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Real -time Terahertz Spectrometer

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Features

Wide spectral range up to 3.5 THz (116 cm^-1)
Excellent spectral resolution better than 5 GHz (0.17 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

Applications

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 broad-band spectral coverage and high dynamic range.The system is designed with two delay lines: fast and slow. Fast scan line allows real time data acqui-sition with 10 spectra/sec. speed. Averaging up to 1064 samples can increase signal to noise ratio to 10⁶:1 at 0.4. Additional slow delay line extends scan window from 110 ps to 220 ps; as a result system obtains excellent spectral resolution of Δf < 5 GHz. The fast scan line is designed without bearings and uses a magnetically coupled drive which makes it extremely reliable and signi-f cantly extends the lifetime. Our 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. Because THz waves penetrate dielectric materials like paper or plastic, are reflectedby materials with free electrons like metals and are absorbed by molecules with certain vibration levels within the terahertz band, they have a lot of applications in the felds of time-domain spectroscopy and imaging. Terahertz absorption or refection spectroscopy, imaging of biological and other objects, THz tomography, and ultrafast 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.

Fig.1. Example of THz-TDS exeriment

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.

Fig.2. typical performance of Real-time THz spectrometer (measured in ambient atmosphere) - THz pulse waveform and Fourier-transform spectra. (Click on the picture to enlarge)

Examples of THz spectra

Fig.3. Absorption coefficient measurements of RDX and PETN in ambient atmosphere. (Click on the image to enlarge).

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 150 fs pulse duration. FWHM bandwidth of detection system exceeds 700 GHz, with usable spectral range of 0.1–3.5 THz.

Fig. 4. THz radiation emitter and detector

Software

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 1064 spectra to increase dynamic range. Raw data can be exported to file for further analysis.

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 confgurations are available, optimized for transmission, reflection,imaging or pump-probe measurement. All can be easily interchanged and modified.Any other optional configurationcan be ordered initially or as a future upgrade.

Basic THz Spectroscopy Kit includes:

photoconductive antenna,
THz emitter and detector,
pump laser beam guiding optics,
motorized slow delay line with controller,
THz beam guiding mirrors,
sample holder,
lock-in amplifie,
Labview based software for data acquisition.

Optionally:

femtosecond laser,
purging box,
personal computer.

Requests for custom-made version are welcome.