High-accuracy measurements of the refractive index and its temperature coefficient of calcium fluoride in a wide wavelength range from 138 to 2326 nm

The refractive indices of synthetic calcium fluoride for 69 wavelengths from 138 nm in the deep ultraviolet to 2326 nm in the near infrared were measured by the minimum-deviation method in a nitrogen environment. We made these measurements at 20 degrees and 25 degrees C, respectively, to determine the thermal coefficients of the refractive index over this wide-wavelength region. These refractive indices were fitted to a four-term Sellmeier dispersion formula. The temperature coefficients of the refractive index were fitted to a Hoffman-type dispersion formula. The standard deviation of the residual between the observed values and the calculated values was 0.6 x 10(-6) for the refractive index and was 0.13 x 10(-6)/degrees C for the temperature coefficient of the refractive index.     

无汞平面光源亮度与发光效率的优化

为了提高无汞平面光源的发光效率和避免放电收缩,本文设计并制作了一种新型的具有弧形电极结构的12寸无汞平面光源,基于该新型结构光源,对不同气压下Ne+Xe(10%),Ne+Xe(15%),Ne+Xe(30%)三种混合气体的光电特性以及驱动脉冲波形的上升沿对亮度及系统发光效率的影响进行了研究与分析。实验结果表明,平面光源的亮度随着气压的升高以及Xe含量的增加而升高,在60 kPa时采用Ne+Xe(30%)气体,其平均亮度可达7500 cd/m2;在气压低于60 kPa时,发光效率随气压的升高而急剧上升,随着气压的进一步升高以及Xe含量的增加,发光效率上升趋势逐渐变缓,甚至呈下降的趋势,在50 kPa时采用Ne+Xe(30%)系统最高发光效率可达23.7 lm/W;另外,通过优化驱动波形的上升沿,可以进一步提高平面光源的亮度及光效(约10%)。     

Measurement of the refractive index of distilled water from the near-infrared region to the ultraviolet region

By the minimum deviation method using a prism shaped cell, the absolute refractive indices of high-performance liquid chromatography distilled water were measured at the wavelengths from 1129 to 182 nm, at the temperature of 19 degrees C, 21.5 degrees C, and 24 degrees C, and then dn/dt at 21.5 degrees C was calculated. The coefficients of the four-term Sellmeier dispersion formula were determined by using the refractive indices at each temperature. As a result of the comparison of our refractive index data in the visible wavelength region with the formula by Tilton et al. at the National Bureau of Standards in 1938, both the refractive index data corresponded within 6 x 10(-6). In the UV region, the absolute refractive index at 193.39 nm calculated by the data measured nearby the wavelengths from 200 to 190 nm was 1.436517 (21.5 degrees C). The value was lower by 9 x 10(-5) or 10 x 10(-5) than the data measured by Burnett et al. at the National Institute of Standards and Technology.     

玻璃材料折射率及色散的高准确度测量

使用德国Triotics公司生产的SpectroMaster HR UV-VIS-IR型折射率测量设备,对FK5玻璃块的e、d、g、F′和C′谱线的折射率值进行高准确度测量,并修正至标准环境条件下的折射率值。用得到的折射率值进行曲线拟合,验证Cauchy色散公式和Sellmeier色散公式。     

Absolute refractive indices and thermal coefficients of CaF2, SrF2, BaF2, and LiF near 157 nm

We present high-accuracy measurements for wavelengths near 157 nm of the absolute index of refraction, the index dispersion, and the temperature dependence of the index for the ultraviolet optical materials with cubic symmetry: CaF2, SrF2, BaF2, and LiF. Accurate values of these quantities for these materials are needed for designs of the lens systems for F2 excimer-laser-based exposure tools for 157-nm photolithography. These tools are expected to use CaF2 as the primary optical material and possibly one of the others to correct for chromatic aberrations. These optical properties were measured by the minimum deviation method. Absolute refractive indices were obtained with an absolute accuracy of 5 x 10(-6) to 6 x 10(-6).     

Refractive index measurement of cerium-doped LuxY2−xSiO5 single crystal

Principal refractive indices of the biaxial cerium-doped Lu_xY_2−xSiO₅ (LYSO) crystal were determined with high accuracy at seven different wavelengths between 400 and 700 nm using the classical minimum angle of deviation method. The reliability of the measured data permitted to deduce parameters of a common dispersion formula, by which the refractive indices can be extrapolated for wavelengths up to 1100 nm, an important range for laser applications. The extent of axial dispersion was precisely measured by ellipsometry, its effects on the anisotropic refractive index has been calculated. Examples are given to demonstrate the influence of anisotropy on the operation of optical devices.     

Characterization of optical waveguides in YbVO4 crystals formed by 3.0 MeV oxygen ion implantation

We report optical planar waveguide formation in vanadate laser crystals YbVO(4) by oxygen ion implantation at an energy of 3.0 MeV and doses from 5 x 10(13) to 2 x 10(15) ions/cm(2) at room temperature. Positive changes of the ordinary refractive indices occur in the implanted regions, which define a waveguide structure in the near surface. The relationship between refractive index changes and doses is presented. Waveguide modes were measured at wavelengths of 633 and 1539 nm, respectively. The magnified field pattern of the propagation light in the annealed waveguide was captured and studied by an end-coupling method. The refractive index profiles were reconstructed by the reflectivity calculation method.     

