Free space Terahertz Emitter

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Features

  • Based on LT-GaAs or GaBiAs photoconductive material
  • Optimized for wavelengths around 800 nm or 1060 nm
  • Wide spectral range and low noise
  • Sub-picosecond temporal resolution
  • Technical passport and test report included

Applications

  • Time-resolved broadband THz spectroscopy
  • Optical pump - THz probe spectroscopy
  • THz imaging

Principle of Operation

THz emitter consists of a microstrip photoconductive antenna (PCA) fabricated on GaAs substrate. Depending on pump laser wavelength either low temperature grown GaAs (LT-GaAs) or GaBiAs is used as photoconductor. On its surface a coplanar Hertzian type dipole antenna structure is formed using AuGeNi metallization. Photoconductive antenna geometry, as well as the properties of photoconductor 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 laser with 30 mW output power and <150 fs pulse duration.

THz emitter is illuminated by laser beam from panel side. Laser beams must be focused between two electrodes (Fig. 1). The gap between metallic contacts is larger than the laser spot. THz radiation is collected by integrated lens, manufactured from high-resistivity silicon (HRFZ-Si), mounted on X-Y stage (Fig. 2). TERAVIL offers two standard types of these lenses: for collimated or diverging THz beam output. In second case PCA is placed in aplanatic point of silicon lens, which reduces THz beam spherical aberrations. Adjustment screws are used for Si lens positioning onto PCA center. SMA sockets on back side of the housing are used for connecting DC or AC bias to THz emitter. Any of three M6 holes can be used for THz emitter mounting on optical table (Fig.3).

Fig 1. Microstrip antenna drawing

  

Fig 2. THz emitter crossection


Fig 3. THz emitter/detector housing

Specifications


Emitter Model EMT-8 EMT-10
Photoconductive Antenna
Photoconductive material LT-GaAs GaBiAs
Dimensions of the wafer 5 x 1.5 mm
Thickness 600 µm
Antenna type strip line dipole
Bias voltage 50 V max, 40 V typical
Central THz frequency ~0.5 THz
Integrated focusing lens
Material HRFZ-silicon
Geometrical form hyper-hemi-sphere
THz beam output collimated or diverging
X-Y adjustable stage range ±3 mm
Pump beam parameters
Excitation wavelength 800±40 nm 1060±40 nm
Average power <50 mW <20 mW
Pulse duration <150 fs
Pulse repetition rate 20-100 MHz
Beam profile near to Gaussian
Beam diameter ~2 mm

Fig 4. EMT-8 (LT-GaAs) THz emitter radiated power* dependance on bias voltage and laser excitation power

  

Fig 5. EMT-10 (GaBiAs) THz emitter radiated power* dependance on bias voltage and laser excitation power

*Measured using TYDEX Optoacustic detector GC-1P (Gollay Cell).



Fig 6. THz emitter mounted on standard optics holder

Ordering Information


Description Model Notes
THz emitter for 800 nm wavelength EMT-8 Includes Si lens and coaxial cable with BNC connector
THz emitter for 1060 nm wavelength EMT-10 Includes Si lens and coaxial cable with BNC connector
THz emitter/detector mounting stage MNT Includes pump beam focusing lens on XYZ stage
TMS-100M bias power supply TMS-100 30 - 70 V DC or square-wave output