Fundamental Laser Wavelength Research Articles

Phase control over decaying molecular states in intense laser pulses

A time-dependent approach to study phase control over molecular photoabsorption, provided by intense laser pulses, is elaborate. The method allows for the decay linewidth of molecular states and frequency bandwidth of the controlling laser field, and can be applied in weak and strong laser fields where the perturbation theory is invalid. It is shown that a frequency mismatch between the fundamental laser wave and its third harmonic can destroy control. For the example of the one-photon versus three-photon control a simple picture of interference from two monochromatic absorption pathways is not enough to explain phase control and one needs to consider a nonlinear temporal interference of multiquantum transitions. In the perturbation-theory limit an elegant generalization of the famous Shapiro-Hepburn-Brumer equation for the one-photon versus three-photon control is derived. Various numerical calculations illustrate the dependence of phase control on molecular linewidth, fundamental laser wavelength, pulse duration, and peak intensity. It is obtained, that the one-photon versus three-photon control is productive if the molecular state populations, individually produced by each laser wave, have beats of approximately the same frequency. The calculations demonstrate that an enough intense optical pulse can suppress molecular decay and may be used in order to keep stable the state population of a decaying molecule for a long time. The available experimental results for the one-photon versus three-photon control over simple and large polyatomic molecules are analyzed and recommendations for the experimental improvement of control are formulated.

유기재료의 이상분산을 이용한 파장변환

Second harmonic generation(SHG) by guided phase matching is observed in waveguide structure using the anomalous dispersion of a poled polymer. The second harmonic TM guided mode could be generated from the fundamental TM guided mode and then the second harmonic power was higher than any other phase matchable mode because the overlap integral between the fundamental and the second harmonic wave was the largest in the theoretical analysis. Near UV SHG(370 nm) was obtained from the fundamental wavelength of Ti-sapphire laser(740 nm).

Highly efficient narrow-line generation by difference-frequency mixing of a green pump and the stokes seed in RbTiOPO4 crystals: excitation of 943-nm emission.

An efficient and compact scheme for diode-pumped Nd:YLF laser wavelength conversion to 943 nm was demonstrated by use of difference-frequency mixing and stimulated Raman scattering. We believe that this is the highest conversion efficiency from the laser fundamental wavelength reported to date. It is shown that RbTiOPO4 crystals are capable of providing highly efficient frequency mixing as a nonlinear medium.

The nonlinear interaction of waves generated by the stimulated Raman scattering with plasma in the PALS experiment for the laser wavelength 438 nm

This paper is devoted to the study of the nonlinear interaction of waves generated by the stimulated Raman scattering with plasma in the PALS experiment. We solve problem of the influence of nonlinear interaction of plasma wave with particles on the sum of actions generated by the laser wave. Numerical value of the change of the electric field of the quasimode determined by beating of forward and backward plasma waves of Raman scattering given by trapping of plasma particles in the PALS experiment is calculated, too. Numerical values are obtained for typical parameters of the PALS experiment, but for the laser wavelength at vacuum λ=438 nm (no for the fundamental wavelength of the laser ASTERIX). The nonlinear effects are greater than the same effects determined by the fundamental laser wavelength.

Second-harmonic generation in periodically poled GaN

We report the experimental demonstration of second-harmonic generation in periodically poled GaN by first-order quasiphase matching. The periodically poled structure was grown by plasma-assisted molecular-beam epitaxy. We observed about 9 μW of second-harmonic power from a fundamental input laser wavelength of 1658.6 nm with a normalized conversion efficiency of 12.76% W−1 cm−2. The ability to perform nonlinear wavelength conversion by periodic poling and the fact that GaN has a very wide window of transparency, pave the way for GaN to be used for nonlinear optical devices in telecommunications as well as a nonlinear light source for biochemical detection in the far infrared and deep ultraviolet.

Wide-spectral-range laser refractometer.

We present refractometric measurements made in the 266-1064-nm spectral region with a pulsed Nd:YAG laser, and the second, third, and fourth harmonics of the laser's fundamental wavelength. The critical angle is determined by the disappearance of the diffraction orders from a metal grating, forming a microcuvette with the prism's reflecting wall. A fused-silica measuring prism is used in the experiments.

Synthesis and second order nonlinear optical properties of new chromophores containing 1,3,4-oxadiazole and thiophene rings

We report the synthesis and physico-chemical characterization, including molecular second order nonlinear optical properties by the EFISH technique, of three new heterocycle based push–pull chromophores. Two chromophores contain the five membered 1,3,4-oxadiazole ring, the third a thiophene ring. The chromophores also contain azo or stilbene bridges between conjugated aromatic rings and are functionalized for covalent incorporation into polymer chains. The maximum observed μgβ is 1350 × 10−48 esu for the thiophene chromophore in conditions far from resonance enhancement (fundamental laser wavelength 1.907 µm). The crystal structure of one oxadiazole chromophore is also discussed.

