Third Harmonic Research Articles

Direct third harmonic generation due to quadratic cascaded processes in periodically poled crystals

We report the first, according to our knowledge, experiment for direct third harmonic (TH) generation in periodically poled quadratic crystals. TH radiation of a diode array pumped and acousto-optically Q-switched Nd:YVO 4 laser is generated in a 25 mm long periodically poled lithium niobate (PPLN) crystal of period 7.0 μm. A theoretical model is developed that explains the experimental results. It predicts that the efficient phase-matched direct TH generation in periodically poled structures with duty factor 0.5 requires even order quasi-phase matching. In contrast to the similar experiments in bulk birefringence crystals, where direct phase matched TH signal is the sum of the contribution of both intrinsic and cascaded cubic nonlinearities, in periodically poled quadratic crystals only cascaded cubic nonlinearity contributes to the direct phase-matched TH signal.

Gap solitons in a medium with third-harmonic generation

We find two-component optical solitons in a nonlinear waveguide with a Bragg grating, including Kerr effects and third-harmonic generation (THG). The model may be realized in temporal and in spatial domains. Two species of fundamental gap solitons (GSs) are found. The first ("THG-gap soliton") has the bulk of its energy at the fundamental frequency (FF) and a lesser part in the third-harmonic (TH) band. The FF part of the soliton is always single humped; the TH part may be single or double humped. Stability domains for quiescent and moving THG-gap solitons strongly shrink with increase of velocity. The second species is the usual ("simple") GS, sitting entirely in the TH band. More complex solutions are also found, in the form of a bound state of a THG-gap soliton and two simple GSs, with a finite binding energy. When a THG-gap soliton is unstable, the instability is oscillatory. It may ultimately cause the THG-gap soliton to throw off some radiation and evolve into a localized structure with the FF and TH components out of phase, with or without internal oscillations. Stable solitons feature an excited state (i.e., they support a localized eigenmode).

Enhanced third harmonic reflection and diffraction in Silicon on Insulator photonic waveguides

Enhanced third harmonic (TH) generation from Silicon-On-Insulator (SOI) planar waveguides as well as SOI photonic crystal (PhC) slabs is studied in different angular configurations, both in the visible and infrared energy ranges. In the SOI planar waveguide, the multilayer structure causes the optical properties such as TH reflection to be different from those of bulk silicon samples. This behavior is well reproduced by calculations of TH reflectance.

Optical manipulation of third-harmonic generation via either one- or two-photon excitation in diarylethene-polymethylmethacrylate polymer thin films

Optical manipulation of third harmonic (TH) generation in diarylethene-polymethylmethacrylate (DE-PMMA) polymer thin films is obtained by either one- or two-photon excitation. TH intensity generated from a DE-PMMA polymer thin film decreases, when it is pumped by either 325 nm or 442 nm laser irradiation, which changes the molecular structure of DE molecules from an open-form (A form) to a closed-form (B form). TH intensity recovers to its original intensity level when all B form DE molecules return to an A form after being induced by either 532 nm or 1064 nm laser irradiation. The experimental results reveal that the second-order hyperpolarizability (γ) of the A form molecules may be larger than that of the B form molecules. Moreover, TH output efficiency is independent of the angle between the pump and probe polarization directions. This result is attributed to the two-dimensional structure of DE molecules.

Supercontinuum emission and enhanced self-guiding of infrared femtosecond filaments sustained by third-harmonic generation in air

The long-range propagation of two-colored femtosecond filaments produced by an infrared (IR) ultrashort pulse exciting third harmonics (TH) in the atmosphere is investigated, both theoretically and experimentally. First, it is shown that the coupling between the pump and TH components is responsible for a wide spectral broadening, extending from ultraviolet (UV) wavelengths (220 nm) to the mid-IR (4.5 microm). Supercontinuum generation takes place continuously as the laser beam propagates, while TH emission occurs with a conversion efficiency as high as 0.5%. Second, the TH pulse is proven to stabilize the IR filament like a saturable quintic nonlinearity through four-wave mixing and cross-phase modulation. Third, the filamentation is accompanied by a conical emission of the beam, which becomes enlarged at UV wavelengths. These properties are revealed by numerical simulations and direct experimental observations performed from the Teramobile laser facility.

