Measurement Of Nonlinear Refractive Index Research Articles

Effect of water salinity on the focal tuning of an injected liquid lens used to modify the z-scan method

A water-injected liquid lens is fabricated to tune its focal length using the change in water salinity. It is found that when the salinity of water is changed from zero to 34.25%, the focal length can be changed by about 12.6 mm from 73.7 mm to 86.3 mm. A focal length resolution of approximately 0.75 × 10−2 mm and high temporal stability over a long period have been achieved for the lens foci. This lens is then used to modify the z-scan technique where the lens and the sample both remain fixed without displacement. The performance of the fabricated lens is evaluated by nonlinear refractive index measurement of a sample containing 10.82-pH-synthesized Silver nanoparticles suspended in water with 15 mM of concentration. For verification of the results, a nonlinear refractive index of (−10.6 ± 1.0) × 10−7 cm2 W−1 is firstly measured for the sample using a classical z-scan benefiting from a conventional focal-fixed lens. Interestingly, we found out that when the fabricated lens is replaced in the modified z-scan, the nonlinear refractive index of about (−8.1 ± 0.2) × 10−7 cm2 W−1 can be measured, indicating a similarity in the order and small difference in the coefficient compared to the classical z-scan. This outcome highlights the potential capability and simplicity of the fabricated lens in the modification of the classical z-scan technique.

Measurement of nonlinear refractive indices of bulk and liquid crystals by nonlinear chirped interferometry.

The nonlinear refractive indices (n2) of a selection of bulk (LiB3O5, KTiOAsO4, MgO:LiNbO3, LiGaS2, ZnSe) and liquid (E7, MLC2132) crystals are measured at 1030 nm in the sub-picosecond regime (200 fs) by nonlinear chirped interferometry. The reported values provide key parameters for the design of near- to mid-infrared parametric sources, as well as all-optical delay lines.

Combination of muller matrix polarimetry and z-scan techniques for nonlinear refractive index measurement

Polarization state of light affects the results of nonlinear refractive index measurement. In this work by integrating Mueller matrix polarimetry with z-scan technique, reciprocal effects of optical nonlinearity and polarization is studied. By using classical Muller matrix polarimetry, polarization states generate before the sample in z-scan system and polarization state analyze after sample and before close aperture detector. By using a CW laser at 655 nm wavelength, thermal nonlinear refractive index of an Azo dye, Janus Green B, was measured. The results are very sensitive to polarization states. The measured Muller matrix in each position of sample result the nonlinear dependence of related Deattenuation, Retardance and Depolarization parameters.

Interferometric measurements of nonlinear refractive index in the infrared spectral range.

This study presents the development and application of interferometric technique for the measurement of nonlinear refractive index of optical materials, while directly accounting for experimentally determined laser pulse shape and beam profile. The method was employed in a systematic study of nonlinear refractive index on a series of common optical materials used in near and mid-IR spectral range, where experimental data on nonlinear material properties is still scarce. The values of nonlinear refractive index were determined at 1.03 µm, 2.2 µm, and 3.2 µm. The measurement results are compared to the values determined by previous studies (where available), and the influence of cascaded second-order nonlinearities is discussed.

Sensitivity enhancement of nonlinear refractive index measurement by Gaussian-Bessel beam assisted z-scan method.

Characterizing the nonlinear optical properties of numerous materials plays a prerequisite role in nonlinear imaging and quantum sensing. Here, we present the evaluation of the nonlinear optical properties of Rb vapor by the Gaussian-Bessel beam assisted z-scan method. Owed to the concentrated energy in the central waist spot and the constant intensity of the beam distribution, the Gaussian-Bessel beam enables enhanced sensitivity for nonlinear refractive index measurement. The nonlinear self-focusing and self-defocusing effects of the Rb vapor are illustrated in the case of blue and red frequency detunings from 5S1/2 - 5P3/2 transition, respectively. The complete images of the evolution of nonlinear optical properties with laser power and frequency detuning are acquired. Furthermore, the nonlinear refractive index n2 with a large scale of 10-6 cm2/W is determined from the measured transmittance peak-to-valley difference of z-scan curves, which is enhanced by a factor of ∼ 1.73 compared to the result of a equivalent Gaussian beam. Our research provides an effective method for measuring nonlinear refractive index, which will considerably enrich the application range of nonlinear material.

