Measurement of nonlinear refractive index coefficient of inert gases with hollow-core fiber
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Measurement of nonlinear refractive index coefficient of inert gases with hollow-core fiber Ding Wang • Yuxin Leng • Zhizhan Xu
Received: 22 July 2012 / Accepted: 24 January 2013 / Published online: 7 February 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract A simple method of determining the nonlinear refractive index coefficient n2 of inert gases is demonstrated. It is based on the accumulation of optical-Kerr-induced spectral broadening effect in gas-filled hollow-core fibers. By using this method, the values of n2 of argon and neon at 800 nm and argon at 1.8 lm are determined.
1 Introduction Non-resonant optical-intensity-dependent refractive index is very important in ultrafast laser science and technology. For example, this intensity-dependent refractive index plays a key role in ultrafast pulse propagation dynamics in transparent media, such as pulse compression down to few optical cycles [1], filamentation [2], optical soliton interactions [3], and so on. This effect originates from the third order of nonlinearity and is described as a modification of n2I to the linear refractive index [4], where I is the optical intensity and n2 is nonlinear refractive index coefficient. This modification in refractive index could lead to effects like temporal chirping and spectrum broadening of optical pulse, as well as self-focusing in spatial domain. Many applications of modern lasers benefit from these effects such as Kerr-lens mode-locked Ti:sapphire oscillators [5] and atmospheric LiDAR [6]. On the other hand, there are also many situations suppressing them, like transportation
D. Wang (&) Y. Leng Z. Xu State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China e-mail: [email protected] Y. Leng e-mail: [email protected]
of high-field laser pulses [7] to targets for light–matter interaction research under extreme conditions. For both ends, an easy way to measure the parameter n2 under different working wavelengths and conditions will be beneficial. Experimentally determination of n2 for various materials has been a research interest since the 1970s. Up to now, there are many ways to measure n2 for different materials under different conditions. Depending on the number of beams involved in the measurement, these methods can be divided into single-beam method and multi-beam method. Multi-beam method, such as degenerate four-wave mixing [8], polarization spectroscopy [9], spectral interferometry [10], spectrally, spatially resolved interferometer [11], and so on, usually needs complex experimental apparatus and requires a strict spatial overlap of different beams, compared with single-beam method. Although the multi-beam method can give very accurate results, the single-beam method can also provide adequate accuracy in most cases, such as the powerful and widely used Z-scan method [12]. However, Z-scan method requires a tight focusing geometry, which limits the light–matter interaction region to \1 cm. This is th
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