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TOPAG Lasertechnik GmbH
Nieder-Ramstädter Str. 247
64285 Darmstadt
Telefon: +49 6151 4259 78
Telefax: +49 6151 4259 88 
E- mail: info [at] 

T-SPEC Spectrometer

T-SPEC Terahertz Spectrometer


The Real-Time Terahertz spectrometer T-SPEC is a complete system for measurements with pulsed THz radiation and allows reflectivity, absorption and transmission measurements as well as imaging and pump-probe experiments in the frequency range from 0.1 to 3.5 THz (3-116 cm-1). The fast scan line is designed magnetically coupled without bearings which makes it extremely reliable and ensures long lifetime.


Bezeichnungen der Tabs

  • Description
  • Specifications
  • Pictures
Tab 1


  • Wide spectral range up to 3.5 THz (116 cm-1)
  • Excellent spectral resolution better than 2.5 GHz (0.08 cm-1)
  • High power S/N ratio >106:1 at 0.4 THz
  • Real-time data acquisition up to 10 spectra/s
  • “No bearing” design of fast delay line – virtually unlimited lifetime
  • Transmission and reflection modes
  • High spatial resolution THz imaging
  • Complete PC control
  • User-friendly software for transmission or/and absorption measurements, imaging


  • THz transmission, reflection spectroscopy
  • Optical pump – THz probe spectroscopy
  • Chemical material characterization
  • Medical and biological nondestructive research
  • Semiconductor wafer inspection
  • Polymeric compounding
  • Explosives detection
  • Your application is welcome…

Real-Time Terahertz Spectrometer

offered by EKSPLA is a powerful tool for investigative applications of pulsed terahertz waves. With simple and robust design, it is easy-to-use and adaptable to individual requirements. The unique design of microstrip photoconductive antenna fabricated on low-temperature grown GaAs (LT-GaAs) substrate ensures broadband spectral coverage and high dynamic range. The system is designed with two delay lines: fast and slow. Fast scan line allows real time data acquisition with 10 spectra/sec. speed. Average of collected spectra can increase signal to noise ratio to 106:1 at 0.4 THz. Additional slow delay line extends scan window from 110 ps to 440 ps; as a result system obtains excellent spectral resolution of Δf < 2.5 GHz. The fast scan line is designed without bearings and uses a magnetically coupled drive which makes it extremely reliable and significantly extends the lifetime. Our T-SPEC series spectrometer is the perfect choice for broadband THz imaging. It allows scan of up to 25×25 mm sample with spatial resolution of approx. 1 mm. Measurements contain information about the target, revealing both structural and spectroscopic information.

Basic operation principles of THz Time Domain Spectroscopy

The terahertz (THz) and sub-THz frequency region (100 GHz – 10 THz) of the electromagnetic spectrum bridges the gap between the microwaves and infrared. THz waves penetrate dielectric materials like paper or plastic, are reflected by materials with free electrons like metals and are absorbed by molecules with certain vibration levels within the terahertz band. Terahertz absorption or reflection spectroscopy, imaging of biological and other objects, THz tomography, and optical pump-THz probe spectroscopy are all hot topics in recent scientific conferences with possible applications in semiconductor, medical and security industries.The typical THz Time Domain Spectroscopy (THz-TDS) setup is shown in Fig. 1

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Fig. 1: Example of THz-TDS experiment

Sub-picosecond 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.

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Fig. 2a: Typical performance of T-SPEC series real-time THz Spectrometer (measured in ambient atmosphere) - THz pulse waveform

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Fig. 2b: Typical performance of T-SPEC series real-time THz Spectrometer (measured in ambient atmosphere) - Fourier-transform spectra.

Examples of THz spectra

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Fig. 3a: Absorption coefficient measurements of RDX in ambient atmosphere.

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Fig. 3b: Absorption coefficient measurements of PETN in ambient atmosphere.

THz Components

The key components for any THz system are THz radiation emitter and detector. EKSPLA THz emitter and detector features a microstrip photoconductive antenna fabricated on low-temperature grown GaAs (LT-GaAs) substrate. THz radiation is collected and collimated by integrated hemispherical high‑resistivity silicon lens, mounted on X-Y stage. Performance of photoconductive antenna, depends on carriers mobility and their trapping time in semiconductor layers. LT-GaAs is one of the best materials for THz applications because of its high carrier mobility, fast carrier capture time, high breakdown voltage and high resistivity. LT-GaAs growth technology allows controlling the photoexcited carrier lifetime within a very wide region: from less than 100 fs to 100 ps. Photoconductor antenna geometry, silicon lens parameters, as well as the properties of LT-GaAs epitaxial layers were optimized for highest THz radiation output efficiency while preserving optimal bandwidth.

