Phase-matching Angle Research Articles

Enhancement of surface plasmon polariton on graphene excited by four-wave mixing

We present a theoretical description of surface plasmon polariton (SPP) on a graphene surface excitated by four-wave mixing using two laser beams. The phase-matched incident angles of the two beams that meet the SPP excitation conditions are calculated, and the discussion of the generated SPP power dependence on the incident angles is presented. We demonstrate that there is an enhancement in the peak power at the optimum angles at 633 nm and 921 nm, which is about 30 and 850 times larger than the corresponding peak power on a gold surface, respectively.

Measurement of thermal refractive index coefficients of nonlinear optical crystal RbBe2BO3F2

The principal refractive indices of RbBe2BO3F2 (RBBF) crystal at wavelengths of 0.194, 0.254, 0.363, 0.405, 0.435, 0.546, 0.644, 0.706, and 1.014μm are accurately measured by using the vertical incidence method within the temperature range from 24 to 160°C. Equations of thermal refractive index coefficients as a function of wavelength that could be used to calculate the principal thermal refractive indices at different wavelengths are derived. Moreover, experimental phase-matching angles for second harmonic generation of RBBF at 266nm wavelength at different temperatures as well as the theoretical values built on our experiment results are also given.

Nonlinear Optical Properties of the AgGa<sub>1-x</sub>In<sub>x</sub>Se<sub>2</sub> Crystal

The nonlinear optical properties of a novel AgGa1-xInxSe2 crystal were investigated. Its absorption coefficients and band gap were determined at wavelength 0.8-19 μm. The coefficients of its Sellmeier dispersion equations were calculated by using linear interpolation based on the Sellmeier equations of pure AgGaSe2 and AgInSe2. The corresponding phase matching curves for the second harmonic generation (SHG) of CO2 laser radiation were calculated and plotted. The walk-off angle and accept angle curves were also determined and plotted. The measured phase matching angle θm and acceptance angle δθ·L are 68.5° and 3.66°·cm respectively for sample AgGa1-xInxSe2 (x=0.2).

Temperature-dependent Sellmeier equations of nonlinear optical crystal La_2CaB_10O_19

The thermal dependence principal refractive indices ofLa(2)CaB(10)O(19) (LCB) crystal at wavelengths of 0.254, 0.365, 0.405, 0.480, 0.546, 0.644, 0.852, 1.014, and 2.325 μm were accurately measured by using the vertical incidence method within the temperature range from 25 to 170 °C. We derived equations of thermal refractive index coefficients as a function of wavelength that could be used to calculate the principal thermal refractive indices at different wavelengths. The temperature-dependent Sellmeier equations were also derived and used to calculate the phase-matching angles for the third-harmonic generation of LCB crystal at different temperatures. Theoretical and experimental phase-matching angles for the type I third-harmonic generation of LCB crystal at different temperatures were in good agreement.

Linear and nonlinear optical properties of Na3La2(BO3)3 crystal

A 30×20×8 mm 3 Na 3 La 2 (BO 3 ) 3 crystal has been grown by the top-seeded solution growth method (TSSG) using Na 2 O–B 2 O 3 –NaF as flux. The refractive indices at thirteen wavelengths from 0.2537 to 2.325 μm were accurately measured by the minimum deviation method, and the Sellmeier equations were accordingly constructed. The nonlinear optical (NLO) coefficients were measured by the Maker fringe method, which gave results of d 31 =1.45 pm/V, d 32 =0.67 pm/V, and d 33 =−1.06 pm/V, respectively. For second-harmonic generation (SHG) of 1064 nm, the effective NLO coefficient ( d eff ) of type I phase-matching reaches the maximum value (1.44 pm/V) at the phase-matching angles θ =77.0°, ϕ =212.1°, which is larger than that of LiB 3 O 5 (LBO). First-principle calculations suggest that Na 3 La 2 (BO 3 ) 3 possesses two types of NLO-active atom groups, BO 3 group with π-orbital system and La-centered polyhedron with large polar displacement, of which the latter could be considered as a new type of NLO-active atom group. • The refrative index and NLO coefficient have been measured for the first time. • The maxium effective NLO coefficient is larger than that of LBO crystal. • The distorted rare earth cation-centered polyhedron is suggested as new NLO-active atom group.

