Leibniz Institute for Plasma Science and Technology
Felix-Hausdorff-Str. 2
17489 Greifswald
welcomeatinp-greifswald [punkt] de

The Leibniz Institute for Plasma Science and Technology (INP) is the largest non-university institute in the field of low temperature plasmas, their basics and technical applications in Europe. The institute carries out research and development from idea to prototype. The topics focus on the needs of the market. At present, plasmas for materials and energy as well as for environment and health are the focus of interest.

Cite Dataset

Validation of THz absorption spectroscopy by a comparison with ps-TALIF measurements of atomic oxygen densities

This data set contains the data shown in the corresponding publication in Applied Physics Letters ( This publication presents a benchmark of THz absorption spectroscopy against a more established method. Atomic oxygen densities were measured with THz absorption spectroscopy and compared to those obtained from picosecond (ps) two-photon absorption laser induced fluorescence (TALIF) measurements on the same capacitively coupled radio frequency oxygen discharge. Similar changes in the atomic oxygen density were observed with both diagnostics when varying the applied power (20–100 W) and the gas pressure (0.7–1.3 mbar). Quantitatively, the results are in good agreement as well, especially when considering the total margin of error of the two diagnostics. This shows that THz absorption spectroscopy is an accurate technique that can be reliably used for real-world applications to determine atomic oxygen densities in plasmas.

Release Date
Permanent Identifier (DOI)
Permanent Identifier (URI)
Is supplementing
Plasma Source Name
Plasma Source Application
Plasma Source Specification
Plasma Source Properties

An asymmetric capacitively coupled radio frequency discharge was investigated. The planar RF electrode was made of stainless steel and had a diameter of 120 mm. It was powered at 13.56 MHz by an RF generator (Advanced Energy, Cesar 133) and an automatic matching network (Advanced Energy, Navio). The RF electrode was positioned at a distance of 55 mm beneath the top surface of the grounded reactor vessel, which consisted of aluminum and was cylindrically shaped, with a diameter of 240 mm and a height of 105 mm. The applied RF power was varied between 20 and 100 W.

Plasma Source Procedure
The reactor outlet was connected to a turbopump system (Welch-Ilmvac, CDK 263) with a throttle valve to constantly adjust the pressure in the chamber.
Plasma Medium Name
Plasma Medium Properties

Pure O2 was used as a working gas, at a pressure of 0.7 or 1.3 mbar, and a flow rate of 45 or 50 sccm, respectively. Oxygen gas was let into the reactor by a mass flow controller (MFC) (MKS 1179A with control unit MKS PR4000) at a flow rate of 45 or 50 sccm, respectively.

Plasma Diagnostics Name
Plasma Diagnostics Procedure

Absolute densities of ground-state atomic oxygen were measured with THz absorption spectroscopy, using the fine structure transition of atomic oxygen at 4.74477749 THz (i.e. 158.268741 cm-1). A tunable THz QCL in continuous-wave mode was used as the radiation source. It was operated in a Stirling cryocooler (Ricor K535) at a temperature of 44.30 K. Temperature fluctuations were minimized to be below 5 mK by an additional temperature controller (Stanford Research Systems, CTC100). Tuning of the laser output was achieved by linearly ramping the input current. The current was supplied by a laser driver (Wavelength Electronics, QCL1000 OEM), which was controlled by a function generator (Tektronix, AFG3022C) to provide sawtooth waveforms with a frequency of 11 Hz. After passing through the plasma reactor, the laser radiation was detected by a helium-cooled bolometer (Infrared Laboratories, 4.2K Bolometer). The detected signals were recorded with a digital sampling oscilloscope (R&S, RTO 1014).

Absolute densities of ground-state atomic oxygen were derived from picosecond (ps) two-photon absorption laser induced fluorescence (TALIF) measurements after a calibration using xenon. Photons with a wavelength of approximately 226 nm were provided by a ps laser system that consisted of an Nd:YLF pump laser (EKSPLA, PL3140), a harmonic generator (EKSPLA, APL2100), and an optical parametric generator (EKSLPA, PG411). The fluorescent radiation was detected by a streak camera (HAMAMATSU, C10910-05), which was synchronized with the laser pulses (repetition rate: 5 Hz) by a delay generator (Stanford Research, DG645) and connected to a digital CMOS camera for readout (HAMAMATSU, ORCA-Flash4.0 V3). The streak camera images were recorded using a time range of 200 ns, full gain, and a total acquisition time of 200 s, which corresponds to an accumulation of 1000 laser shots.

Public Access Level
Contact Name
Jente Wubs
Contact Email