Efficiency of laser initiation and absorption spectra of PETN

A comparative study of the efficiency of the laser initiation of PETN by the first and second harmonics (1060 and 530 nm) of a neodymium-doped phosphate glass laser was performed. A significant difference in the efficiency of PETN initiation by the different harmonics was revealed: as the initial temperature of the sample increased from 373 to 450 K, the threshold initiation fluence decreased from 3.0 to 0.5 J/cm²; at the same time, the second harmonic failed to initiate PETN even at a fluence of 10 J/cm². The absorption spectrum of PETN was found to have a weak absorption band with a maximum at λ _m = 1020 nm. It was assumed that the high efficiency of initiation by the first harmonic is associated with light absorption (photo-initiation) by this band     

Growth and characterization of new semi-organic l-proline strontium chloride monohydrate single crystals

The present communication deals with the synthesis, single crystal growth and characterization of a new nonlinear optical material l-proline strontium chloride monohydrate (l-PSCM). Single crystals have been grown using the slow solvent evaporation technique. Single crystal XRD analysis confirmed that the crystal belongs to the orthorhombic structure with lattice parameter a=6.6966(3) Å, b=12.4530(5) Å, c=15.2432(5) Å and space group P2₁2₁2₁. Presence of various functional groups in l-PSCM and protonation of the ions were confirmed by Fourier transform infrared spectroscopy (FT-IR) analysis. The melting point of the single crystal was found to be 126 °C using DSC. Ultraviolet-visible spectral analyses showed that the crystal has low UV cut-off at 226 nm combined with very good transparency of 90% in a wide range. The optical band gap was estimated to be 5.82 eV. Capacitance and dielectric-loss measurements were carried out at different temperatures in the frequency range 1 kHz-2 MHz. The dielectric constant and loss factor were found to be 21 and 0.03 at 1 kHz at room temperature, respectively. Microhardness mechanical studies show that hardness number (H_v) increases with load for l-PSCM single crystals the by Vickers microhardness method. Second harmonic generation (SHG) efficiency was found to be 0.078 times the value of KDP.     

飞秒BBO光参量放大中闲频光二次谐波的产生

由于相位匹配条件和非线性晶体透光范围的限制，400nm蓝光抽运的飞秒β-BaB₂O₄（BBO）光参量放大（OPA）输出的参量光调谐范围有限，很难得到波长小于460nm的蓝光和近紫外光.实验采用1kHz钛宝石九通啁啾脉冲放大器的倍频蓝光作抽运光，超连续白光 作种子光，在Ⅰ类非共线相位匹配条件下，利用宽带的飞秒BBO OPA，在一定的实验参数下 获得了530—810nm放大的信号光，以及810nm—17μm波段范围的闲频光.与此同时 ，还获得了410—700nm连续可调的闲频光的二次谐波，其与闲频光层叠分布，单脉冲能量 为26μJ，转换效率大于5%.仅利用单块晶体的飞秒BBO OPA就可以获得410—810nm连 续可调的飞秒脉冲输出，从而为更多研究和应用的需要提供了重要的光源.对飞秒光参量放 大中闲频光二次谐波产生的条件也进行了理论分析. 关键词： 二次谐波 闲频光 非共线相位匹配 飞秒光参量放大     

Photoinduced non-linear optical diagnostic of SiNxOy/Si111 interfaces

Anisotropic (elliptically polarized) photoinduced second harmonic generation (PISHG) in SiN_xO_y/Si1 1 1 films was proposed for contact-less monitoring of specimens with different nitrogen to oxygen (N/O) ratios. As a source for the photoinducing light, we used a nitrogen Q-switched pulse laser at wavelengths of 315, 337 and 354 nm as well as doubled frequency YAG–Nd laser wavelength (λ=530 nm). The YAG : Nd pulse laser (λ=1.06 μm; W=30 MW; τ=10–50 ps) was used to measure the PISHG. All measurements were done in a reflected light regime. We found that the output PISHG signal was sensitive to the N/O ratio and the film thickness. Measurements of the PISHG versus pumping wavelengths, powers, incident angles as well as independent measurements of the DC-electric field induced second harmonic generation indicate the major role played in this process by axially symmetric photoexcited electron–phonon states. The SiN_xO_y films were synthesized using a technique of chemical evaporation at low pressures. Films with thickness varying between 10 and 30 nm and with an N/O ratio between 0 and 1 were obtained. Electrostatic potential distribution at the Si1 1 1–SiN_xO_y interfaces was calculated. Comparison of the experimentally obtained and quantum chemically calculated PISHG data are presented. High sensitivity of anisotropic PISHG to the N/O ratio and film thickness is revealed. The role of the electron–phonon interactions in the dependencies observed is discussed. We have shown that the PISHG method has higher sensitivity than the traditional extended X-ray absorption fine structure spectroscopic and linear optical method for films with the N/O ratio higher than 0.50.     

