Continuous wave cavity ring down spectroscopy measurements of velocity distribution functions of argon ions in a helicon plasma

Thakur, Saikat Chakraborty; McCarren, Dustin; Carr, Jerry; Scime, Earl

doi:10.1063/1.3687429

Cited by 6 publications

(4 citation statements)

References 34 publications

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“…The CRDS technique, developed by O'Keefe and Deacon, is based on the measurement of the absorption rate of a light pulse confined within a closed optical cavity [17]. It is a very sensitive diagnostic technique developed to measure the density of particles present in trace amounts [18,19], e.g. negative hydrogen ion in the present case.…”

Section: Crdsmentioning

confidence: 99%

Characterization of hydrogen plasma in a permanent ring magnet based helicon plasma source for negative ion source research

Pandey¹,

Mukherjee²,

Bandyopadhyay³

et al. 2019

Plasma Phys. Control. Fusion

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HELicon Experiment for Negative ion source (HELEN-I) with single driver is developed with a focus on the production of negative hydrogen ions. In the Helicon wave heated plasmas, very high plasma densities (~10 !" !! ) can be attained with electron temperatures as low as ~ 1 eV in the downstream region. These conditions favor the production of negative hydrogen ions. In HELEN-I device at IPR, helicon plasma is produced using Hydrogen gas in a diverging magnetic field, created by a permanent ring magnet. RF Power (P RF ) of 800-1000W at 13.56 MHz frequency is applied to a Nagoya-III antenna to excite m = 1 helicon mode in the plasma. The plasma is confined by a multi-cusp field configuration in the expansion chamber. The transition from inductively coupled mode to Helicon mode is observed near P RF ~ 700W with plasma density ~ 10 18 m -3 and electron temperature ~ 5 eV in the driver and ~ 1eV in the expansion volume. Line integrated negative hydrogen ion density is measured in the expansion chamber by employing an Optical Emission Spectroscopy (OES) diagnostic technique using ! / ! ratio and Laser photo-detachment based Cavity Ring Down spectroscopic (CRDS) diagnostic technique. The measured value of negative hydrogen ion density is in the order of 10 16 m -3 at 6 mTorr pressure and does not vary significantly with power in the helicon mode, pressure and downstream axial magnetic field variation. The negative ion density measurements are compared with theoretically estimated values calculated using particle balance method considering different reaction rates responsible for negative hydrogen ion creation and destruction. It is to be noted that at present Caesium (Cs) is not injected in the plasma discharge to enhance ! ion density.In surface process, H-ion are produced on a low work-function surface due to surface conversion of energetic H atoms (H 0 * ) or hydrogen ions (H n + ) in the plasma [9];

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Section: Crdsmentioning

confidence: 99%

Characterization of hydrogen plasma in a permanent ring magnet based helicon plasma source for negative ion source research

Pandey¹,

Mukherjee²,

Bandyopadhyay³

et al. 2019

Plasma Phys. Control. Fusion

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“…CRDS overcomes the limitations of the three techniques and has been applied to measure OH radicals in several types of LTPs [13][14][15][16][17][18][19][20]. In addition to OH radicals, several other plasma-generated species involved in plasma processes under various conditions have also been measured by CRDS [21][22][23][24][25][26]. However, when it comes to the complex settings of LTP, e.g.…”

Section: Introductionmentioning

confidence: 99%

Brewster angle-cavity ringdown spectroscopy for low temperature plasma measurements in multiphases

Wang

2023

Plasma Sources Sci. Technol.

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We report on the development of a Brewster angle-cavity ringdown spectroscopy (BA-CRDS) system for low temperature plasma diagnostics. The system can measure gas species in solutions, with a detection limit (minimum detectable absorbance) of 9.1×10-5, which is equivalent to a detection limit of 0.04 parts per billion for measuring OH radicals in water at 308 nm. With higher reflectivity ringdown mirrors and improved designs of a Brewster angle cell, the detection limit can be potentially up to 10-6 or lower. In this exploratory study, absorption cross sections of HgBr2 and H2O2 in aqueous phase at 256 nm are measured to be (1.8±0.1)×10-18 cm2 and (5.2±0.5)×10-20 cm2, respectively. Furthermore, temporal profiles of absorbance from distilled water, HgBr2, and H2O2 solutions when interacting with a helium atmospheric plasma jet are individually characterized at different plasma powers, gas flow rates, and/or solute concentrations. The observed linear temporal profiles of absorbance from the plasma-interacted water suggest formation of H2O2 from plasma-generated OH radicals, while the nonlinear temporal profiles from the plasma-treated HgBr2 solutions reveal possible removal of HgBr2 by OH radicals. Our result demonstrates that the new BA-CRDS system is a powerful tool for quantification of reactive plasma species in multiphases or other complex settings.

