Harmonic Generation Of Light Research Articles

Detection and light enhancement of glucose oxidase adsorbed on porous silicon microcavities

AbstractPorous silicon (PSi) structure is used as support material to detect protein infiltration and to induce fluorescence and second harmonic light enhancement from glucose oxidase (GOX). Functionalization and protein infiltration is monitored by specular reflectometry. Optical response enhancement of PSi microcavity structures compared to PSi single layers or Bragg mirrors is observed, when GOX is impregnated. Penetration of organic molecules along the PSi microcavity structure is demonstrated by energy dispersive X‐ray profile. Enhanced fluorescence emission of GOX when adsorbed on PSi microcavity is evidenced by multi‐photon microscopy (MPM). Second harmonic light generation is observed at some particular pores of PSi and subsequent resonance enhancement of the signal arising from the GOX adsorbed within the pores is detected. Our work evidences an improved device functionality of GOX‐PSi microcavities due to strongly confined and localized light emission within these structures. This opens the way towards the application of PSi microcavity structures as amended biosensors based on their locally enhanced optical response. The second main achievement lies in the novelty of the used techniques. In contrast to the specular reflectometry used to monitor the macroscopic optical response of PSi structures, MPM presents a valuable alternative microscopic technique probing individual pores. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

UV Second Harmonic Generation at 266 nm in He+ Implanted β-BaB2O4 Optical Waveguides

We report on the second harmonic generation of deep UV light in beta -BaB(2)O(4) (BBO) waveguides pumped by a frequency-doubled continuous-wave Nd:YAG laser. An output power of 0.32 mW at 266 nm has been achieved for an internal pump power of 670 mW. Optical channel waveguides in BBO crystals were produced by He(+) ion implantation, lithographic masking and ion etching. The linear and nonlinear optical properties and the power handling capability of these waveguides are presented.

UV integrated optics devices based on beta-barium borate

We report on our recent progress in development of ultraviolet (UV) integrated optics devices based on beta-barium borate (BBO). Planar optical waveguides with a thickness of a few micrometers have been formed by the implantation of He+ ions with energies of around 2MeV. Two alternative methods based on the femtosecond-laser assisted micromachining and lithographic structuring for the fabrication of ridge-type channel optical waveguides in implanted BBO crystals have been developed, and the transmission properties of the obtained waveguides have been studied. We demonstrate a big potential of the fabricated channel waveguides for the second harmonic generation of continuous-wave deep-UV laser light with a power of the order of 1mW, exploiting the nonlinear optical properties of BBO crystal. In addition, a low-voltage electro-optic waveguide modulator for the deep-UV light (half-wave voltage times electrode length Vπ×l=43Vcm at 257nm) was realized for the first time.

Fabrication of periodically polarity-inverted ZnO films

One-dimensional periodically polarity-inverted (PPI) structures of ZnO for nonlinear optical devices are fabricated on c-plane Al2O3 substrates. To do so, corrugated MgO buffer layers are fabricated by etching after patterning, which is followed by the growth of ZnO layers by plasma-assisted molecular beam epitaxy. The polarity-inverted structures are confirmed by scanning piezoresponse microscopy and atomic-force microscopy. PPI structures with submicron periodicity are fabricated to satisfy the quasiphase matching condition for second harmonic generation of light.

Time resolved measurements of melting and solidification in Si using third harmonic generation of light

Time resolved measurements of melting and solidification on (001) Si using third harmonic generation (THG) were performed with subpicosecond time resolution. Following 120fs laser pulses at fluences above the melt threshold, the circularly polarized THG signal decreases by over three orders of magnitude. It regains its original intensity on solidification after ≈2ns. The authors show that the THG signal is sensitive to specimen temperature, decreasing by a factor of ≈5 between 298K and the melting temperature. The work demonstrates that complete thermal and phase histories can be obtained during ultrafast laser heating using single-shot THG experiments.