Third harmonic generation of CO2 laser radiation in AgGaSe2 crystal

Generation of third harmonic of CO₂ laser radiation has been obtained in a type-II, ϑ=57° cut 9 mm thick AgGaSe₂ crystal for the first time by sum-frequency-mixing of the fundamental with its second harmonic, the latter being obtained using another type-I, ϑ=55° cut 11 mm thick AgGaSe₂ crystal. The energy conversion efficiencies obtained for second harmonic and third harmonic generations are 6.3% and 2.4% respectively with the input fundamental pump power density of 5.9 MW/cm² only. The wavelength of the fundamental CO₂ laser radiation used for the generation of harmonics is 10.6 μm, P(20) line. A compact TEA CO₂ laser source has been built in the laboratory.     

Optical,spectral and thermal properties of organic nonlinear optical single crystal: 2,3-Dimethoxy-10-oxostrychnidinium hydrogen oxalate dihydrate

The potential organic nonlinear optical single crystal of 2,3-dimethoxy-10-oxostrychnidinium hydrogen oxalate dihydrate has been grown by slow evaporation solution growth technique (SEST) using ethanol–water solution at room temperature. The powder X-ray diffraction study reveals that the crystal belongs to orthorhombic system with non-centrosymmetric space group P2₁2₁2₁ and the cell parameters are a = 7.61 Å, b = 10.73 Å, c = 29.49 Å, V = 2410.75 Å³. The functional groups of the synthesized compound have been identified by FT-Raman and FTIR analyses. Photoluminescence spectroscopy study is determined to explore its efficacy towards device fabrications. Birefringence measurement has been carried out in order to analyze the optical homogeneity of the grown crystal. The optical constants such as reflectance (R) and extinction coefficient (K) have been determined from the transmittance data. The relative second harmonic efficiency of the compound is found to be 4 times greater than that of KDP. DTA-DSC measurements indicate that the crystal is thermally stable up to 174 °C.     

Generation of amplitude squeezed green light from a high efficiency PPKTP frequency doubler

We report on a high-efficiency 532 nm green light conversion from an external cavity-enhanced second harmonic generation of a home-made 1064 nm single-frequency Nd:YVO₄ laser with a periodically poled KTP crystal. A stable green power of 60 mW with a conversion efficiency of 75% was measured. Meantime, we investigate the quadrature amplitude noise of the green light at the same experimental setup and 0.6 dB green light squeezing was experimentally observed (taking into account the total detection efficiency of 58%, the squeezing should be 1.1 dB). The squeezing as a function of input power was also studied and we found qualitative agreement with theoretical prediction.     

Studies on amino acid picrates: Crystal growth,structure and characterization of a new nonlinear optical material l-isoleucinium picrate

A series of l-amino acids, isoleucine, valine, glutamine, methionine, arginine, cystine and aspargine are employed to form picrates with picric acid (1:1). A comparison of cell parameters reveals that expected picrates are formed only in the case of l-valine and l-isoleucine. l-Isoleucinium picrate (LIP), a new nonlinear optical material was grown from aqueous medium by the slow evaporation of equimolar mixture of l-isoleucine and picric acid. The structure of the grown crystal as determined by single crystal XRD diffraction analysis reveals that it belongs to the monoclinic system with space group P2₁ and the cell parameter values are, a = 9.970(3) Å; b = 6.425(2) Å; c = 12.871(4) Å; β = 109.54(3)°; V = 770.0(4) Å³; Z = 2. The presence of functional groups in the LIP is confirmed by FT-IR vibrational patterns and the good crystallinity indicated by powder X-ray diffraction method. The relative second harmonic generation (SHG) efficiency measurements reveal that the LIP is a highly efficient nonlinear optical (NLO) material having an activity 16 times as that of the reference material potassium dihydrogen phosphate. The optical transparency has been studied using UV–vis spectrophotometer and the absorption is minimum in the visible region. Thermogravimetric and differential thermal analyses reveal the purity of the sample and no decomposition is observed up to the melting point.     

