Sellmeier and thermo-optic dispersion formulas for KTP

KTP has been found to be phase matchable for type-2 second-harmonic generation of the third harmonics of the CO2 laser wavelengths at 9.2714 and 9.5525 microm at 20.0 degrees C. The resulting angle and temperature-tuning data combined with the literature values of the Nd:YAG laser-pumped optical parametric oscillator were used to improve the Sellmeier equations and the thermo-optic dispersion formula that reproduce well the temperature-tuned 90 degree phase-matching conditions of the flux-grown crystals. Applications to quasi phase matching are presented.     

Design rules for phase-matched terahertz surface electromagnetic wave generation by optical rectification in a nonlinear planar waveguide

The theory of guided waves in metal-dielectric planar multilayer structures is applied to reduce the loss and maximize optical nonlinearity for efficient terahertz-field generation in a surface electromagnetic wave by femtosecond laser pulses confined in a (chi)((2)) nonlinear planar waveguide. For typical parameters of thin-film polymer waveguides and metal-dielectric interfaces, the optimal size of the (chi)((2)) waveguide core providing the maximum efficiency of terahertz plasmon-field generation is shown to be less than the wavelength of the optical pump field.     

Sellmeier Coefficients for the Birefringence and Refractive Indices of ZnGeP(2) Nonlinear Crystal at Different Temperatures

Birefringence (B(f)), refractive indices, and their temperature derivatives (dB(f)/dT) determine the temperature characteristics of nonlinear-optical laser devices. The birefringences at different temperatures are analyzed critically by use of a new physically meaningful Sellmeier equation for what is to the author's knowledge the first time the birefringences at different operating temperature from 14 to 500 K and wavelength for ZnGeP(2) nonlinear crystal have been found. This equation is based on the average electronic absorption gap in the UV region and the lattice absorption gap at the IR region. In this model the fitting accuracy is better than the experimental accuracy of ?0.0001 at different temperatures. The refractive indices are estimated at different temperatures from the room-temperature values, the thermo-optic coefficients, and the smoothed values of birefringence. The Sellmeier coefficients for refractive indices that are used to characterize the currently available nonlinear-optical devices satisfactorily are then evaluated. These optical constants are essential in characterizing the parametric short-pulse generation in the mid-IR region.     

Second-harmonic and sum-frequency generation in ZnGeP(2)

ZnGeP(2) has been found to be phase matchable for type-1 second-harmonic generation of a CO(2) laser to as high as 10.78 mum at 20.0 degrees C. The Sellmeier equations and nonlinear optical constant of this crystal are reported.     

Sellmeier coefficients and dispersion of thermo-optic coefficients for some optical glasses

The refractive index and its variation with temperature, the thermo-optic coefficient (d n/dT), are analyzed with two separate physically meaningful models for more than a dozen of some important Schott and Ohara optical glasses to find the refractive index at any operating temperature for any wavelength throughout the transmission region. The room-temperature catalog values of refractive indices are fitted with a two-pole Sellmeier equation. Both the average electronic absorption band gap and the lattice absorption frequency, lying in the vacuum UV and IR regions, respectively, contribute to the refractive indices and their dispersion. The estimated absorption band gaps are at 8.5-11.9 eV, and these values agree with the measured values at 8.8-11.6 eV satisfactorily for normal optical glasses. The higher-index glasses have electronic absorption in the region of 5.6-6.3 eV, and the estimated band gap of SF6 glass is 6.0 eV. The dispersion of thermo-optic coefficients is accounted for satisfactorily with a model, based on three physical parameters, the thermal expansion coefficient and excitonic and isentropic optical band gaps that are in the vacuum UV region. These optical constants are used to compute refractive indices at any operating temperature and wavelength. The Abbé number and the chromatic dispersion characteristics of these glasses are evaluated from the computed optical constants; the values of the chromatic dispersions are evaluated particularly at the three optical windows of the optical fiber communication systems and femtosecond technology.     