Linear and nonlinear optical properties of ZnGeP2 crystal for infrared laser device applications: revisited

Measurement of refractive indices in the spectral bands 9-11 microm and 1.32 microm from a cw CO2 laser and a Q-switched Nd:YAG laser, respectively, is reported in a ZnGeP2 crystal. A new set of Sellmeier dispersion relations has been derived from the measured refractive indices data in this crystal. Second-harmonic generation (SHG) of CO2 laser radiation in this crystal is also reported. It is also seen that the previously reported phase-matching data for others experiments in SHG and optical parametric devices is explained satisfactorily with this new set of Sellmeier dispersion relation.     

Use of radiation and hybrid modes to increase the accuracy in the determination of the refractive indices of rutile

A new method to correlate prism and substrate refractive indices is presented and applied to the determination of rutile refractive indices, both ordinary and extraordinary, at different wavelengths in the visible and the near infrared. The method exploits radiation modes and, when the sample structure allows it, hybrid modes. An accuracy of approximately 2 x 10(-4) was achieved without the need of any specific preparation of the samples. The method exhibits a good versatility since it can be exploited for the determination of the refractive index of a coupling prism when the substrate index is known and vice versa.     

Measurement of Refractive Nonlinearities in GaAs Above Bandgap Energy

We present a technique for single-beam measurement of the optical nonlinearity in GaAs for photon energies above the bandgap. We measured the real and the imaginary parts of the nonlinear refractive index of a bulk crystal by using the change in reflection of dye laser pulses (10 ns, 538 nm). The values obtained, n(2) = (7.8 ? 0.6) x 10(-8) cm(2)/W and kappa(2) = (-2.8 ? 0.7) x 10(-8) cm(2)/W, are discussed.     

Direct measurement of the group refractive index of air with interferometry between adjacent femtosecond pulses

The group refractive index of air in laboratory conditions is measured directly between adjacent femtosecond laser pulses by a new interferometry technique. Measurement of the repetition rate of the mode-locked pulse train that gives the maximum amplitude of the interference-signal envelope enables us to determine the group refractive index of air within a standard deviation of 2 x 10(-7). This simple method without vacuum reference is attractive for measuring the group refractive index needed for precise distance measurements in open fields.     

Trace-gas detection in ambient air with a thermoelectrically cooled, pulsed quantum-cascade distributed feedback laser

A pulsed quantum-cascade distributed feedback laser operating at near room temperature was used for sensitive high-resolution IR absorption spectroscopy of ambient air at a wavelength of ~8 mum. Near-transform-limited laser pulses were obtained owing to short (~5-ns) current pulse excitation and optimized electrical coupling. Fast and slow computer-controlled frequency scanning techniques were implemented and characterized. Fast computer-controlled laser wavelength switching was used to acquire second-derivative absorption spectra. The minimum detectable absorption was found to be 3 x 10(-4) with 10(5) laser pulses (20-kHz repetition rate), and 1.7 x 10(-4) for 5 x 10(5) pulses, based on the standard deviation of the linear regression analysis.     

Optical breakdown in fused silica and argon gas: application to Nd:YAG laser limiter

A gas cell filed with argon gas under pressure is placed in a tightly focused laser beam to provide a limiter for laser pulses above a certain peak power, corresponding to the optical breakdown threshold for the creation of a laser-induced plasma. Measurements of the threshold intensity as a function of argon gas pressure are given for a laser wavelength of 1.064 microm (Nd:YAG) and a pulse length of 6.4 ns. Threshold intensities for optical breakdown in fused silica were measured with the same optical system, enabling a relative comparison of breakdown thresholds, of interest for protecting fused-silica optical components in fiber-optic delivery systems for laser material processing applications. The threshold intensity was measured to 220 GW/cm2 in Ar at 1.0 x 10(5) N/m2 (1 atm), 80 GW/cm2 in Ar at 8.0 x 10(5) N/m2 (7.9 atm), and 55 GW/cm2 in fused silica. Even though the threshold in argon is higher than that in fused silica, the limiter will protect the optical components if the laser beam is focused to a tighter spot in the gas cell than at the input end of the fiber.     

Effect of Temperature on the Refractive Index of Aliphatic Hydroxilic Mixtures (C2–C3)

The refractive indices of mixtures of ethanol+(1-propanol, 2-propanol, 1,2-propanediol, and 1,3-propanediol) have been measured at temperatures of 288.15, 293.15, 298.15, and 303.15 K at atmospheric pressure. In this work, an analysis of the mixing properties gives valuable information on packing trends, showing the interactions of ethanol in a hydroxilic environment. From the measured refractive indices on mixing, the parameters of a set of analytical expressions, which represent the composition and temperature dependences of the derived property, are reported. The excess molar volumes are estimated using derivations of the Heller equation, which are dependent on the refractive indices on mixing; accurate values are obtained for the alcohol mixtures, using literature data. The effect of temperature on the mixing and derived properties is analyzed in terms of the relative position of hydroxyl groups, the alkyl chain length, and the available hydrogen-bond interactions between solute and solvent molecules.     