Studies on the optical and mechanical properties of organic nonlinear optical 1-(4-fluorostyryl)-4-nitrostilbene (FNS) single crystal

A new organic nonlinear optical material 1-(4-fluorostyryl)-4-nitrostilbene (FNS) has been synthesized and single crystals of FNS were grown using solvent evaporation solution growth technique (SESGT) by 2-butanon solvent. Single crystal x-ray diffraction analysis reveals the unit cell parameters of the grown crystal are a = 9.494(4) Å, b = 9.864(2) Å, c = 19.501(7) Å and it belongs to monoclinic system with noncentrosymmetric space group. Optical transmittance of the grown crystal has been studied by UV-Vis-NIR spectrum. The optical properties of FNS have been studied by means of optical transmittance measurements in the wavelength range of 190–1100 nm The optical constants were calculated from the optical transmittance (T) data such as refractive index (n), extinction coefficient (k) and reflectance (R). The optical band gap (E_g) of FNS is 3.27 eV with direct transition. The complex dielectric (?) constant of the grown FNS crystal was determined. The second harmonic generation (SHG) efficiency of the grown FNS crystal has been studied by using Kurtz-Perry powder technique and it shows 12 times relatively greater than KDP.     

Crystal structure and thermal behavior of two new organic monosulfates NH3(CH2)5NH3SO4 1.5H2O and NH3(CH2)9NH3SO4 H2O

The chemical preparation, the calorimetric studies and the crystal structure are given for two new organic sulfates NH₃(CH₂)₅NH₃SO₄ 1.5H₂O (DAP-S) and NH₃(CH₂)₉NH₃SO₄·H₂O (DAN-S). DAP-S is monoclinic P2₁/n with unit cell dimensions: a=11.9330(2) Å; b=10.9290(2) Å; c=17.5260(2) Å; β=101.873(1)°; V=2236.77(6) Å³; and Z=8. Its atomic arrangement is described as inorganic layers of units and water molecules separated by organic chains. DAN-S is monoclinic P2₁/c with unit cell parameters: a=5.768(2) Å; b=25.890(10) Å; c=11.177(5) Å; β=115.70(4)°; V=1504.0(11) Å³ and Z=4. Its structure exhibits infinite chains, parallel to the [100] direction where the organic cations are interconnected. In both structures a network of strong and weak hydrogen bonds connects the different components in the building of the crystal.     

Harmonic Mode-Locked Er-Doped Fiber Laser by Evanescent Field-Based MXene Ti3C2Tx (T = F,O, or OH) Saturable Absorber

MXenes, as a legendary family of 2D van der Waals nanosheets materials, are extensively studied due to their unique characteristics of broadband nonlinear optical response. In particular, MXenes have excellent nonlinear optical properties of very large nonlinear absorption coefficients and very large nonlinear refractive indexes, which have attracted people's great attentions to study the application of MXenes in photonics, electronics, and optoelectronics in recent years. However, the high-repetition-rate (HRR) ultrafast pulses are not explored based on these kinds of materials. MXene Ti₃C₂T_x saturable absorber (SA) based on micro-fiber is fabricated by optical deposition method. Here, MXene Ti₃C₂T_x SA is used to achieve 36th harmonic mode-locking with a repetition rate of 218.4 MHz, a central wavelength of 1566.9 nm, the pulse width of 850 fs, and the spectral width of 3.51 nm. The maximum average output power and pulse energy are 6.95 mW and 0.032 nJ, respectively. This research based on MXene Ti₃C₂T_x light modulator opens a bright avenue for advanced nonlinear photonics.     