Electrical and nonlinear optical studies of flux grown Mo and Fe doped KTP crystals

The molybdenum (Mo) and ferric (Fe) doped potassium titanyl phosphate (KTP) crystals were grown by high temperature solution growth (HTSG) technique. The concentration of Mo and Fe in grown crystals was measured by EDX analysis. The SHG efficiencies of the Mo and Fe doped KTP crystals were measured and it was found to be 1.77 and 1.38 times respectively higher than that of pure KTP crystal. The frequency dependence of dielectric constant, loss and ac conductivity was studied at room temperature. The phase matching measurements were made using a Q-switched Nd:YAG laser operating at 1064nm and the measured phase matching angles are 44.2° and 87.88° for Mo and Fe doped KTP crystals respectively.

A high energy 3.75 μm KTA optical parametric oscillator at a critical angle

A high energy 3.75 μm nano-second KTiOAsO4 (KTA) optical parametric oscillator (OPO) at a critical angle is demonstrated in this letter. The OPO is pumped by a 1.064 μm laser and the KTA crystal is cut at 41.2° in the XZ plane. The phase matching angle is at the edge of the phase match curve and the edge of the absorption region for mid-infrared lasers. The cavity is a signal resonant oscillator. The spatial distribution of the pump light is a quasi-plane wave and the pulse width is 10 ns. A 218 mJ signal at 1.484 μm and a 60 mJ idler at 3.75 μm are achieved with a pump energy of 795 mJ, corresponding to a conversion efficiency of 35%. The idler pulse width is 7 ns. The divergence angle in the walk-off plane is 4 mrad and it is 14 mrad in the other plane. The results prove that the OPO phase matching of KTA exists at 3.75 μm and the KTA OPO can generate a high energy idler at 3.75 μm.

High-power tunable terahertz generation from a surface-emitted THz-wave parametric oscillator based on two MgO:LiNbO3 crystals

A high-powered tunable terahertz wave (THz-wave) has been parametrically generated via a surface-emitted THz-wave parametric oscillator (TPO) pumped by a multi-longitudinal-mode Q-switched Nd:YAG laser. The effective parametric gain length was enlarged by employing two MgO:LiNbO3 crystals. The tunable THz-wave radiation from 0.8 to 2.8THz was realized via varying phase-matching angle between the pump wave and the Stokes wave. The maximum THz-wave radiation was 173.9nJ/pulse at 1.7THz as the pump energy was 82mJ, corresponding to an energy conversion efficiency of about 2.12×10−6 and a photon conversion efficiency of about 0.035%. The first-order, the second-order and the third-order Stokes waves were observed during the experiments.

Thermal refractive index coefficients of nonlinear optical crystal CsB_3O_5

The principal refractive indices of crystal CsB3O5 (CBO) at the wavelengths of 0.266, 0.355, 0.532, 0.473, 0.633, 1.064, and 1.338 μm are accurately measured by using the autocollimation method within the temperature range from 40°C to 190°C. We derive and report equations of thermal refractive index coefficients as a function of wavelength that could be used to calculate the principal thermal refractive indices at different wavelengths. Sellmeier equations at different temperatures were derived and used to calculate the phase-matching angles for the third-harmonic generation and the fourth-harmonic generation of CBO crystal at different temperatures.

Growth, thermal and spectral properties of Nd3+:YCa9(VO4)7 crystal

A new crystal of Nd3+:YCa9(VO4)7 was grown successfully by the Czochralski method. Its intensity of second harmonic generation is about 1.5 times as large as that of KH2PO4 crystal. The thermal physical properties and the spectral properties of the crystal were investigated in detail. Based on the Judd–Ofelt theory, the intensity parameters were obtained. From the measured principal refractive indices, the Sellmeir equations and the theoretical phase-matching angles of the crystal were obtained. The results showed that Nd3+:YCa9(VO4)7 crystal is expected to be a new self-frequency-doubling laser crystal.