As a result, the typical emitted THz radiation power exceeds several μW when pumped by mode-locked ultrafast laser with 30 mW output power and 100 fs pulse duration. FWHM bandwidth of detection system exceeds 700 GHz, with usable spectral range of 0.1–3.5 THz. Versions for different types of pump lasers are available.

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Fig. 4: THz radiation emitter and detector


Stand-alone software is supplied with the device. It has integrated tools for complete system control, transmission/ absorption spectra analysis, 2D imaging data visualization and spectral analysis by X, Y position. It also allows real-time signal and spectra monitoring (useful for system adjustment) as well as averaging up to 1024 spectra to increase dynamic range. Raw data can be exported to file for further analysis.

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Fig. 5: Software main window (image of blade (size 97 x 97 pixels) acquired in imaging mode at 1 THz frequency).

Build Your own THz spectrometer

As a totally flexible and cost effective solution, Ekspla offers the Terahertz Spectroscopy Kit. Four standard configurations are available, optimized for transmission, reflection, imaging or pump-probe measurement. All can be easily interchanged and modified. Any other optional configuration can be ordered initially or as a future upgrade. Basic THz Spectroscopy Kit includes:

  • THz emitter and detector,
  • pump laser beam guiding optics,
  • motorized slow delay line with controller,
  • THz beam guiding mirrors,
  • sample holder,
  • lock-in amplifier,
  • Labview based software for data acquisition.
  • femtosecond laser,
  • purging box, removes water absorption lines,
  • personal computer.
Requests for custom-made version are welcome.
Tab 2
ModelT-SPEC series real-time THz SpectrometerTHz Spectroscopy Kit
General specifications
Spectral range 3-116 cm-1 (0.1-3.5 THz) 6-100 cm-1 (0.2-3 THz)
Power signal to noise ratio
at 0.4 THz > 106:1 3) > 106:1
at 1 THz > 105:1 3) > 105:1
at 2 THz > 103:1 3) > 103:1
Power signal to noise ratio (real-time scan) 4)
at 0.4 THz 750:1 -
at 1 THz 100:1 -
Spectral resolution
slow scan - < 15 GHz (0.5 cm-1)
fast scan < 10 GHz (0.33 cm-13) -
combined mode (fast+slow) < 2.5 GHz (0.08 cm-1) -
Scan range 110 ps / 440 ps 5) 300 ps 6)
Pump laser requirements
Output power > 60 mW
Pulse duration 50-150 fs 1)
Wavelength 760-840 nm
Pulse repetition rate 20-100 MHz 2)

1) 20 fs version available

2) Inquire for other pulse repetition rates

3) For 256 spectra averaging in fast scan mode (measurement time ~30 sec. )

4) Up to 10 spectra/sec.

5) In fast scan mode/in combined mode (fast + slow)

6) Inquire for longer scan ranges


Reflectance measurement option Allows measurement of reflected spectra
20 fs pump version Allows to use shorter than 50 fs optical pulse for emiter and detector pump

Requests for custom-made versions are welcome!

Tab 3

Tab 3 Inhalt

Tab 4

Tab 4 Inhalt

Tab 5
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Beschreibung 1
T-SPEC series real-time terahertz spectrometer 
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Beschreibung 2
Example of THz-TDS experiment 
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Beschreibung 3
Typical performance of T-SPEC series real-time THz Spectrometer (measured in ambient atmosphere) - THz pulse waveform 
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Beschreibung 4
Typical performance of T-SPEC series real-time THz Spectrometer (measured in ambient atmosphere) - Fourier-transform spectra. 
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Beschreibung 5
Absorption coefficient measurements of RDX in ambient atmosphere. 
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Beschreibung 6
Absorption coefficient measurements of PETN in ambient atmosphere. 
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Beschreibung 7
THz radiation emitter and detector 
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Beschreibung 8
Software main window (image of blade (size 97 x 97 pixels) acquired in imaging mode at 1 THz frequency). 
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Beschreibung 9
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Beschreibung 10
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