聚片多畴LiNbO3晶体的倍频效应

通过对聚片多畴LiNbO₃晶体倍频效应的研究,从实验上对Bloembergen等人所提出的准位相匹配理论进行了细致的检验。首先运用Maker条纹法在实验上直接测定了单畴LiNbO₃晶体在e^ω·e^ω→e^2ω非位相匹配下的倍频光强,并采用角度扫描和温度扫描方法,以获得满足准位相匹配条件时的不同片数的聚片多畴晶体的最大倍频强度,从而验证了聚片多畴晶体倍频相对光强与片畴数N成平方关系。在N<200时,取得 关键词：     

Studies on physico-chemical properties of hydroxyethylammonium (l) tartrate monohydrate single crystals

In this paper, we report the growth and characterization of hydroxyethylammonium (l) tartrate monohydrate single crystals grown by slow evaporation solution technique. The X-ray diffraction analysis reveals that the crystal belongs to the monoclinic system having P2₁ space group. Photoinduced optical absorption effects were studied on the crystalline samples irradiated with CW 532 nm (green) and 689 nm (red) laser wavelengths. The relative second harmonic generation efficiency of the title crystal was found to be 1.4 times larger than that of KDP crystal. The thermal, mechanical, dielectric and optical studies of the single crystals were carried out to propose the material for useful applications. The reflectance and refractive indices were also evaluated from optical transmission spectrum. Further the electronic excitation calculations were carried out to understand the charge transfer mechanisms.     

All solid-state continuous-wave Nd:YAG laser at 1319 and 659.5 nm under direct 885 nm pumping

The continuous-wave high efficiency laser emission of Nd:YAG at the fundamental wavelength of 1319 nm and its 659.5-nm second harmonic obtained by intracavity frequency doubling with an LBO nonlinear crystal is investigated under pumping by diode laser at 885 nm (on the ⁴ F _3/2 → ⁴ I _13/2 transition). An end-pumped Nd:YAG crystal yielded 9.1 W at 1319 nm of continuous-wave output power for 18.2 W of absorbed pump power. The slope efficiency with respect to the absorbed pump power is 0.55. Furthermore, 5.2 W 659.5 nm red light is acquired by frequency doubling, resulting in an optical-to-optical efficiency with respect to the absorbed pump power of 0.286. Comparative results obtained for the pump with diode laser at 808 nm (on the ⁴ F _5/2 → ⁴ I _13/2 transition) are given in order to prove the advantages of the 885 nm wavelength pumping.     

Photoinduced second harmonic generation studies on Tris(thiourea)copper(I) perchlorate Cu(SC(NH2)2)3(ClO4)

We have established a possibility to obtain the photoinduced optical second harmonic generation in the initially centrosymmetric single crystals of tris(thiourea)copper(I) perchlorate crystallized in the monoclinic system with the space group P2₁/c. The second‐order susceptibility of the investigated crystal was measured by inducing the crystal by external laser field. The results obtained are interesting and discussed in detail. We have established that the optical second harmonic generation achieves its maximum (about 0.84 pm/V) at photoinducing power density about 1430 kW/cm² for the fundamental wavelength 1064 nm. The maximal output second harmonic generation (SHG) was achieved at an angle of about 35° between the pumping and fundamental power beam's polarizations. Such maximum may be a consequence of a competition between the so formed anharmonic photothermal expansions and the thermal destruction that occurred because of the heating of the crystal surfaces. Our independent verifications have shown that the photoinduced surfaces were heated up to 8–12° C. This may cause occurrence of photothermal relaxation processes. The output SHG exists only immediately after the act of photoinduction. The obtained dependences are caused by specific features of the Raman spectra of the investigated crystals. Copyright © 2008 John Wiley & Sons, Ltd.     

Kilohertz high power extracavity KGW yellow raman lasers based on pulse LD side-pumped ceramic Nd: YAG

We report an efficient operation of a kilohertz nanosecond extracavity KGd(WO₄)₂ (KGW) crystal Raman yellow laser, which is pumped by a 532 nm lasers based on pulse laser diode (LD) side-pumped ceramic Nd: YAG, BBO electro-optical Q-switched and LBO crystal extracavity frequency doubling. With the 5 W, 10 ns and 1 kHz output power pumped at 532 nm, we obtained 2.58 W, 7.4 ns, 1 kHz second Stokes Raman laser output at 579.54 nm for 768 cm⁻¹ Raman shift of KGW crystal, corresponding to a conversion efficiency of 51.4%. By changing the KGW crystal orientation, we further obtained 3.18 W, 7.8 ns, 1 kHz Raman pulses at 588.33 nm for 901 cm⁻¹ Raman shift, corresponding to a conversion efficiency of 63.3%. The beam quality factors M² of 579.54 and 588.33 nm were (M _x−579.54² = 5.829, M _y−579.54² = 6.336) and (M _x−588.33² = 6.405, M _y−588.33² = 6.895), respectively.     