Second harmonic generation in the near field and far field: A sensitive tool to probe crystalline homogeneity

In order to probe crystalline orientation of SrxBa1−xNb2O6 (SBN:x) thin film, we have developed a detection scheme based on a scanning near-field optical microscope (SNOM). It is used to image simultaneously the fundamental and the second harmonic generation (SHG) of light by the sample under pulsed laser illumination. We demonstrate on SBN thin films that an apertureless SNOM can dramatically improve the resolution and the sensitivity of SNOM-SHG. Tip direction and focalization are the two crucial parameters in the SNOM-SHG experiments. Moreover, we show the ability of our setup to separate near field from far field contribution to the SHG. This is indeed very helpful in order to measure surface-SHG coefficients.

Second harmonic generation of continuous wave ultraviolet light and production of β-BaB2O4 optical waveguides

We report on the generation of continuous-wave (cw) ultraviolet (UV) laser light at λ=278nm by optical frequency doubling of visible light in β-BaB2O4 waveguides. Ridge-type waveguides were produced by He+ implantation, photolithography masking, and plasma etching. The final waveguides have core dimension of a few μm2 and show transmission losses of 5dB∕cm at 532nm and less than 10dB∕cm at 266nm. In our first experiments, a second harmonic power of 24μW has been generated at 278nm in an 8mm long waveguide pumped by 153mW at 556nm.

TRIUMF resonant ionization laser ion source

The range of isotopes available at the TRIUMF Isotope Separator Accelerator (ISAC) facility has been greatly enhanced by adding a Resonance Ionization Laser Ion Source (RILIS). A large wavelength range is accessible with the fundamental, second and third harmonic generation of titanium-sapphire laser light. In addition a dedicated laser is available for non-resonant laser ionization. The first online beam 62Ga was delivered in Dec. 2004. In general RILIS improves the intensity, purity and emittance of ion beams. 62Ga and 26Al and Be beams have been delivered so far on-line.

Nonlinear Mie scattering from spherical particles

A theoretical analysis of the second harmonic generation of light from spherical particles is presented that unifies existing theories which are valid in the special cases of small particle size (Rayleigh limit), small refraction index, radiation by nonlocal dipole and quadrupole moments. We study the angular distribution of second harmonic using a nonlinear generalization of the linear Mie theory.

Violet light second harmonic generation and optical properties of the nonlinear optical organometallic ZnCd(SCN) 4 crystal

We report on continuous-wave violet-blue light generation by direct frequency doubling a laser diode in a ZnCd(SCN) 4 crystal. 10.3 mW second harmonic generation light at 404 nm is generated with a fundamental power of 1.46 W incident on 3-mm-long crystal. The d 14, d 15 nonlinear optical coefficients of the crystal were also determined by the Maker fringes method at 1064 nm.

Transparent Ferroelectric Glass-Ceramics*

In recent years, there has been a resurgence of interest in transparent ferroelectric glass-ceramics (TFGCs), which are a special class of glass-ceramic composites that combine the low cost of fabrication and forming of transparent glass with the superior nonlinear optical and electro-optical properties of ferroelectric crystals. In this paper, we present a review of the current status, focusing on the challenges of fabrication and opportunities for selectively creating nonlinear optical structures, which will be useful in realizing integrated optical devices. A successful fabrication of TFGC requires the nucleation and growth of crystallites that are too small to scatter light, yet large enough to have ferroelectric response. Early experiments on silica based glasses containing common ferroelectric oxides indicated that although the preparation of TFGC is feasible, such a balance of crystallite size is difficult to achieve. However, later studies have demonstrated successful fabrication of TFGCs with compositions based on high refractive index glass matrix (e.g. tellurites containing ferroelectric LiNbO3), or the ferroelectric oxides that form glass easily and then crystallize congruently (e.g. LaBGeO5). Surface crystallization dominates the devitrification of these compositions. Strong second harmonic generation of light has been observed in a number of glass-ceramic systems, which makes them attractive for applications but so far the ferroelectric behavior has been demonstrated for very few systems.