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“…For example, Romanini et al 8 used a threshold comparator circuit based on Anderson et al 11 using comparator integrated circuits. Thakur et al 12 used a comparator and 555 timer circuit to control the AOM. Other studies have developed software-based triggers, but they require a fast algorithm and a dedicated digital-to-analog output port on the PC oscilloscope greatly increasing the cost of the system.…”

mentioning

confidence: 99%

“…12 Also, the pulse generator could be triggered directly from the PMT output eliminating the need for a comparator. However, this would require a relatively high signal from the PMT large enough to trigger the switch on the pulse generator (in this case a TTL signal >2 V).…”

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Note: A latched comparator circuit for triggering continuous-wave cavity ring-down spectroscopy

Rasheed

Curtis

2013

Review of Scientific Instruments

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Continuous-wave cavity ring-down spectroscopy offers several advantages over cavity ring-down spectroscopy with a pulsed laser, such as a higher repetition rate and decreased cost. However, the continuous-wave technique requires a more complicated experimental setup because the laser must be switched off rapidly when the intensity is high in order to observe a ring-down event. This note describes an inexpensive and simple latched comparator circuit that can be used to detect light intensity above a threshold value and send a signal to rapidly steer the beam out of the cavity and initiate a ring-down event. The latch eliminates switching noise by preventing the comparator from switching during the ring-down event. © 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4811846] Cavity ring-down spectroscopy (CRDS), first developed by O'Keefe and Deacon, 1 has become increasingly used to measure the absorption and extinction properties of gases, suspended aerosol particles, and liquids. CRDS measures the decay lifetime of photons in an optical cavity composed of highly reflective mirrors. Because the mirrors are highly reflective, the path length of the light in the cavity is typically on the order of kilometers for a cavity with a length of approximately one meter, resulting in very high sensitivity. CRDS has been reviewed extensively in the literature 2-7 and its principles will only briefly be discussed here.Continuous-wave cavity ring-down spectroscopy (CW-CRDS) using a diode laser, developed by Romanini et al., 8 offers several advantages over the initially developed CRDS using a pulsed laser. 7-9 In general, CW-CRDS uses a less expensive and smaller continuous-wave (CW) laser and offers faster sampling rates leading to a more sensitive measurement. Continuous-wave lasers have a more narrow linewidth than pulsed lasers (typically much more narrow than the cavity free spectral range) and the wavelength of some CW lasers can be scanned across a small wavelength range allowing spectral information to be measured. However, CW-CRDS has several disadvantages when compared to pulsed laser CRDS. 7 Most notably, the experimental setup for CW-CRDS is more complicated requiring a method to quickly turn off the laser in order to observe the ring-down event. Commonly, an acousto-optic modulator (AOM) is used to steer the beam into the cavity. When the AOM is triggered off, the beam rapidly steers away from the cavity allowing the intensity of light in the cavity to decay and the ring-down event to be observed.Most CW-CRDS systems use mode-matching lenses 10 to trigger the AOM when the Gaussian TEM 00 transverse mode of the cavity is matched to the laser and the intensity exiting the cavity is highest. Overlap of the laser mode and cavity a)

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Continuous wave cavity ring down spectroscopy measurements of velocity distribution functions of argon ions in a helicon plasma

Cited by 6 publications

References 34 publications

Characterization of hydrogen plasma in a permanent ring magnet based helicon plasma source for negative ion source research

Characterization of hydrogen plasma in a permanent ring magnet based helicon plasma source for negative ion source research

Brewster angle-cavity ringdown spectroscopy for low temperature plasma measurements in multiphases

Note: A latched comparator circuit for triggering continuous-wave cavity ring-down spectroscopy

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