Time-resolved spectroscopy using a chopper wheel as a fast shutter

Abstract

Widely available, small form-factor, fiber-coupled spectrometers typically have a minimum exposure time measured in milliseconds, and thus cannot be used directly for time-resolved measurements at the microsecond level. Spectroscopy at these faster time scales is typically done with an intensified charge coupled device (CCD) system where the image intensifier acts as a "fast" electronic shutter for the slower CCD array. In this paper, we describe simple modifications to a commercially available chopper wheel system to allow it to be used as a "fast" mechanical shutter for gating a fiber-coupled spectrometer to achieve microsecond-scale time-resolved optical measurements of a periodically pulsed light source. With the chopper wheel synchronized to the pulsing of the light source, the time resolution can be set to a small fraction of the pulse period by using a chopper wheel with narrow slots separated by wide spokes. Different methods of synchronizing the chopper wheel and pulsing of the light sources are explored. The capability of the chopper wheel system is illustrated with time-resolved measurements of pulsed plasmas.

Detection of fast electrons in pulsed argon inductively-coupled plasmas using the 420.1–419.8 nm emission line pair

“…Using one emission line for normalization, the model line ratio values are a function Argon emission spectra for 2p emission lines recorded at three different times in a pulsed Ar plasma (1 ms period, 30% duty, 500 W average power). Spectra (corrected for the detector's wavelength sensitivity) were recorded at 1.4 nm resolution using the system described in [24]. only of the electron temperature.…”

“…x y emission lines for three different times in a pulsed plasma: (i) at the start of the power on portion of the pulse, (ii) near the end of the power on portion, and (iii) in the afterglow of the pulse shortly after the power is turned off. In these spectra, recorded with a low-resolution spectrometer system [24], the general dependence of the emission signal on the electron temperature, electron density, and metastable density can be qualitatively characterized by examining the behavior of the ∼751 nm and 763.5 nm peaks (labeled as 'high-E' and 'low-E' respectively in figure 4). The 763.5 nm peak corresponds to emissions out of the 2p 6 level and has a large metastable excitation cross section [46].…”

“…OES measurements are generally more sensitive to the presence of high energy electrons since it requires at least 13 eV of energy to excite a ground state Ar atom into an Ar(3p 5 4p) excited level. For instance, the 750.4 nm (2p → 1 1 s 2 in Paschen's notation) emission line, which is almost always dominated by the ground state excitation process [20], is often used to monitor the behavior of pulsed plasmas [12,13,[21][22][23][24]. Nevertheless, the emission intensity of a single line does not correlate exactly with the electron temperature, since the emission rate is proportional to the product of the electron density and the excitation rate coefficient, both of which are varying during the pulse period.…”

Complex transients in power modulated inductively-coupled chlorine plasmas

“…Emission was collected using optical fibers equipped with collimating lenses on the input side. Time-resolved intensity measurements were achieved with a mechanical chopper that was synchronized with the pulsing frequency of the plasma, as describe in detail elsewhere [23]. The resolution of time-resolved OES was 7% of the pulsed plasma period.…”

A new concept for temporal gating of synchrotron X-ray pulses

“…Few solutions exist that allow the time structure of the X-ray pulse pattern to be changed. The most reliable among them are mechanical choppers (LeGrand et al, 1989;Wulff et ISSN 1600-5775 al., 2002Gembicky & Coppens, 2007;Meents et al, 2009;Kudo et al, 2009;Ito et al, 2009;Husheer et al, 2012;Plogmaker et al, 2012;Wang et al, 2015;Fö rster et al, 2015). Besides many technical challenges, their main disadvantage is the low flexibility of the devices which generally prevents a transfer to another setup.…”