Spontaneous and stimulated emission of Nd3+ in the nonlinear crystal Gd0.2Y0.8Al3(BO3)4

The spontaneous and stimulated emission of Nd3+ ions in Gd0.2Y0.8Al3(BO3)4 have been investigated as an alternative system to the well-known YAl3(BO3)4 nonlinear host laser crystal. An emission peak cross-section value of 1.8×10−19 cm2 (at 1062 nm) has been determined from spontaneous emission spectra. A lifetime of 54 μs was measured. Stimulated emission has also been demonstrated in a continuous wave Ti-Sapphire end pumped cavity. From these experiments, the optical loss factor (L=5% cm−1) and the effective emission cross-section (σef=1.8×10−19 cm2) have been determined. A weak signal (≤1 mW) of coherent green radiation (self-frequency doubling of the fundamental laser wavelength) was also observed under non optimal phase matching conditions.

Low-Noise Blue Light Generation from an Intracavity Frequency Doubled LD-Pumped Cr:LiSrAlF6 Laser by a Multi-Mode Method.

We report a new method to reduce the output power noise of an intracavity second harmonic generation (SHG) laser at 430 nm. LiB3O5 (LBO) nonlinear crystal was inserted into the cavity of a laser diode (LD) -pumped Crdoped LiSrAlF6 (Cr: LiSAF) laser for blue light generation. The maximum SHG output power was 38mW, asgenerated from the oscillation of the fundamental wave in a multi-longitudinal mode. High output stabilitywas observed at an output power of 30.5mW±1% for more than 10hours. We investigated the standingwave condition at the fundamental laser wavelength by calculating the intensity distribution inside the cavityresonator. The laser crystal was arranged at a proper position inside the cavity so that each standing waveremained in the multi-mode and did not fall into competition, and a low-noise blue light output was obtainedin the multi-mode.

Near UV Second Harmonic Generation using Anomalous Dispersion of Poled Polymer

Second harmonic generation (SHG) by guided phase matching using anomalous dispersion of poled polymer is investigated in waveguide structure. The second harmonic TM0 guided mode can be generated from the fundamental TM0 guided mode and then the second harmonic power was higher than any other phase matchable mode because the overlap integral between the fundamental and the second harmonic waves is the largest in theoretical analysis. Near UV SHG (370nm) was observed from the fundamental wavelength of Ti-sapphire laser (740nm).

Red, green, and blue laser light from a single Nd:YAl3(BO3)4 crystal based on laser oscillation at 1.3 μm

Laser radiation corresponding to the three fundamental colors (red, green, and blue) has been generated from the same Nd:YAl3(BO3)4 crystal, operating on a fundamental laser wavelength of 1338 nm in an end-pumping configuration. Continuous wave generation was obtained by pumping with a tunable Ti: sapphire laser. Red (669 nm) has been obtained by self-frequency doubling of the fundamental laser line. Green (505 nm) and blue (481 nm) have been obtained by self-sum-frequency mixing of the fundamental laser radiation at 1338 nm and the pump radiation (807 nm for green and 755 nm for blue).

Crystal growth and defects characterization of zinc tris (thiourea) sulfate: a novel metalorganic nonlinear optical crystal

Single crystals of the metalorganic nonlinear optical material zinc tris (thiourea) sulfate (ZTS) were grown from aqueous solution. The morphology of the crystals was indexed. The grown crystals were characterized by recording the powder X-ray diffraction pattern and by identifying the diffracting planes. Spectrophotometric studies on ZTS reveal that it has good transparency for the Nd: YAG laser fundamental wavelength. Differential thermal analysis of ZTS indicates that the material does not sublime before melting but decomposes immediately after melting. The defect content of the crystals was estimated using etching and X-ray topography. The mechanical hardness anisotropy was evaluated in the (100) plane, which indicates the presence of soft directions.

Production of gold cluster ions by laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry

We report a simple method for generating large gold cluster ions, Au +/-, by laser desorption Fourier-transform ion cyclotron resonance (LD FT-ICR) mass spectrometry. The gold clusters are generated from peptide-covered thin gold films coated on glass plates to ≈ 10 nm thickness to provide for high optical absorbance at the Nd:YAG laser fundamental wavelength, 1064 nm. Abundant negatively charged gold clusters up to Au - 46 are produced when gramicidin S peptide is overcoated on the gold film. These gold cluster ions are the largest reported to date by laser desorption without use of a supersonic jet expansion source.

