Features

• Photoconductive antenna THz emitter and detector

• Build-in hyper-spherical high-resistivity silicon lens

• 0.1–3 THz spectral range

• Sub-picosecond temporal resolution

Applications

• THz time domain spectroscopy

• THz imaging

• Optical pump-THz probe spectroscopy

Introduction

The terahertz (THz) and sub-THz frequency region (100 GHz – 10 THz)   of the electromagnetic spectrum bridges the gap between the microwaves   and infrared. The “THz gap” is attractive because of many possible   applications of terahertz radiation: absorption or reflection   spectroscopy, imaging of biological and other objects, THz tomography,   ultrafast pump-probe spectroscopy.
Ekspla introduces the main building blocks for any THz system – THz   emitter and detector. THz emitter and/or THz detector consists of a   microstrip photoconductive antenna fabricated on low-temperature grown   GaAs (LT-GaAs) substrate pumped by ultrafast laser with shorter than 150   fs pulse duration. THz radiation is collected and collimated by   integrated Si lens, mounted on X-Y stage. Photoconductive antenna   geometry, parameters of the Si lens, as well as the properties of   LT-GaAs epitaxial layers are optimized for highest THz radiation output   efficiency while preserving optimal bandwidth. As a result, typical   emitted THz radiation power exceeds 10 µW when pumped by mode-locked   Ti:S laser with 100 mW output power and 150 fs pulse duration. FWHM   bandwidth of detection system exceeds  700 GHz with usable spectral   range of 0.1–3 THz.

THz imaging

THz radiation has an ability to penetrate deep into many organics
materials, which makes THz imaging attractive for imaging of   biological samples. Image of the sample can be obtained by   raster-scanning of
the sample trough the focused THz beam. Sub-millimeter resolution was reported in scientific literature.

THz Time Domain Spectroscopy

Fig. 1. THz time domain spectrosopy optical layout
The most typical application of THz emitter and detector is THz   Time Domain Spectroscopy (THz-TDS). THz-TDS setup is shown in Fig. 1.   Subpicosecond pulses of THz radiation are detected
after propagation through a sample and an identical length of a   free space. A comparison of the Fourier transforms of these pulse shapes   gives the absorption spectra of the sample under investigation.

Pump-Probe THz Experiments

Femtosecond lasers let to investigate ultrafast nonequilibrium   dynamics in semiconductors. For this aim, optical-pump-optical-probe   techniques are usually employed. In such experiments, an intense optical   pump pulse is used to excite free carriers in a sample, while a weaker   probe beam monitors changes in its optical properties. In contrary to   the optical probe, terahertz probe pulses are non-resonant with the band   gap of semiconductor under investigation and, because of this, can be   used as direct probes of free-carrier dynamics avoiding numerous   experimental artefacts typical for optical-pump-optical-probe systems.

THz Spectroscopy Kit

Our “THz spectroscopy kit” contains all the components necessary to   build THz-TDS system. The standard kit consists of photoconductive   antenna THz emitter and detector, pump laser beam guiding optics,   motorized delay line and bias power supply, THz beam guiding mirrors,   sample holder and lock-in amplifier. All the components are assembled   and tested on the baseplate of 60×80 cm dimensions. The configuration of   the kit can be easily modified, for example, sample holder can be   mounted on motorized X-Y stage for imaging experiments.

Fig. 2. THz pulse waveform (a) and spectrum (b)
Typical examples of data collected are shown in Fig. 2. The THz   pulse waveform and its Fourier spectrum were measured without sample   inserted between emitter and detector in ambient air or argon   atmosphere. The distance between emitter and detector is 30 cm.
Requests for custom-made version are welcome!