Sellmeier and thermo-optic dispersion formulas for RbTiOPO4

The thermo-optic constants for RbTiOPO₄ were measured from 20.0 to 120.0 °C in the 0.532–1.571 μm range. The Sellmeier and thermo-optic dispersion formulas that reproduce well the temperature-dependent phase-matching conditions for the normal and periodically poled crystals are presented.     

Two-temperature synthesis of ZnGeP2

We describe a modified two-temperature process for reproducible high-volume (up to 500 g) synthesis of the nonlinear-optical semiconductor ZnGeP₂, which enables the preparation of nominally stoichiometric material. The major reaction intermediates in the two-temperature ZnGeP₂ synthesis are ZnP₂, Zn₃P₂, GeP, and Ge. Using x-ray diffraction, we refined the interplanar spacings in the tetragonal structure of ZnGeP₂ and fcc structure of GeP and indexed peaks missing in the PDF cards 33-1471 (ZnGeP₂) and 21-353 (GeP).     

Photorefractive effect in ZnGeP2 single crystal

The photorefractive effect in a diamondlike single crystal of ZnGeP₂ has been studied for the first time. This phenomenon can be used for holographic data recording in ZnGeP₂ crystals. Two-wave mixing in the bulk of ZnGeP₂ has been studied. The diffusion length of photogenerated charge carriers, the Maxwell relaxation time, and the product μτ of the charge carrier mobility and lifetime have been determined.     

ZnGeP2晶体点缺陷的研究进展

ZnGeP2晶体是具有重要应用背景的红外非线性光学材料.晶体中的点缺陷严重限制了ZnGeP2晶体的应用发展.本工作介绍了ZnGeP2晶体点缺陷的最新研究进展情况.首先,利用电子顺磁共振技术研究了ZnGeP2晶体的点缺陷.主要存在缺陷是受主缺陷V-Zn及施主缺陷VOP和Ge Zn,其相应的缺陷能级分别为E(V-Zn)=EC-(1.024±0.03)eV,E(VOP)=EV (1.61±0.06)eV和E(Ge Zn)=EV (1.70±0.03)eV.对晶体作了电子照射及高温退火等处理后,又分别发现了两种缺陷V3-Ge和Vpi.其次,利用全势能线性muffin-tin轨道组合法模拟研究了ZnGeP2晶体的点缺陷.主要存在缺陷及缺陷能级的计算结果与实验结果基本一致,但由于理论模拟与实际情况还存在差距,有些计算结果与实验结果相矛盾.因此,将实验与理论有机结合研究晶体的点缺陷是今后研究的重点.     

Few-cycle terahertz generation and spectroscopy of nanostructures

We report on new schemes for terahertz (THz) generation. The THz efficiency of photoconducting antennas can be increased by using a cavity effect for the near-infrared pump beam. The cavity is formed by a molecular beam epitaxy grown semiconductor Bragg mirror below the photoconducting layer. The optical confinement is accompanied by an electrical confinement suppressing undesired leakage currents and providing a constant electric field in the active layers. The performance of this cavity-enhanced emitter is further improved by using a mobility optimized low-temperature GaAs layer. This emitter is successfully used in a femtosecond Ti:sapphire laser cavity for highly efficient intracavity THz generation, where the photoconductive layer serves also as a saturable absorber. The broadband THz pulses generated are used for time-resolved spectroscopy of nanostructures. We study the dynamics of intersubband transitions in semiconductor quantum wells. The relaxation of carriers excited by a near-infrared pump pulse is investigated by measuring the THz absorption between the different subbands with our THz pulses. For transition energies below the optical phonon energy we find relatively long relaxation times with a strong dependence on the excited carrier density.     