Polyphenothiazinobisthiazole: A novel polymer for third‐order nonlinear optics

AbstractThe synthesis and the optical properties of the novel polymer polyphenothiazinobisthiazole (PPT) are described. The design of this polymer was planned taking into consideration several aspects that were anticipated to lead to a material with an enhanced nonlinear optical susceptibility (χ(3)). Monomer 16 was prepared in a five‐step synthsis starting from N‐dodecyl‐3,7‐diaminophenothiazin (11). 16 was reacted with terephthaloyl chloride to yield the precursor polyamide 17. This precursor polyamide was subjected to a thermal cyclization at 300°C under vacuum leading to the title polymer PPT (18). PPT shows UV/vis absorption maxima at λ=282 nm, 305 nm and 463 nm. The macroscopic nonlinear optical susceptibility χ(3)(−3ω;ω,ω,ω,) of a thin film of PPT was determined with a third harmonic generation (THG) technique at a fundamental laser wavelength λL=1064 nm. The results show that PPT exhibits nonlinear optical properties comparable to those of poly‐p‐phenylenevinylene (PPV).

Acousto-optic actively mode-locked frequency-doubled continuous-wave Nd:YAG laser

We report a 200-MHz ultrahigh frequency acousto-optic mode-locked and KTiOPO4 stable intracavity frequency-doubled Nd:YAG laser pump source, which included a single-lens telescopic and L-type folded-arm resonator. 20 W high average mode-locked power and 2.0 W average mode-locked doubled green light power achieved at 4.0 kW single lamp pumped power, respectively. The instability of second-harmonic light output power was effectively suppressed by inserting a quarter wave plate at the fundamental laser wavelength inside the cavity.

Epitaxial Waveguiding KNbO3 Thin Films Grown By RF-Sputter Deposition

AbstractThe physical and optical properties of KNbO3 layers grown on (001) oriented spinel and MgO substrates by planar rf-sputter deposition were studied. Rutherford Backscattering measurements showed that stoichiometric films could be obtained by using K2CO3 enriched targets and 100% argon as a sputtering gas. The x-ray diffraction spectra showed that single crystalline tetragonal films could be obtained at temperatures in the range of 580–610°C. Furthermore, channelling experiments indicated good crystal quality with a χmin of 40%. High resolution Transmission Electron Microscopy of the films revealed epitaxial growth, but also domains with a typical width of 10–20 nm. Moreover, it was possible to excite waveguide modes with losses of only 1.1 dB/cm at λ = 632.8 nm. The nonlinear optical coefficient d31 was determined by the Maker-fringe technique using the 1.06 μm Nd:YAG laser fundamental wavelength. This yielded a d31 value of 5 pm/V. The electro-optic properties was investigated by phase modulation technique in a Michelson interferometer.

Generation of pulsed squeezed light in a mode-locked optical parametric oscillator

The generation of pulsed squeezed light using an optical parametric oscillator (OPO) is discussed. This mode-locked optical parametric oscillator consists of a nonlinear crystal in a cavity which is resonant for both signal and idler waves and which is synchronously pumped by the second-harmonic of an acousto-optically mode-locked cw Nd: YAG laser. The fundamental wavelength of the pump laser provides local oscillator pulses for balanced homodyne detection of squeezed vacuum pulses emitted by the oscillator when operated below oscillation threshold. Photocurrent noise reduction to 30% below the classical shot-noise limit is observed, corresponding to squeezing of the field to a level approximately a factor of two below the mean square vacuum noise.

Sputter deposition of epitaxial waveguiding KNbO3 thin films

Thin, stoichiometric KNbO3 layers were sputter deposited onto (100)-spinel and (100)-MgO substrates at a substrate temperature of 610 °C. The composition of the layers was determined by Rutherford backscattering (RBS) measurements. Potassium stoichiometry was maintained by an enrichment of the target with K2CO3. Furthermore, channeling experiments indicated good crystal quality with a χmin of 40%. The x-ray diffraction spectra showed single-crystalline tetragonal films. Waveguide modes with losses of only 1.1 dB/cm at λ=632.8 nm could be excited in the sputtered films. The nonlinear optical coefficient d31=5 pm/V was determined by the Maker-fringe technique using the 1.06 μm Nd:YAG laser fundamental wavelength (compared to d31=15 pm/V measured in orthorhombic single crystals).

Direct measurement of the N 2 + dissociation energy

The accuracy for the direct measurement of the dissociation energy of the N 2 + B2Σ u +-state was significantly improved by using frequency doubled laser light, which enables the authors to excite from lowerv″-levels and additionally to calibrate the fundamental laser wavelength with an iodine cell. The obtained value is:D8(N 2 + )=70248±6 cm−1.

Repetitively Q-Switched Nd:YAlG–LiIO3 0.53-μ Harmonic Source

LiIO3 placed inside the cavity of an acousto-optically Q-switched, tungsten-pumped Nd:YAlG laser has been employed to generate kilohertz repetition rate pulses at 0.532 μ. The peak output power of 855 W obtained in the TEM00 mode at a repetition rate of 1 kHz was about 1.5 times greater than that available from the same laser at the fundamental laser wavelength, 1.064 μ. Volume damage occurred in the LiIO3 typically after several hours of operation at 1 kHz, an improvement over Ba2NaNb5O15.