Synthesis, characterization and evaluation of nonlinear optical properties of chiral hydrobenzoin monomers

Four new monomers have been synthesized by condensation of the chiral pure reagents (R,R)-(+)-1,2-diphenyl-1,2-ethanediol and (S,S)-(–)-1,2-diphenyl-1,2-ethanediol ((R,R)-(+)-hydrobenzoin and (S,S)-(–)-hydrobenzoin, respectively) with methacryloyl chloride with the purpose of preparing structures that exhibit second harmonic generation of laser light and to polymerize them by free radical polymerization. The monomers (R,R)-(+)-1,2-diphenyl(2-methacryloyloxy)ethanol, (S,S)-(–)-1,2-diphenyl(2-methacryloyloxy)ethanol, (R,R)-(+)-1,2-diphenyl(1,2-dimethacryloyloxy)ethane and (S,S)-(–)-1,2-diphenyl(1,2-dimethacryloyloxy)-ethane were obtained and characterized by melting point measurements, infrared spectroscopy, nuclear magnetic resonance spectroscopy, gas chromatography with mass spectroscopy and polarimetry. The optical properties evaluation was made following the Kurtz and Perry modified procedure in powder form and using a Nd:YAG laser as pulse light source (≈ 0.466 mJ/mm2) at 1064 nm. The second harmonic generated light (532 nm) from each compound was compared with the calibration spectrum of a chiral compound (saccharose or sucrose, know as sugar) used as a standard. The second harmonic generation values measured showed that R,R (+)-1,2-diphenyl(2-methacryloyloxy)ethanol and (S,S)-(–)-1,2-diphenyl(2-methacryloyloxy)ethanol enantiomers had better efficiency of second harmonic generation than (R,R)-(+)-1,2-diphenyl(1,2dimethacryloyloxy)ethane and (S,S)-(–)-1,2-diphenyl(1,2-dimethacryloyloxy)ethane under the same conditions. In other words, the monoacylation products worked much better than the diacylation products or the hydrobenzoin enantiomers themselves from the SHG behavior point of view.

Harmonic violet light generation in periodically poled bulk near-stoichiometric MgO-doped LiNbO 3

By the method of vapor transport equilibration, high optical quality 1.8 mol% MgO-doped near-stoichiometric LiNbO 3 (Mg:SLN) crystals were grown. A uniformly periodic domain structure in a 1.0 mm thick slab of Mg:SLN was fabricated by applying external pulsed field. Using a Ti:sapphire laser with a pulse width of 60 fs and a repetition rate of 82 MHz, third-order quasi-phase-matched second harmonic violet light generation was demonstrated by free propagation of 800 nm fundamental beam in a 12 mm long Mg:SLN slab at room temperature, with an energy conversion efficiency of 20.5%.

Infrared-phonon-polariton resonance of the nonlinear susceptibility in GaAs.

Nonlinear probing of the fundamental lattice vibration of polar crystals is shown to reveal insight into higher-order cohesive lattice forces. With a free-electron laser tunable in the far infrared we experimentally investigate the dispersion of the second-order susceptibility due to the phonon resonance in GaAs. We observe a strong resonance enhancement of second harmonic light generation at half the optical phonon frequency, and in addition a minimum at a higher frequency below the phonon frequency. Measuring this frequency and comparison to a theoretical model allows the determination of competing higher-order lattice forces.

Second Harmonic Generation of Light in Doped Ferroelectric Polymer Films

Second-order nonlinear optical properties in polymeric system of the "host-guest" type are investigated. The ferroelectric copolymers of vinylidene fluoride with trifluoroethylene P(VDF/TrFE) are used as the polymeric matrix. P(VDF/TrFE) were doped by donor-acceptor molecules of Dispersion Orange Dye 3 (DO3). The second harmonic generation (SHG) is caused by the nonlinear polarizability of conjugated molecules containing donor and acceptor para-substituents. The temperature dependence of SHG in the region of phase transition from ferroelectric to paraelectric phase of P(VDF/TrFE) has been investigated. A manifestation of ferroelectric behaviour in the SHG in doped copolymer has been shown.

