Elsevier

Chemical Physics Letters

Volume 369, Issues 3–4, 17 February 2003, Pages 318-324
Chemical Physics Letters

An experimental investigation of the nonlinear refractive index (n2) of carbon disulfide and toluene by spectral shearing interferometry and z-scan techniques

https://doi.org/10.1016/S0009-2614(02)02021-3Get rights and content

Abstract

The recently proposed spectral shear interferometry and the well-known z-scan techniques were employed for the determination of the nonlinear refractive index n2 of CS2, toluene and fused silica. The determined n2 values by both techniques were found to be in very good agreement. In addition, the role of the repetition rate of the laser is also investigated revealing its importance for the correct determination of both the size and the sign of the nonlinearity.

Introduction

During the last years the interest for the characterization of the nonlinear optical response of materials has been significantly increased. The emerging need for materials exhibiting properties suitable for ultrafast applications such as optical switching, optical telecommunications, 3D storage, optical limiting etc., has stimulated a lot of research work in this field. In addition to the technological interest for such applications, the fundamental knowledge that can be derived is quite considerable.

Although several experimental techniques have been employed for the determination of the nonlinear optical properties of materials, it is usually difficult and very often not very accurate to measure directly the nonlinear optical parameters. In that respect, the nonlinear response of a given compound can be determined using a reference material. The most frequently used reference material is carbon disulfide (CS2), because it exhibits a large nonlinearity and it is easily available. However, due to the variety of the experimental techniques employed (i.e., DFWM, z-scan, THG, Kerr effect, etc.) and the plethora of the experimental conditions used (i.e., wavelength, repetition rate, pulse duration, etc.), the comparison even with such a reference material becomes sometimes a difficult task since nonlinearities of different physical origin can be determined. As an example, long enough pulses under resonant conditions induce transient response based on excited states population whereas very short pulses measure the pure electronic response.

In the present work we report on the measurement of the nonlinear refractive index n2 of CS2, toluene and fused silica employing two different experimental techniques: the well-known z-scan and the recently proposed spectral shearing interferometry (initially used for the characterization of femtosecond laser pulses). The motivation of this work was both the report of an accurate value of the nonlinear refractive index for materials used as references and an investigation of the possibilities of using the spectral shearing interferometry as a method for the determination of the optical nonlinearities.

Section snippets

Experimental

The first method used relies on spectral shear interferometry. It is often called ‘spectral phase interferometry for direct electric field reconstruction’ (SPIDER) [1] and it was first proposed for the characterization of femtosecond laser pulses [2], [3]. Recently, it was demonstrated that such characterization could also become spatially resolved [4] and that such a scheme can be employed to measure self-phase modulated pulses and the nonlinear refractive index n2 in hydrogen gas and in

Results and discussion

In all experiments performed in the present work and based on the spectral shearing interferometry, a 110 fs chirped pulse amplified Ti:sapphire laser, operating at 800 nm at a repetition rate of 20 Hz was used. The laser energy was measured by means of a Molectron energy meter (J3-09). All materials studied were of spectroscopic quality and were used without further purification in 5 and 10 mm quartz cells. The laser intensity was kept within intensities ranging from 1.9 to 4.2 GW/cm2, the

Conclusions

In the present work we have determined the nonlinear refractive index of CS2 and toluene, two solvents widely used as reference standards. The investigation was carried out in the femtosecond regime, by employing two different experimental techniques, the z-scan and the spectral shearing interferometry. The values of the nonlinear refractive index measured with the two techniques are in good agreement and consistent with others published in the literature. Moreover, to the best of our

Acknowledgements

S.C. acknowledges a Visiting Professorship grant from the University of Bourgogne, where the low repetition rate (10 Hz) experiments were carried out and the University of Patras for partial support through a ‘Karatheodoris’ grant. E.K., X.M. and S.C. wish to acknowledge support from the Ultraviolet Laser Facility, operating at FORTH-IESL through the TMR programme ERBFMGE CT950021. The help of Mr P. Aloukos in the data analysis is also acknowledged.

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Present address: Universite Pierre et Marie Curie, Laboratoire de Physique Moleculaire et Applications-CNRS UMR 7092.

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