficient to induce compositional changes. Our results have indicating an alteration statically significative to Ca/P ratio and also indicated an increase in the Ca/P ratio for the irradiated groups in comparison to sound groups. We also verified that the acid attack is more pronounced to sound bovine enamel surface in relation to irradiated to the bovine enamel surface indicating that the nanosecond laser can be used to reduce the demineralization process.

Gain enhancement in partial double‐pass L‐band EDFA system using a band‐pass filter

Abstract: The partial double-pass L-band erbium-doped fiber amplifier with enhanced gain characteristic is demonstrated using a band pass filter (BPF). The BPF is incorporated in the double-pass route to suppress the amplified spontaneous emission from the single-pass output for gain enhancing. The gain of 51.5 dB is obtained for the proposed amplifier at input signal power of -40 dBm, which is approximately 5.2 dB higher compared with the system without the BPF. However, the insertion loss of the BPF contributes to a small noise figure penalty in the system. This amplifier can be easily modified to support dense wavelength division multiplexing system application by using multiple channel BPFs or interleaver.

Intramolecular charge delocalization and nonlinear optical properties of Methyl 3‐(4‐methoxy phenyl) prop‐2‐enoate from vibrational spectra

Abstract: The density functional computations of MMP are performed at B3LYP/6-31G (d,p) level to derive equilibrium geometry, vibrational wavenumbers and intensities, and first hyperpolarizability. Large NLO efficiency predicted for the first time in this new class of compounds has been confirmed by powder efficiency experiments. DFT calculation reveals that endocyclic angle at the junction of the propenoate group and the phenyl ring is decreased from 120° by 2.5°, whereas two neighbouring angles around the ring are increased by 2.1° and 1.2° respectively, associated with intramolecular charge transfer interaction. The vibrational spectra confirm the charge transfer interaction between -COOCH3 group and phenyl ring through the ethylenic bridge with simultaneous infrared and Raman activation of C7=C18 stretching and ring modes 8 and 19. The large intensity differences observed between 8a and 8b modes in both IR and Raman spectrum due to the algebraic difference of the electronic effects of the substitutents have been discussed. The charge transfer interaction between -COOCH3 group and phenyl ring through the ethylenic bridge resulting in π-electron cloud movement from donor to acceptor can make the molecule highly polarized and must be responsible for the NLO activity of MMP.

The Coulomb-repulsion compensation between the ions of the beam in the presence of a strong pulsed laser field

Abstract: The Coulomb-repulsion compensation of classical nonrelativistic hydrogen ions in the beam in crossover in the presence of a strong pulsed laser field with an intensity of about 10 15 W/cm 2 is theoretically studied. It is demonstrated that the average effective interaction force can fundamentally differ from the Coulomb law.