Magnetization-induced second- and third-harmonic generation in transparent magnetic films

We describe the magnetization-induced second-harmonic (SH) generation in (Fe^II_xCr^II_1−x)_1.5[Cr^III(CN)_6]⋅7.5H2O and the magnetization-induced third-harmonic (TH) generation in Y1.5Bi1.5Fe3.8Al1.2O12 (Bi,Al:YIG). The polarization plane of a SH wave from a (Fe^II_xCr^II_1−x)1.5[Cr^III(CN)6]⋅7.5H2O film was rotated by an applied external magnetic field. This SH rotation is ascribed to the interaction between the electric polarization along the out-of-plane and spontaneous magnetizations. In particular, the magnetic linear term chi_ijkL magn(1) contributed to the SH rotation. Applying a longitudinal external magnetic field to a Bi,Al:YIG magnetic film rotated the polarization plane of the TH wave. This TH rotation is understood by the contribution of the magnetic term of chi_yxxxZ magn(1) in a third-order nonlinear optical susceptibility.

Numerical simulation of cascaded third harmonic generation for both phase matched and mismatched schemes

Numerical solutions to the nonlinear coupling-wave equations of second harmonic (SH) and third harmonic (TH) generators are investigated for both phase matched and phase mismatched configurations. For phase mismatched TH generation, several kinds of schemes (the phase mismatch either in second harmonic generation (SHG) or sum-frequency generation (SFG) process) are considered and analyzed. The physical nature corresponding to the different ratios of the coupling coefficients is discussed.

Magnetization-induced third harmonic generation in magnetic nanogranular films: Correlation with giant magnetoresistance

Magnetization-induced third harmonic (TH) generation was observed in magnetic nanostructures—nanogranular CoxAg1− x films—possessing giant magnetoresistance (GMR). The magnetization-induced contribution to the TH intensity was studied as a function of the concentration of a magnetic component (cobalt) in the films. Magnetic contrast of the TH intensity was found to correlate with the GMR coefficient: both parameters simultaneously reach extremum in the range of cobalt concentrations x∼0.3–0.35.

ポリエチレンテレフタレート基板上に作成されたバナジルフタロシアニン薄膜の３次非線形光学感受率

Vanadyl-phthalocyanine (VOPc) thin films were prepared by molecular beam epitaxy (MBE) on polyethylenetelephthalate (PET) film. The morphologies and nonlinear optical properties of VOPc thin films were investigated with UV/Vis spectra, AFM images and the incident angle dependence of second harmonic (SH) and third harmonic (TH) intensities measured by Marker fringe. The UV/Vis spectra of samples 1 to 4 have an absorption peak at 830 nm. Therefore, the phase morphology of samples 1 to 4 is Phase II. The third optical susceptibility (χ (3) ) estimated from the maximum TH intensity is 7.5 × 10-8 esu. From the χ (3) value obtained, the VOPc thin film fabricated on PET substrate can be applied in optical devices such as optical switching so on.

Self-frequency tripling from two cascaded second-order nonlinearities in GdAl3(BO3)4:Nd3+

We combine inside a single noncentrosymmetric laser crystal, GdAl3(BO3)4:Nd3+, a stimulated emission and two second-order nonlinearities in cascade. The first one self-doubles the 1062.8 nm Nd3+ laser emission corresponding to the F3/24→I11/24 channel, despite the fact that it is not phase-matched. The second one can be phase-matched or not and mixes the laser wave and its second harmonic (SH) in order to produce the third harmonic (TH) at 354.3 nm.

High-throughput characterization of linear and nonlinear optical properties in composition-spread (Sr,Ca) 2CuO 3 thin-films

We have constructed a high-throughput spectrometer and a nonlinear optical tester used for the characterization of combinatorial thin-film libraries. The optical spectrometer consists of a multi-channel detector and an automated bidimensional translation stage. The transmission spectrum of an area of 0.5 mm×2 mm can be measured for a wavelength range of 280–900 nm. Our nonlinear optical tester uses a compact mode-locked fiber-laser as an excitation source. The laser beam is focused by a graded index lens, the fundamental light is filtered out, and the third-harmonic (TH) light is detected by a photomultiplier. The data collection and the motion of the stepping motor-driven stage are synchronized. Typical measurement time for a composition-spread thin-film is 5 min. A demonstration is shown for a composition-spread thin-film of one-dimensional cuprate (Sr x Ca 1− x ) 2CuO 3 with gigantic third-order optical nonlinearity.

