Workshop on High-Field THz Science High Power THz Generation and THz Field Enhancement in Nanostructures

Fabian Brunner1, Salvatore Bagiante2, Florian Enderli1, Justyna Fabianska1, and Thomas Feurer1

1Institute of Applied Physics, University of Bern, Switzerland2Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, Switzerland

Outline

> Introduction: Applications of strong electric and magnetic fields at THz frequencies

> Generation of intense THz pulses in nonlinear optical crystals

> THz field enhancement in metallic nanostructures> THz SHG in lithium niobate crystals> Conclusions

Outline 2

Applications of strong electric and magnetic fields at THz frequencies

> Nonlinear optics at THz frequencies (bulk semiconductors, quantum dots, …)

> Direct excitation of transverse optical phonons or anti-ferromagnetic spin waves

> Acceleration of charged particles and measurements of electron bunch profiles (THz streak camera)

> Single shot imaging> …

Introduction 3

Efficient THz generation in NLO crystals:Requirements for the crystals

> A large tensor element of the nonlinear optical susceptibility

> Low linear and nonlinear optical absorption> Low THz absorption> Phase-matching:

— collinear:(organic nonlinear optical crystals: DAST, OH1,…)

— Cherenkov-type:(LiNbO3)

THz generation in nonlinear optical crystals 4

High power THz time-domain spectroscopy

5

Comparison of laser-based methods for THz pulse generation

6

Peak electric field vs. pulse energy

Assumptions:> Single cycle pulse> Focusing with F# = 1

7

Non-resonant enhancement:array of slits

8

Gold slit array on silicon

Typical field enhancement of a slit

Ideal periodicity of slit array

> most effective harvesting of incident field

9

> Nonlinear signal: trade-off between volume of high field strength and high field enhancement

Resonant enhancement:Split ring resonators

10

31 nm

Second harmonic generation in LiNbO3

Simulated spectra of transmitted pulses

11

Fabrication of the sample

Conclusions

> Combination of high power THz source with local field enhancement enables new experiments

> Fabrication of gold nano-structures on silicon> New fabrication process for gold nano-slits filled with

lithium niobate> Simulation of SHG spectra and optimization of geometry

parameters for the highest conversion efficiency

12