Tin selenide: A promising black-phosphorus-analogue nonlinear optical material and its application as all-optical switcher and all-optical logic gate

All-optical technique is an effective method to breakthrough the speed limitation of electric devices. Due to the strong nonlinear optical properties, two-dimensional materials have been concerned. As a potential nonlinear two-dimensional material, SnSe has been applied in the field of ultrafast laser generation. The measurement of nonlinear refractive index of SnSe and its nonlinear application is rare. In this paper, SnSe nanosheets are fabricated by a facial Li intercalation-assisted liquid exfoliation method. The nonlinear optical parameters are measured by the Z-scan technology. The SnSe-coated microfiber acted as a nonlinear device to achieve an all-optical switch and an all-optical AND gate. The wavelength-tuning and long-term stability results confirm that SnSe materials are excellent nonlinear optical medium. It is anticipated that SnSe has potential applications in nonlinear photonics devices toward high-performance all-optical signal processing.

Measurement of the Kerr nonlinear refractive index of the Rb vapor based on an optical frequency comb using the z-scan method.

We report the measurement of the Kerr nonlinear refractive index of the rubidium vapor via the high sensitivity z-scan method by using an optical frequency comb. The novel self-focusing and self-defocusing effects of the vapor are presented with red and blue detunings of the laser frequency. The optical nonlinear characteristics of the rubidium vapor are clearly interpreted under different experimental parameters. Furthermore, the Kerr nonlinear refractive index n2 is obtained from the measured dispersion curve, and it basically occurs on the order of 10-6 cm2/W. The evolutions of the Kerr nonlinear coefficient n2 with the laser power and frequency detuning, respectively, are studied. To the best of our knowledge, the use of pulsed lasers to measure the Kerr nonlinear refractive index n2 of atomic vapor has not been reported yet. The direct measurement of the Kerr nonlinear coefficient will greatly help us understand and optimize nonlinear optical processes and find its more potential applications in quantum optics.

Anisotropic nonlinear refractive index measurement of a photorefractive crystal via spatial self-phase modulation.

We show that the refractive index modification photoinduced in a biased nonlinear photorefractive crystal can be accurately measured and controlled by means of a background incoherent illumination and an external electric field. The proposed easy-to-implement method is based on the far-field measurement of the diffraction patterns of a laser beam propagating through a self-defocusing medium undergoing spatial self-phase modulation. For various experimental conditions, both saturation intensity and maximum refractive index modification have been measured. We also clearly evidence and characterise the anisotropic nonlinear response of the crystal in the stationary regime.

Method for an accurate measurement of nonlinear refractive index in the case of high-repetition-rate femtosecond laser pulses

In this report, we propose a new method for measuring the nonlinear refractive index in liquid and glass samples using femtosecond (fs)-laser pulses with high pulse repetition rates. This method is based on solving the heat equation to derive an expression for the normalized transmittance of closed-aperture Z-scan measurements as a function of the accumulative thermal lens induced by a high-repetition-rate fs laser pulse. To validate this method, the nonlinear refractive indices of acetone as a liquid and soda-lime as a glass material have been measured using a 100 fs pulse duration, 80 MHz repetition rate, and 800 nm wavelength. The extracted nonlinear refractive index is in a good agreement with the reported one using 1 kHz repetition rate fs laser pulses.

Nonlinear refractive index measurement of a trapped particle with Shack–Hartmann wavefront sensor

A technique for nonlinear refractive index measurement of a single trapped nanoparticle is investigated using Shack–Hartmann sensor. In this technique, trapping laser is used as a probe beam and an interacting green laser is illuminated as a pumping beam. Optical path difference and effective height of particle is measured with dual wavelength unwrapping technique. Using the absorption relation, we obtain the profile of nonlinear refractive index. Also, the results prove the quadric relation of the nonlinear refractive index to the nonlinear absorption. This result may have an enormous effect in investigating and characterization of nonlinear refractive index of Nano and Micro-sized particles. Also, measuring the thermal profile of the trapping site after illuminating the high power trapping laser leads to measuring the gradient intensity that could have an important role in nonconservative forces measurements. Another advantage is in having the effective thickness of particle which is important while geometry of the particle is crucial for determining trap stiffness. This measurement may lead to adaptive trap shape control and potential well measurement.