Experimental Study of Nd:YVO<sub>4</sub>/KTP Solid Laser Pumped by Diode Laser

Build a diode laser end-pumped Nd:YVO4/KTP solid laser system, Nd:YVO4 crystal was used as the solid laser medium, it emitting 1064nm infrad laser when it was pumped by 808nm diode laser, then the 1064nm infrad laser was changed to 532nm green laser by frequency doubling with a KTP crystal inside the optical cavity. Based on experiment, the relationship between diode laser power output and diode laser injection current, the relationship between laser pump power and 532nm green laser output, and the other factors possibly affecting 532nm laser output which include KTP phase match angle, pump light focus position and all-solid-state-laser (ASSL) cavity length was also studied. The experimental results show that to increase the output of 532nm green light needs to improve the pump diode laser power, shorten the length of the solid laser cavity , focus the pump laser to the middle of the Nd:YVO4 crystal, and choose correct KTP crystal phase-matching angle.

CALCULATION OF EFFECTIVE NONLINEAR COEFFICIENT IN BIBO FOR SPONTANEOUS PARAMETRIC DOWN CONVERSION

We theoretically investigate the effective nonlinear coefficient d eff of spontaneous parametric down-conversion (SPDC) process in biaxial nonlinear crystal BiB3O6 (BIBO). We solve the Fresnel equations in the collinear degenerate down-converted configuration, and get the relations of phase-matching angles. Considering the double phase-matching, we compute the phase-matching angles with different wavelength. Furthermore, we simplify the expression of effective nonlinear coefficient out of the principal planes, and numerically calculate it varying with the angle and wavelength. These results indicate that there are three effective phase-matching schemes for SPDC which can be used to construct a system to generate entangled photon pairs.

Frequency Tuning Characteristics of a THz-wave Parametric Oscillator

Frequency tuning characteristics of a THz-wave by varying phase-matching angle and pump wavelength in a noncollinear phase-matching THz-wave parametric oscillator (TPO) are analyzed. A novel scheme to realize the tuning of a THz-wave by moving the cavity mirror forwards and backwards is proposed in a noncollinear phase-matching TPO. The parametric gain coefficients of the THz-wave in a <TEX>$LiNbO_3$</TEX> crystal are explored under different working temperatures. The relationship between the poling period of periodically poled <TEX>$LiNbO_3$</TEX> (PPLN) and the THz-wave frequency under the condition of a quasi-phase-matching configuration is deduced. Such analyses have an impact on the experiments of the TPO.

Realisation of four-wave mixing phase matching for frequency components at intracavity stimulated Raman scattering in a calcite crystal

The possibilities of implementing four-wave mixing (FWM) phase matching at stimulated Raman scattering (SRS) in a birefringent SRS-active crystal placed in a cavity with highly reflecting mirrors have been theoretically and experimentally investigated. Phase-matching angles providing conditions for five types of phase matching are determined for a calcite crystal. These types are characterised by different combinations of polarisation directions for the interacting waves and ensure FWM generation of either an anti-Stokes wave or the second Stokes SRS component. In agreement with the calculation results, low-threshold generation of the second Stokes SRS component with a wavelength was observed at angles of incidence on a calcite crystal of and , under SRS pumping at a wavelength of . This generation is due to the FWM coupling of the first and second Stokes SRS components with the SRS-pump wave.

Refractive indices, phase-matching directions and third order nonlinear coefficients of rutile TiO_2 from third harmonic generation

Experiments of third harmonic generation in rutile TiO2 allowed us to determine the phase-matching angles and the refractive indices of the crystal up to 4500 nm. We also showed that χ16 and χ18 coefficients of the third order electric susceptibility tensor exhibit opposite signs, and that |χ18(616.7nm)| = 9.7 × 10−20 m2V−2.

