Organic crystal-based THz source for complex refractive index measurements of window materials using single-shot THz spectroscopy

Lufan Du,Amrutha Gopal,Falk Ronneberger,Yun Li,Mostafa Shalaby,Franz Roeder,Burgard Beleites

doi:10.1007/s00339-021-04948-1

Abstract

We employed N-benzyl-2-methyl-4-nitroaniline (BNA) crystals bonded on substrates of different thermal conductivity to generate THz radiation by pumping with 800 nm laser pulses. Crystals bonded on sapphire substrate provided four times more THz yield than glass substrate. A pyrodetector and a single-shot electro-optic (EO) diagnostic were employed for measuring the energy and temporal characterisation of the THz pulse. Systematic studies were carried out for the selection of a suitable EO crystal, which allowed accurate determination of the emitted THz spectrum from both substrates. Subsequently, the THz source and single-shot electro-optic detection scheme were employed to measure the complex refractive index of window materials in the THz range.

Highlights

The terahertz (THz) frequency range is usually defined as the spectral regime between 0.1 and 10 THz
Terahertz radiation generated from BNA crystals mounted on glass substrate pumped with NIR laser pulse was detected and characterised using a single-shot electrooptic detection scheme
EO crystals of different detection bandwidths were employed to corroborate the THz spectra. Based on these studies a suitable EO crystal was chosen for the comparative study using BNA crystals mounted on substrates of different thermal conductivity

Summary

Introduction

The terahertz (THz) frequency range is usually defined as the spectral regime between 0.1 and 10 THz. Theoretical and experimental studies have shown that strong terahertz fields can be used to excite nonlinear responses in materials [14,15,16]. Thanks to their non-ionising nature, THz radiation can be employed for biochemical analysis [17, 18]. The availability of high power THz sources based on organic crystals accelerated this growth thanks to their simpler experimental schemes and phase matching at commonly available laser wavelengths. Different methods and techniques existing in laser technology, such as external cooling or bonding with substrate materials having high thermal conductivity, could be implemented to increase the THz yield [27, 28].

Methods

Results

Conclusion