Nonlinear refractive index measurement by SPM-induced phase regression.

Herewith, we describe how intensity and phase of the ultrashort pulse retrieved with second-harmonic frequency-resolved optical gating (SHG FROG) can be utilized for measurement of the nonlinear refractive index (n2). Through comparison with available literature, we show that our method surpasses Z-scan in terms of precision by a factor of two, and thus, constitutes an interesting alternative. We present results for various materials: fused silica, calcite, YVO4, BiBO, CaF2, and YAG at 1030 nm. Unlike the Z-scan, the use of this method is not restricted to free-space geometry, but due to its characteristics, it can be used in integrated waveguides or photonic crystal fibers as well.

Femtosecond laser inscription of nonlinear photonic circuits in Gallium Lanthanum Sulphide glass

We report on femtosecond laser writing of single mode optical waveguides in chalcogenide Gallium Lanthanum Sulphide (GLS) glass. A multiscan fabrication process was employed to create waveguides with symmetric single mode guidance and low insertion losses for the first time at 800 nm wavelength, compatible with Ti:Sapphire ultrafast lasers and nonlinear photonics applications. μRaman and x-ray microanalysis were used to elucidate the origin of the laser-induced refractive index change in GLS. We found that the laser irradiation produced a gentle modification of the GLS network, altering the Ga–S and La–S bonds to induce an increase in the refractive index. Nonlinear refractive index measurements of the waveguides were performed by finding the optical switching parameters of a directional coupler, demonstrating that the nonlinear properties were preserved, evidencing that GLS is a promising platform for laser-written integrated nonlinear photonics.

Anomalous behavior of nonlinear refractive indexes of CO2 and Xe in supercritical states.

Direct measurement of pressure dependent nonlinear refractive index of CO2 and Xe in subcritical and supercritical states are reported. In the vicinity of the ridge (or the Widom line), corresponding to the maximum density fluctuations, the nonlinear refractive index reaches a maximum value (up to 4.8*10-20m2/W in CO2 and 3.5*10-20m2/W in Xe). Anomalous behavior of the nonlinear refractive index in the vicinity of a ridge is caused by the cluster formation. That corresponds to the results of our theoretical assumption based on the modified Langevin theory.

Nonlinear refractive index measurements using time-resolved digital holography.

In this Letter, a novel method to evaluate nonlinear refractive index using time-resolved digital holographic microscopy is introduced. To demonstrate the viability of the method, cross-correlative nonlinear refractive index values for sapphire are measured experimentally: 2.75·10-20 m2/W at 1030nm and 4.10·10-20 m2/W 515nm wavelengths. The obtained results for sapphire are compared to those available in literature obtained by other methods.

Measurement of nonlinear refractive indices of air, oxygen, and nitrogen in capillary by changing the temporal width of short laser pulses

Nonlinear refractive indices of air and its constituents were measured as a function of the pulse width in a capillary used to confine the gas and to increase the interaction length. This study was carried out with nonlinear ellipse rotation measurements using an amplified Ti:sapphire laser system providing pulses at 800 nm, continuously tunable from ∼60 fs up to ∼3 ps. Due to the presence of noninstantaneous orientational response, nonlinearities in molecular gases strongly depend on the pulse width. The pulse width dependence and discrimination between instantaneous and noninstantaneous nonlinearities of air gases were obtained with a simple exponential growth model.

Application of Photothermal Digital Interferometry for Nonlinear Refractive Index Measurements within a Kerr Approximation

The methodology of Photothermal Interferometry implemented through off-axis digital holography for the nonlinear refractive index measurements of optical media with the thermal mechanism of nonlinearity is presented. An experimental appraisal is done on the example of chlorophyllin 1% solution in ethyl alcohol. It allows us to estimate the effective value of nonlinear refractive index as −0.65·10−3 cm2/W. The comparison of the experimental result with data obtained by means of a reference approach was performed. Possible errors lead to a mismatch between them are highlighted and analyzed.

