Application of advanced transient laser polarimetry to study of nonlinear reflective polarisation phenomena in solids

Abstract

A novel femtosecond time-resolved polarimeter for reflective measurements was developed. The instrument was used with a picosecond Nd:YAG laser and an advanced femtosecond Ti:Sapphire laser. Sensitivity to pump-induced reflected probe polarisation rotation of better than 10^-6 radians combined with time resolution up to 70 femtoseconds has been achieved. Time resolution of 30 femtoseconds was achievable with loss of sensitivity of approximately an order of magnitude. The polarimeter has been tested in a variety of spectroscopic configurations and with different types of solids (metals, semiconductors and superconductors) and was found to be a useful tool for the investigation of the transient nonlinear optical properties of opaque materials. A new type of optical autocorrelator for measurement of the duration of femtosecond optical pulses utilizing a reflective polarisation effect in metallic nickel was designed.

The recently developed spectroscopic polarimetric technique of the Specular Inverse Faraday effect was for the first time used to study a semimagnetic semiconductor (Cd_0.6Mn_0.4Te), a high T_c superconductor (YBaCuO_7-δ) and a ferromagnetic metal (Ni). The cubic optical nonlinearity (χ⁽³⁾₁₁₂₂ - χ⁽³⁾₁₂₂₁) was measured in these opaque solids for the first time. In particular, in nickel a strong (χ⁽³⁾ ~ 2 x 10^-9esu) and exceptionally fast (τ < 30 fs) nonlinearity, which is promising for reflective nonlinear optical applications, was found. The thermalisation and spin-relaxation dynamics in GaAs were investigated with femtosecond time resolution using Specular Inverse Faraday effect spectroscopy for the first time.

Investigations were undertaken into natural and light induced reflective anisotropy in zincblende structure crystals. Transient measurements of induced anisotropy, its orientation dependence and intensity dependence were made for the first time in GaAs, InSb and Cd_0.6Mn_0.4Te. Analysis of microscopic and macroscopic pictures of the light-matter interaction in zincblende structure materials allowed attribution of the observed anisotropic effects to the phenomenon of natural and induced gyrotropic linear dichroism.

A computer program based on the quaternion description of light polarisation, the constitutive equation and the wave equation and suitable for calculation of evolution of partially polarised light in linear and nonlinear optical media with local and nonlocal optical response has been developed. The evolution of the polarisation state of partially polarised light during propagation in an isotropic medium with cubic nonlinearity has been investigated in detail and compared with published analytical and semi-analytical data.

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Identifiers

ORCID for Nikolay Zheludev: orcid.org/0000-0002-1013-6636

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