Approximation of flammability region for natural gas-air-diluent mixture

The growing implementation of exhaust gas recirculation (EGR) in reducing NO(x) emissions of engine is of paramount motivation to perform a fundamental research on the flammability characteristics of fuel-air-diluent mixtures. In this work, the influences of EGR on the flammability region of natural gas-air-diluent flames were experimentally studied in a constant volume bomb. An assumption of critical burning velocity at flammability limit is proposed to approximately determine the flammability region of these mixtures. Based on this assumption, an estimation of the flammability map for natural gas-air-diluent mixtures was obtained by using the empirical formula of burning velocity data. The flammability regions of natural gas-air mixtures with EGR are plotted versus the EGR rate. From the comparison of estimated results and experimental measurements, it is suggested that the accuracy of prediction is largely dependent upon the formula of burning velocity used. Meanwhile, the influence of pressure on the critical burning velocity at flammability limit is also investigated. On the basis of the pressure dependence criterion, the estimation was performed for the circumstance of high temperature and pressure, and the prediction results still agree well with those of experiments.     

Gain measurements in the KrCl excimer laser

The single-pass/double-pass amplified spontaneous emission technique has been used to measure the net gain at 222.4 nm in a discharge-pumped UV-preionized KrCl laser. The net gain has been measured as a function of pump rate and total pressure in He- and Ne-based gas mixtures. A maximum net gain of 0.15 cm(-1) has been obtained in a 0.09% HC1/10.1% Kr/1.5% He/88.3% Ne mixture at a total pressure of 355 kPa and at a specific power loading of approximately 21 MW/cc. The data presented are compared with previous net gain measurements performed using the passive absorption cell method.     

Determination of size, refractive index, and dispersion of single droplets from wavelength-dependent scattering spectra

Intensities of light scattered in the planes parallel and perpendicular to the polarization plane of the incident light are used to determine the size, refractive index, and dispersion of a single droplet suspended in an electrodynamic balance. Wavelengths of TE- and TM-mode resonances are determined independently with high precision when a ring dye laser is scanned. Resonating wavelengths are matched with theoretical intensity peaks to determine the constants of a dispersion formula and the size that minimizes the difference between observed and calculated wavelengths. The procedure permits the determination of the size and refractive index with relative errors of 3 × 10(-5) and dispersion with an absolute error 2 × 10(-5) over the experimental spectral range.     

Influence of surrounding media refractive index on the thermal and strain sensitivities of long-period gratings

A detailed study of the thermal and strain sensitivities of a long-period grating when the device is immersed in different external media is presented. The range of refractive indices analyzed are within 1.000 to 1.447, corresponding to samples of air, water, ethanol, naphtha, thinner, turpentine, and kerosene. Within the same range of refractive indices, the strain sensitivity is between (-0.24 +/- 0.03) and (-0.94 +/- 0.11) pm/microepsilon. For the grating immersed in these fluids, the refractive index sensitivity ranges from -3 to -1035.6 nm per refractive index units. The coupling thermo-optic coefficients and the strain-optic coefficients are also measured, resulting in the range from (2.45 +/- 0.04)x10(-5) to (15.89 +/- 0.82)x10(-5) deg C(-1) and (-1.15 +/- 0.04) to (-1.61 +/- 0.04) microepsilon(-1), respectively. A noticeable nonlinear behavior of the thermal sensitivity is found for external media with refractive indices higher than 1.430.     

基于Edlén公式空气折射率测量系统的校准研究

为了检验对激光干涉仪测量精度有很大影响的空气折射率测量系统的测试性能,提出一种可用于基于Edlén公式的空气折射率测量系统的校准方法,并且设计了专门的校准装置,该装置主要由温度、气压以及湿度测量系统组成。实验证明：取包含因子k=2时,温度在(5~40)℃区间,测量不确定度U优于0.02 ℃;气压在(66~105)kPa区间,U=18 Pa;湿度在(10~90)%RH区间,U=2.0%RH,等效于整个系统对应的空气折射率测量的相对不确定度优于1×10^-7     

Decoupling refractive index and geometric thickness from interferometric measurements of a quartz sample using a fourth-order polynomial

A Michelson interferometer setup was used to determine refractive index and thickness of a fused-quartz sample with no knowledge of either parameter. At small angles, < 10 degrees, the interferometer equation follows a fourth-order polynomial in the sample refractive index alone, effectively decoupling the sample thickness from the equation. The incident angle of the He-Ne laser beam versus fringe shift was fitted to the polynomial, and its coefficients obtained. These were used to determine refractive index to within 6 x 10(-4) of the known value with an accuracy of +/- 1.3%. Sample thickness was determined to an accuracy of +/-2.5%. Reproducibility of the rotating table was determined to be +/-2 x 10(-3) degrees.