New adjustment technique for time coincidence of femtosecond laser pulses using third harmonic generation in air and its application to holograph encoding system

The third harmonic generation of light (266 nm) is enhanced, sensitively depending on the time delay between a pair of pulses split from a single 800 nm femtosecond laser pulse, when they are focused and collided in air. This finding offers a convenient and widely applicable technique to detect temporal and spatial overlapping of two femtosecond pulses. This technique has several advantages over the conventional sum frequency generation method using nonlinear optical crystals, since it obviates the need for expensive crystals, free from phase matching, and elimination of temporal walk off. By applying it to “a holographic encoding system using an interference femtosecond laser pulse,” a periodic fringe spacing is minimized to ∼430 nm by extending the colliding angle between two-pulse beams up to ∼160 °C.

Second harmonic generation of light in the Kretschmann attenuated total reflection geometry in the presence of surface roughness

Using a computer simulation approach we study the generation of second harmonic light in reflection and in transmission in the Kretschmann attenuated total reflection geometry. In this geometry a thin metal film is deposited on the planar base of a dielectric prism, through which p-polarized light is incident on the film. The back surface of the film, which separates the film from vacuum, is a one-dimensional, randomly rough surface, whose generators are normal to the plane of incidence of the light. The nonlinearity responsible for the second harmonic generation is assumed to arise at the prism-metal and metal–vacuum interfaces, and thus enters the problem only through the boundary conditions at these interfaces at the harmonic frequency. The source terms entering these boundary conditions are obtained from the solutions of the corresponding scattering and transmission problems at the fundamental frequency. It is found that a peak in the angular dependence of the intensity of both the transmitted and reflected second harmonic light occurs in the directions normal to the mean scattering surface, in addition to an enhanced backscattering peak in the retroreflection direction. The enhanced transmission peak occurs in the non-radiative region, and therefore cannot be observed in the far field.

Ultraviolet Light Generation in a Periodically Poled MgO:LiNbO3 Waveguide

We demonstrated the highly efficient UV light generation of 386 nm wavelength in a periodically poled MgO:LiNbO3 waveguide. Utilizing multiple short pulses for electric poling to off-cut MgO:LiNbO3, we succeeded in fabricating a uniform periodically poled structure with a period of 2.2 µm and a thickness of 1.5 µm over a 10 mm interaction length. By using this structure with a waveguide, the harmonic ultraviolet light generation with a high conversion efficiency of 1000 %/W was achieved in a single-pass configuration.

The surface enhanced second harmonic generation of light from a randomly rough metal surface in the Kretschmann geometry

We present results of perturbative calculations of the second harmonic light generated in the transmission of p-polarized light through a thin metal film with a one-dimensional random surface in the Kretschmann attenuated total reflection (ATR) geometry. The metal film is deposited on the planar surface of a prism through which the light is incident. The back surface of the film is a one-dimensional random surface whose generators are perpendicular to the plane of incidence. It is in contact either with a semi-infinite vacuum or with a semi-infinite nonlinear crystal (quartz). It is shown that when the random surface separates the metal film from vacuum so that the nonlinearity of the film surfaces gives rise to the harmonic light, for a general angle of incidence a dip appears in the angular dependence of the intensity of the transmitted harmonic light in the direction normal to the mean surface. When the second harmonic generation is due to the nonlinearity of the crystal in contact with the metal film, a peak in the angular dependence of the intensity of the transmitted harmonic light occurs in this direction. These dips and peaks are multiple-scattering effects. However, when the angle of incidence is optimal for the excitation of surface plasmon polaritons at the film-vacuum/nonlinear crystal interface the nonlinear mixing of the incident light and the backward propagating surface plasmon polariton leads to an intense peak in the angular dependence of the intensity of the transmitted harmonic light in the direction normal to the mean surface. This peak is already present in the single-scattering approximation.

Effect of Edge Plasmon Excitation at Metal Grating on the Second Harmonic Generation of Light

The enhancement of the second harmonic generation (SHG) of light due to edge plasmon excitation on a metal grating is studied. Optimal conditions for edge plasmon excitation by laser radiation are evaluated. The role of surface and edge plasmons on the enhancement of SHG is considered.