Theoretical investigations of efficient cascaded third-harmonic generation in quasi-phase-matched and -mismatched configurations

Theoretical and numerical solutions of the nonlinear coupling-wave equations of second-harmonic (SH) and third-harmonic (TH) converters are investigated for both phase-matched and phase-mismatched configurations. For phase-mismatched TH generation, several kinds of schemes [the phase mismatch in either SH generation or sum-frequency generation (SFG) as well as the phase mismatch in both SH generation and SFG] are considered and analyzed. The optimal TH converting properties for generalized phase-mismatching operation are discussed and studied. It is found that efficient TH generation depends not only on the magnitude of the coupling coefficients but also on their ratio. A 100% TH output can be obtained at a particular ratio. The physical nature of the different ratios of the coupling coefficients is discussed.

Nonlinear Optical Properties and Organic Gas Effects of VOPc Thick Films Prepared on KBr Substrate

Vanadyl-phthalocyanine (VOPc) thick films were prepared by an organic molecular beam deposition (OMBD) method on KBr substrate. The morphologies and nonlinear optical properties of VOPc films were investigated with VIS/UV spectra, the incident angle dependence of third harmonic (TH) intensity measured by Marker fringe, SEM, and AFM images. The morphology of VOPc thick film prepared at the substrate temperature of 200°C is a pseudoepitaxy. Cracks and wrinkly parts on the film surface are observed from SEM and AFM images. The VOPc thick film exposed for 25 and 50hrs to 1.8 atm organic gas changes from pseudoepitaxy to epitaxy. Cracks and wrinkly parts on the film surface disappear due to the molecular diffusion during the gas treatment. It depends upon time exposed in organic gas. A VOPc thick film treated for 75hrs in 1.8 atm organic gas almost perfectly changes from pseudoepitaxy to epitaxy because it is impregnated with organic gas.

１，２‐ジクロロエタンと四塩化炭素の有機ガスで処理されたバナジルフタロシアニン蒸着膜の結晶構造

Vanadyl-phthalocyanine (VOPc) thick films were prepared by a molecular beam epitaxy (MBE) on KBr substrate. The morphologies and nonlinear optical properties of VOPc thick films before and after organic gas treatment were investigated with Vis/UV spectra, the incident angle dependence of second harmonic (SH) and third harmonic (TH) intensity measured by Maker fringe. The Vis/UV spectrum of Sample 1 has an absorption peak at 780 nm. Therefore, the phase morphology of Sample 1 is a pseudoepitaxy. Sample 1 exposed for 25 hrs in 1.8 atm organic gas prepared with 1, 2 -dichloloethane changes from pseudoepitaxy to epitaxy. On the other hand, Sample 1 exposed in carbon tetrachloride gas does not change from pseudoepitaxy to epitaxy. These results were explained with the donor-acceptor interaction between a VOPc and carbon tetrachloride molecule.

New laser-induced fluorescence scheme for simultaneous OH and NO detection by a single laser set-up

In this communication, we propose a new laser-induced fluorescence (LIF) scheme that allows the simultaneous detection of OH and NO by a single laser set-up. OH is detected by the second harmonic (SH) of a dye laser tuned to the (0,0)-band of the 3064 A system, while its third harmonic (TH) is used to detect NO through excitation of the (2,0)-band of the γ system. This scheme is presented and discussed within the framework of its potential use in field instruments for the measurement of tropospheric OH concentration.

Nonlinear optical properties and morphologies of vanadyl‐phthalocyanine thin films prepared on polyethylene‐terephthalate film

AbstractVanadyl phthalocyanine (VOPc) crystal thin films were prepared on poly(ethylene terephthalate) (PET) film. The VOPc film prepared on PET substrate at 120 °C had Phase II. The third harmonic (TH) intensity of the VOPc film was measured by the marker fringe method. The third optical susceptibility (χ(3)) estimated from TH intensity is 3.5 × 10−9 esu. The transition from Phase I to Phase II of the VOPc film was enhanced with corona charging. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(2): 36–43, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10022