Investigation on second and third order nonlinear optical, phase matching and birefringence properties of γ-glycine single crystals

Optical quality γ-glycine single crystal of dimension 9×9×8mm3 has been grown by slow cooling method in the presence of lithium nitrate. The third order nonlinear refractive index and nonlinear absorption coefficient of the grown crystal were measured by Z-scan studies. The dispersion of birefringence behaviour was studied by modified channelled spectrum method. The relative second harmonic generation efficiency of grown crystal was measured by Kurtz and Perry technique and phase matching angle was also measured using Nd:YAG laser.

Investigation of operational characteristics of terahertz-wave parametric oscillators pumped by picosecond based on MgO:LiNbO3 crystal

Based on the technology of the non-collinear phase-matching about three-wave interaction in uniaxial crystal, the performance of nonlinear crystal MgO:LiNbO3(MgO:LN) including the phase-matching angles, effective nonlinear coefficient and THz-wave gain as well as its absorption coefficients are theoretically discussed under e-ee type phase-matching condition. And an external cavity is developed for terahertz-wave parametric oscillators pumped by picosecond laser (ps-TPOs). For optimizing the ps-TPOs performance, the focusing spot size in MgO:LN crystal, the geometric size of the MgO:LN crystal, the conversion efficiencies, and the stability of the THz-wave generation are designed and calculated. The calculated results provide a comprehensive theoretical basis for the ps-TPOs using difference-frequency generation (DFG) method and optimal performance to generate widely tunable terahertz waves in MgO:LN crystal.

Compensation for the thermal effect in the second-harmonic generation of a Q-switched nanosecond-kilohertz Nd:YVO4 laser

We report the quantitative relationship between the phase-matching condition and the surrounding temperature in a critical phase-matching second-harmonic generation of a Q-switched Nd:YVO4 laser with a high repetition rate. The thermal effect can be effectively compensated for by appropriately changing the phase-matching angle with respect to the surrounding temperature of a nonlinear optical crystal. A stable wavelength conversion from the 1064 nm fundamental to the 532 nm second harmonic in a type-I critical phase-matching lithium triborate crystal is experimentally achieved and the corresponding conversion efficiency up to 70% is obtained.

Amplification of fluorescence using collinear picosecond optical parametric amplification at degeneracy

We demonstrate the output characteristic of broadband parametric amplification of incoherent light pulses in a 355-nm pumped degenerate picosecond optical parametric amplification with either saturated or unsaturated amplification. The optical parametric amplifier is seeded by the fluorescence generated in a solution of pyridine-1 dye in ethanol. With the saturated amplification, we can obtain high energy incoherent light pulses, whose full width at half maximum bandwidth varies from 16 nm to 53 nm for the different phase matching angles near degeneracy. Moreover, the unsaturated bandwidth of the amplified pulses fits well to the calculated result at degeneracy. Selecting s-polarized fluorescence with a Glan—Taylor prism, the maximum bandwidth of the amplified fluorescence is found to be 59 nm for a purely s-polarized seed. The maximum output energy is 0.67 mJ for the optical parametric amplifier. By using an optical filter and compressor, the generated high energy incoherent light has great potential as the incoherent pump, signal or idler wave of a parametric down-conversion process, so that a wave with a high degree of coherence can be generated from an incoherent pump light.

Optical properties of Sr3NbGa3Si2O14 crystal

Single crystal of Sr3NbGa3Si2O14 was successfully grown using the conventional Czochralski technique. UV–VIS–NIR spectrometry and spectroscopic ellipsometry have been used to study the optical properties of SNGS crystal. From the transmission spectrum, the cut-off wavelength is determined to be 284nm. Refractive indices of SNGS crystal were accurately determined in the wavelength region between 350nm and 800nm, based on the analysis of the transmission spectrum and SE measurements at multiple angles of incidence. The effects of varied values of k on no and ne were also discussed. Furthermore, the phase matching angle of SNGS crystal is 39.00°.