January 15, 2024

Researchers from Germany have developed and demonstrated a new diagnostic technique for obtaining local distribution of gas phase hydrogen peroxide (H2O2) in plasma jets. Continuous-wave cavity ringdown spectroscopy, with a quantum cascade laser at a wavelength of 8.12 μm, is used to determine the effective absorption length of a cold atmospheric pressure plasma jet and to determine the localized density of H2O2 in the effluent of the plasma jet. With axial and radial scans and radial distributions, the effective absorption length was calculated to be 1.6 mm close to the nozzle and 5 mm at a distance of 10 mm from the nozzle.

The maximum density of H2O2 was found in the center of the effluent close to the nozzle. This work shows the formation and consumption mechanisms of H2O2 and enables other biomedically relevant species in the plasma zone to be studied using this technique.

Measuring the localized density of H2O2 with high-accuracy requires high precision and stable control of the quantum cascade laser when using continuous-wave cavity ringdown spectroscopy (cw-CRDS). Wavelength Electronics’ QCL driver, QCL1000 OEM, enabled precise current control with minimal electronic noise from the QCL. As laser linewidth is a major concern for QCLs, the QCL1000 OEM minimizes noise for open air measurements to as low as 0.7 μA up to 100kHz as well as keeping the average current noise density to as low as 2 nA / √Hz.

The stability of the QCL temperature is also critical for consistent wavelength output from the QCL. Wavelengths’ PTC5K-CH temperature controller, can precisely stabilize temperature to as low as 0.0012ºC. The PTC utilizes a PI controller to minimize overshoot and time to reach setpoint temperature. The stability that the QCL driver and PTC controller provided for the QCL made the 3,600 repeatable measurements more reliable.

The complete case study is available as CS-LDTC13.

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