Theoretical analysis of phase-matched second-harmonic generation and optical parametric oscillation in birefringent semiconductor waveguides

We analyze the phase-matching conditions for second-harmonic generation (SHG) and optical parametric oscillation (OPO) in birefringent nonlinear semiconductor waveguides and apply these results to the model system of ZnGeP(2) on a GaP substrate. The analyses and numerical results show that phase matching can be achieved for OPO and SHG for reasonable guide thicknesses throughout much of the infrared, indicating significant potential applications for nonlinear birefringent waveguides. For the fundamental mode of a relatively thick guide the region of phase matching and the phase-matching angles are similar to those in bulk material. However, the waveguide has the added flexibility that phase-matched coupling can occur between the various modes of the guide. For example, the phase-matching region for SHG can be considerably extended by coupling the pump into the guide in the fundamental, m =, mode and phase matching to the m = mode of the second harmonic. Significantly, the results indicate, among other things, that ZnGeP(2) waveguides with harmonic output in the m = mode can be used for efficient SHG from input radiation in the 9.6-10.6-mum region where bulk efficiencies in this wavelength range are too small to be useful.     

Transient thermal lens in a ZnGeP(2) crystal

The first observations, to the authors' knowledge, of transient thermal lensing in a ZnGeP(2) crystal achieved with 2.09-μm laser excitation of 800-μs, 70-mJ pulses at 30 Hz and by burst-mode Q-switched pumping are presented. The laser power transmitted through an aperture was approximated by an adiabatic model with currently accepted values for the thermal properties of ZnGeP(2) and corresponded to focal-length changes from infinity to 10 cm during each 800-μs pulse. Similar results were seen when the crystal was operated as an optical parametric oscillator. This transient thermal lens severely limits ZnGeP(2) as a material for use in optical parametric oscillators for these modulated, high-power operating conditions.     

ZnGeP2 heterocontact with layered III–VI semiconductors

The photoelectric properties of heterojunctions fabricated by clamping wafers of ternary p-ZnGeP₂ and InSe and GaSe layered semiconductors onto an optical contact have been studied for the first time and results are reported. The photosensitivity in these structures is greatest when they are illuminated from the side with the ZnGeP₂ wafer, and reaches 150 V/W at T=300 K. In InSe/ZnGeP₂ heterostructures, a window effect is observed in the range 1.2–2 eV, whereas for GaSe/ZnGeP₂ structures, the photovoltaic effect has a maximum near 2 eV because of the proximity of the band gaps in the contacting semiconductors. Pis’ma Zh. Tekh. Fiz. 23, 1–5 (June 12, 1997)     

水平温梯冷凝法生长ZnGeP_2单晶

采用高纯(6mol/L)Ge、Zn、P单质为原料,按化学计量比并富P 0.2%配料,通过双温区法合成ZnGeP2多晶粉料,再用水平温梯冷凝法(HGF)生长出尺寸达10mm×20mm×80mm的单晶棒。对单晶进行了X射线衍射、红外透过率、热导率等测试,测试结果表明;单晶完整性好,红外透过率较高;5mm厚晶片(未退火、镀膜)在2～8μm范围内平均透过率可达54%以上;在室温附近(297.34K)热导率为35.89W/(m.K)。     

ZnGeP2多晶料合成与晶体生长

以99.999%的锌、锗和红磷为原料通过直接化合的方法合成ZnGeP2多晶料,采用布里奇曼法通过自发成核方式生长出尺寸为Ф7mm×25mm的ZnGeP2晶体.X射线粉末衍射实验表明合成的多晶料的成分是ZnGeP2,所获ZnGeP2晶体的结构属于四方晶系,空间群I42d.X射线摇摆曲线表明所得晶体完整性较好.用莫氏硬度计测得ZnGeP2晶体的莫氏硬度为6.5.测量了晶体的热重和差热曲线,证明在室温～800℃的范围内晶体热学性质稳定.     

Magnetic Resonance in ZnGeP2 and (Zn,Mn)GeP2

Electron paramagnetic (EPR) and ferromagnetic resonance (FMR) have been studied in the system of (Zn,Mn)GeP₂ ferromagnetic layer grown on undoped ZnGeP₂ single crystal. Strong FMR signals are registered in the wide temperature range up to room temperature. EPR and photo-EPR of intrinsic defects are observed in ZnGeP₂ substrate. EPR spectra characteristic of Mn²⁺ ions on Zn²⁺ sites in the bulk appear after the growth of the ferromagnetic layer on ZnGeP₂ crystal indicating the efficient Mn-diffusion into the bulk crystal by the annealing treatments.