THz Pulsed Imaging and Spectroscopy

Model: TPS Spectra 3000 (TeraView – UK)
Contact person: Laura Mihai
Tel: +4021 457 4550/ ext. 2501
 
Location: CETAL – Photonics Investigations Laboratory (Room A206)
Financing project: CETAL

http://www.teraview.com/products/terahertz-pulsed-spectra-3000/index.html

System Components

  • Laser Source: Er: doped fibre laser, 780 nm pulses; sub-100 fs, repetition rate of 100 MHz, average output power of >65 mW.
  • GaAs photo-conductive emitter / receiver
  • closed cycle water cooler
  • Sample Transmission module
  • ATR (Attenuation Total Reflection) module
  • RIM (Reflectance Imaging) module
  • XY Mapping module (Transmission stage)

Performances

  • Spectral range:

0.06THz – 3THz(2cm-1 – 100cm-1)

  • Dynamic range > 4 OD @ 0.9THz (30cm-1) in transmission
  • Spectral resolution 0.0075THz (0.25cm-1)
  • 30 scans/second with 1.2cm-1 spectral resolution (for transmission and ATR modules)

Features

  • 35° ATR- larger penetration depths for general purpose measurements
  • Small amounts of sample are placed on the ATR crystal and measured directly with no sample preparation. Solids, powders and gels can all be measured in this way.
 

In XY mapper transmission spectra to be collected at different points on the sample

  • max. scanned area: 19mm x 19mm
  • spacing between points of 50 and 500 microns

In RIM module:

  • max. scanned area is 100mm x 100mm
  • with a user-selected distance between measurement points
  • up to 3mm penetration depth
  • Nitrogen purged sample compartment as standard
  • Ambient temperature operation of both the solid state emitter and detector
  • RIM module:  XY and thickness mapping can be generated from the data collected à physical features: buried cracks, defects and air pockets can be non-destructively detected.

XY Mapper Module (with Transmission Stage)

Sample Transmission Module

Reflectance Imaging Module

Attenuation Total Reflection Module

Technology

The generation of terahertz pulsed radiation is based on a photoconductive switch. Terahertz photoconductive emitters rely on the production of few-cycle terahertz pulses using an ultrafast (femtosecond) laser to excite a biased gallium arsenide antenna. This technique is inherently broadband, with the emitted power distributed over a frequency range of several terahertz (typically 0.06 THz – 3 THz, corresponding to 2 cm-1 – 100 cm-1). Pulsed terahertz emission in photoconductive antennae is produced when the current density, j, of a biased semiconductor is modulated on sub picosecond timescales ETHz ∞ dj/dt. The change in current density, and hence photo current, arises from two processes: 1) the rapid change of the carrier density via femtosecond laser illumination and 2) the acceleration of photo-generated carriers under an external electric field.

Coherent detection of the terahertz radiation is performed in a similar photoconductive antenna circuit. By gating the photoconductive gap with a femtosecond pulse synchronized to the terahertz emission, a current proportional to the terahertz electric field is measured. By varying the optical path length to the receiver, the terahertz time domain can be sampled. Hence both the amplitude and phase of the incident terahertz wave can be obtained, and a dynamic range of >60 dB demonstrated using time-gated detection.

Applications:

THz spectra of synchrotron irradiated optical fibers. Contract 8/2012, project “Sensor Systems for Secure Operation of Critical Instalation”, funced by UEFISC, in cooperation with European Synchrotron Radiation Facility, Grenoble, (France) in the frame of COST Action TD1205 [1]

THz images of mid-IR optical windows irradiated with alpha particles. Contract 67/2013,, project “Evaluation of Components for Space Applications – ECSA”, funded by Romanian Space Agency - ROSA, in cooperation with IFIN-HH. [2,3]

THz investigation of vegetation water stress. Contract 6, project Drought monitoring based on space and in-situ data – DROMOSISfunded by Romanian Space Agency – ROSA, in cooperation with National Meteorological Administration Romania

Characterization of thin films materials in the frame of our institute collaboration with D. Ghitu Institute of Electronic Engineering and Nanotechnologies, Chisinau – Republic of Moldova

Other Applications:
  • Electronic inspections
  • Food contamination
  • Dental investigation (demineralization of enamel)
  • Pharmaceutical Tablet analysis
  • Solar cells characterization
  • Crystalline content of amorphous samples
  • Polymorph detection and identification, quantification
  • Polymorphic transition
  • Content uniformity
  • Phase transformation with thermal studies (heated cell option required)
  • Art restoration
  • Security applications (explosive detection etc.)

The equipment is of interest for the Romania participation to the COST Actions:

References:

[1]  Sporea D., Mihai, L, Sporea A, Lixandru A, Brauer Krisch E.,  Investigation of UV optical fibers under synchrotron irradiation, Optics Express, vol. 22, Iss. 25, pp. 31473–31485 (2014) , DOI: 10.1364/OE.22.031473

[2] D. Sporea, Adelina Sporea, Laura Mihai, A. Stancalie, The ECSA Project, International Conference “16th International Conference on Transparent Optical Networks - ICTON 2014”, July 7-9, 2014,  Graz, Austria.

[3] D, Sporea, A. Sporea, L. Mihai, A. Stancalie, Test of mid-R components for space missions,  International Conference Mid-IR Optoelectronics, MIOMD 2014, Octomber 5-9 2014, Montpellier, France.