Reliability of thin-film resistors: impact of third harmonic screenings

Third harmonic (TH) testing is a probably underrated in-line screen tool to detect and eliminate potential infant mortality failures in passive components that is not in focus of current interest. The test is fairly rapid, convenient, and the associated equipment is relatively inexpensive. TH screening is thus advertised as a general means of ensuring robust behaviour of parts that pass this test. The author presents results of an evaluation of the present usage of this screen with a variety of thin-film resistors. A number of questions are considered: • How do resistor manufacturers use this screen and how do they establish accept/reject criteria and what are the conclusions of 20 years of experience with that method? • Are there known physical and chemical defects that this screen misses? • Can rejected parts be correlated with behaviour in short-term and long-term reliability tests? • Can new, small, surface mount technology resistors be reliably screened with TH testing and where are the limitations?

Crucial effects of coupling coefficients on quasi-phase-matched harmonic generation in an optical superlattice

Coupling of optical parametric processes in an optical superlattice through quadratic nonlinearity was analyzed theoretically. Solving the coupled equations, we found that efficient quasi-phase-matched third-harmonic (TH) generation depends not only on the magnitude of the coupling coefficients but also on their ratio. Theoretically, all the fundamental energy can be transferred to the TH at a particular ratio. In other cases, there exists an optimum condition that corresponds to a maximum TH conversion efficiency. The result is of practical importance for the design of TH devices.

Second-harmonic and third-harmonic generation in a three-component fibonacci optical superlattice

Harmonic generation in a three-component Fibonacci optical superlattice (3CFOS) is analysed theoretically. The Fourier spectrum of the structural function of the 3CFOS is numerically calculated. The positions of reciprocal vectors are in good agreement with the theoretical prediction. The intensities of the second harmonic (SH) and third-harmonic (TH) are calculated relative to the depletion of the fundamental. The dependence of the SH and TH intensity on structural parameters is discussed. Numerical calculation shows that, compared with two-component Fibonacci optical superlattice (2CFOS), there are more plentiful harmonic spectrum and adjustable structure parameters in 3CFOS. By chosen the reciprocal vectors and adjusted the structure parameters, the higher transform efficiency of THG is obtained.

Optical nutation under Raman excitation

Optical nutation under Raman excitation accompanied by considerable (up to inverted) population changes was observed. The Raman-active 6P1/2 -6P3/2 transition of thallium atoms was excited by picosecond pulses of a dye and an Nd : YAG laser. Transition polarization and upper level population were probed by delayed pulses at a fixed time by means of coherent Raman scattering and third harmonic generation schemes, respectively. Optical nutation manifested itself in corresponding changes of anti-Stokes and third harmonic signal energies as functions of the product of the pump pulses energies. As a result of the a.c. Stark shift, the nutation picture strongly depended on the sign of wavenumber detuning from the transition wavenumber. Copyright 2000 John Wiley & Sons, Ltd. cross-sections in comparison with those of rotational or rotation-vibrational transitions. For the relatively high transition wavenumbers, typical for atoms, the Doppler dephasing time T 2 can be as low as1 ns. The coher- ence of excitation is secured, provided that pump pulses shorter than T1, T2 and T 2 are applied. By varying the energy of the pump pulses, the system can be transfered into different states, including a state with inverted popu- lation. This scheme was discussed in Ref. 5, where it was proposed to monitor the transition polarization by measur- ing the energy of the coherent Raman scattering signal as function of the product of the pump pulses energies with the probe pulse delayed at a fixed time relative to the pump pulses. At the same time, the third harmonic (TH) is much more effectively generated in thallium, when the upper level 6P3=2 of the Raman-active transition is populated. 6 This effect can be used to monitor the population of the excited level. The application of picosecond pulses ensures, as a rule, the fulfillment of the coherent excitation conditions in gases. Since the Raman cross-sections are small, it is necessary to use powerful picosecond pulses to obtain suf- ficient population changes. This makes the manifestation of the a.c. Stark effect real. In the present work, the optical nutation at a Raman- active transition was observed at resonant Raman excita- tion by picosecond pulses. Optical nutation was accompa- nied by considerable population changes. The a.c. Stark shift manifested itself in an 'asymmetry' of the nutation picture relative to the sign of the wavenumber detuning .!1 !2/ !R.