Nonscanning Moiré deflectometry for measurement of nonlinear refractive index and absorption coefficient of liquids.

In this work, a nonscanning measurement technique is presented for determining the nonlinear refractive index and absorption coefficient of liquid media based on Moiré deflectometry. In the proposed method two lasers are used: a low power, wide beam as probe and a high power with specific wavelength as a pump. Interaction of the pump laser beam with the nonlinear sample changes the refractive index, which leads to change in convergence/divergence of the collimated incident probe laser beam. The induced deflection is monitored by Moiré deflectometry. If the pump laser has a Gaussian intensity profile, the refractive index profile of the sample is Gaussian, too. Measuring the deflection angle of the probe beam by Moiré fringes deflection, and by using the inverse Abel transform integral, the refractive index profile and nonlinear refractive index can be determined. This method is fast, easy, and insensitive to environmental noise and allows real-time measurement. Also, the refractive index profile of the interacted medium with pump laser can be achieved by this technique. As a liquid sample, a DCJ dye in water solution was studied. The value of nonlinear refractive index, n2, and absorption coefficient, α, were obtained -2.54×10-4 cm2 w-1 and 1.368 cm-1, respectively.

Measurement of large nonlinear refractive index of natural pigment extracted from Hibiscus rosa-sinensis leaves with a low power CW laser and by spatial self-phase modulation technique

We have reported here, for the first time, to the best of our knowledge, a high nonlinear refractive index (n2e) of a natural pigment extracted from Hibiscus rosa-sinensis leaves by using spatial self-phase modulation technique (SSPM) with a low power CW He-Ne laser radiation at 632.8nm. It is found by UV–Vis absorption spectroscopic analysis that chlrophyll-a, chlrophyll-b and carotenoid are present in the pigment extract with 56%, 25% and 19%, respectively. The photoluminescence (PL) emission characteristics of the extracted samples have also been measured at room temperature as well as in the temperature range of 283–333K to investigate the effect of temperature on luminescent properties of the sample. By analyzing the SSPM experimental data, the nonlinear refractive index value of pigment extract has been determined to be 3.5×10−5cm2/W. The large nonlinear refractive index has been assigned due to asymmetrical structure, molecular reorientation and thermally induced nonlinearity in the sample. The presented results might open new avenues for the green and economical technique of syntheses of organic dyes with such a large nonlinear optical property.

Measurement of nonlinear refractive index of organic materials by z-scan

The nonlinear effects characterization by using the Z-Scan transmission technique in many materials has generated great in forest according to the technological necessities. The majority part of the nonlinear effects can be described by the classic electromagnetic theory, with the electrical susceptibility in the constitutive equation that relates the electrical polarization with the electrical field. In this work the sign and refractive index magnitude and the nonlinear absorption coefficient of the following organic substance were determined: methylene-blue, rodamine LD, vegetable powder and gentian violet a hundred percent pure dissolved in isopropyl alcohol, a laser Nd: YAG was used as a source excitation. The bunch of laser was focused with a lens of ten centimeters of focal length; by using a displacement system the sweeping of twenty centimeters was realized. The following results of the normalized curves of the transmittance in function of the z position were obtained applying the Sheik- Bahae theory: The nonlinear refractive index of the dye shows an increase in function of its concentration and the power of exciting of the laser with negative nonlinear sign in the majority of the sample.

Beam deflection measurement of bound-electronic and rotational nonlinear refraction in molecular gases.

A polarization-resolved beam deflection technique is used to separate the bound-electronic and molecular rotational components of nonlinear refractive transients of molecular gases. Coherent rotational revivals from N(2), O(2), and two isotopologues of carbon disulfide (CS(2)), are identified in gaseous mixtures. Dephasing rates, rotational and centrifugal distortion constants of each species are measured. Polarization at the magic angle allows unambiguous measurement of the bound-electronic nonlinear refractive index of air and second hyperpolarizability of CS(2). Agreement between gas and liquid phase second hyperpolarizability measurements is found using the Lorentz-Lorenz local field correction.