Structure and NLO property relationship in a novel chalcone co-crystal

Single crystals of a chalcone co-crystal (C₁₈H₁₉NO₄/C₁₇H₁₆NO₃Br; 0.972/0.028) have been grown by slow evaporation from solution. The powder second harmonic generation (SHG) efficiency of this chalcone co-crystal is 7 times that of urea. The dependence of second harmonic (SH) intensity on particle size revealed the existence of phase matching direction in this crystal. The large SHG efficiency observed is mainly due to the unidirectional alignment of molecular dipoles, in which the dipole moment of each molecule adds to establish a net polarization. The weak N–H⋅⋅⋅O hydrogen-bond interactions help to stabilize the noncentrosymmetric crystal packing and also contribute partly to the SHG. The better thermal stability, transparency and high laser damage resistance (>1.5 GW cm⁻² at 532 nm, 8 ns) of this chalcone co-crystal indicate that it is a promising material for frequency doubling of diode lasers down to 470 nm. This molecule also shows a third-order NLO response and good optical limiting property of 8 ns laser pulses at 532 nm. The mechanism for optical limiting in this chalcone was attributed to two-photon induced excited state absorption that leads to reverse saturable absorption. The structure–property relationship in this chalcone and related compounds is discussed based on the experimental results and semiempherical hyperpolarizability calculations.     

Growth and physical properties of an organic crystal for NLO applications: Guanidinium phenyl arsonate (GPA)

Single crystals of organic material guanidinium phenyl arsonate (GPA) of size 28 × 14 × 10 mm³ were grown from propanol–water mixed solvent by slow solvent evaporation technique. The crystal belongs to monoclinic system with noncentrosymmetric space group Cc. The lattice parameter values of GPA crystals are a = 18.453 Å, b = 7.609 Å, c = 12.592 Å and β = 121.856°. The grown crystal was subjected to X-ray diffraction (XRD) study to identify its morphology and structure. Chemical etching study using propanol–water as etchant reveals the mechanism of growth. The formation of synthesized compound was confirmed by Fourier transform infrared (FT-IR) spectroscopy analysis. Optical transmittance and second harmonic generation (SHG) of the grown crystals were studied by UV–vis–NIR spectrum and Kurtz powder technique respectively. The transmittance of GPA has been used to calculate the refractive index ‘n’ and the extinction coefficient ‘k’. The laser induced surface damage threshold for the grown crystal was determined using Nd:YAG laser. The mechanical behavior of GPA was analyzed using Vickers microhardness test.     

Laser-induced changes in the electron density distribution of crystals: Ca3Cr2Si3O12

Difference of electron density distribution between a crystal being He–Ne laser-irradiated and non-irradiated has been investigated by in situ X-ray diffraction methods. Difference Fourier analysis between these data revealed electron density decrease of 2.1 eÅ^–3 at the trivalent site occupied 64% by Cr³⁺, the absorbant; while the calcium, silicon, and oxygen sites remained practically unchanged. Crystal data: [Natural uvarovite from Outokumpu, Finland; Ca₃(Cr_1.284Al_0.692Fe_0.024)Si₃O₁₂ (EPMA analysis); Cubic garnet structure; ;Z=8;a ₀=11.936(1) Å;V=1700.5 ų D _x =3.775 Mgm^–3; (MoK)=0.71069 Å; =4025 m^–1;F(000)=1900;T=293 K].     

Synthesis, crystal growth and characterization of a chiral compound (triphenylphosphine oxide cadmium iodide): A new semiorganic nonlinear optical material

Synthesis of semiorganic material, triphenylphosphine oxide cadmium iodide (TPPOCdI), is reported for the first time. Employing the temperature reduction method, a crystal of size 16×7×6 mm³ was grown from dimethyl sulfoxide (DMSO) solution. Three dimensional crystal structure of the grown crystal was determined by single crystal X-ray diffraction study. The complex crystallizes in the chiral orthorhombic space group P2₁2₁2₁. FTIR study was carried out in order to confirm the presence of the functional groups. UV-vis-NIR spectral studies show that the crystal is transparent in the wavelength range of 290-1100 nm. The microhardness test was carried out, and the load hardness was measured. Thermogravimetric and differential thermal analyses reveal the thermal stability of the crystal. Second harmonic generation efficiency of the powdered TPPOCdI, tested using Nd: YAG laser, is ∼0.65 times that of potassium dihydrogen orthophosphate.