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We investigated the self-excited as well as optogalvanically stimulated heartbeat instability in RF discharge complex plasma. Three video cameras measured the motion of the microparticles, the plasma emission, and the laser-induced fluorescence simultaneously. Comprehensive studies of the optogalvanic control of the heartbeat instability revealed that the microparticle suspension can be stabilized by a continuous laser, whereas a modulated laser beam induces the void contraction either transiently or resonantly. The resonance occurred when the laser modulation frequency coincided with the frequency of small breathing oscillations of the microparticle suspension, which are known to be a prerequisite to the heartbeat instability. Based on the experimental results we suggest that the void contraction during the instability is caused by an abrupt void transition from the dim to the bright regime [Pikalev et al., Plasma Sources Sci. Technol. 30, 035014 (2021)]. In the bright regime, a time-averaged electric field at the void boundary heats the electrons causing bright plasma emission inside the void. The dim void has much lower electric field at the boundary and exhibits therefore no emission feature associated with it., 10 pages, 10 figures, supplemental materials

This chapter starts with a brief historical description of the optogalvanic effect and the Joshi effect that eventually led to the technique of optogalvanic spectroscopy (OGS) after the advent of tunable lasers in the mid 1970s. A simple two-state mathematical model of interaction between optical radiation with atoms in the discharge plasma has been used to illustrate the generation of negative and positive voltage OG signals. A variety of experimental arrangements have been discussed for recording the laser optogalvanic spectra (LOGS) of atoms, molecules, and ionic species in dc discharge, hollow cathode discharge, flames, and microwave discharge. Applications of this novel technique in the spectroscopy of short-lived atomic and molecular species in the hostile environment of discharge plasma and flames have been illustrated with suitable examples. The importance of LOGS technique, for ion mobility measurements in flames, ultrasensitive detection capability in intracavity laser experiments, investigation of Rydberg states and negatively charged ionic species, is duly emphasized with appropriate examples.

New Lande- g J factors of 35 energy levels of La I, found from investigations of 40 spectral lines in the wavelength range 562.959÷609.537 nm, were determined. As a source of free La atoms a hollow cathode discharge lamp was used. We monitored the signal of the optogalvanic effect appearing when a laser beam is passing through the hollow cathode. Spectra were recorded in the presence of a magnetic field of about 800 G produced by a permanent magnet, for two linear polarizations of the exciting laser light. Optogalvanic spectroscopy is a very sensitive method, so we were able to observe the Zeeman effect of very weak atomic lines. In this way we have determined for the first time the Lande- g J factors for 35 recently found levels of neutral La. The Lande g J - factors for several other levels were reinvestigated.

The galvanic manifestation of two transformations of degenerate magnetic states of the neon atom, namely self-alignment non-alignment and alignment orientation is studied by monitoring the voltage across the discharge in a range of hollow cathode discharge (HCD) lamps. The application of a magnetic field to the discharge disorders the self-alignment. Alignment and orientation are optically induced and their effect on the discharge conductance is compared by measuring the optogalvanic signals. The degenerate states investigated are found to contribute to the gas discharge conductance in a manner which depends on their degree of coherence. Various hollow cathode discharge media are studied including Ne/As, Ne/Cu, Ne/Ni, Ne/Cd, Ne/Li and Ne/Ca in the corresponding trademarked HCD spectral lamps. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The prospect of finding life outside Earth has fascinated mankind for ages, and new technology continuously pushes the boundary of how remote and how obscure evidence we can find. Employing smaller, or completely new, types of landers and robots, and equipping them with miniature instruments would indeed revolutionize exploration of other planets and moons.In this thesis, microsystems technology is used to create a miniature high-precision isotope-resolving molecular spectrometer utilizing the optogalvanic effect. The heart of the instrument, as well as this thesis, is a microplasma source.The plasma source is a split-ring resonator, chosen for its simplicity, pressure range and easily accessible plasma, and modified to fit the challenging application, e.g., by the adding of an additional ground plane for improved electromagnetic shielding, and the integration of microscopic plasma probes to extract the pristine optogalvanic signal.Plasma sources of this kind have been manufactured in both printed circuit board and alumina, the latter for its chemical inertness and for compatibility with other devices in a total analysis system. From previous studies, classical optogalvanic spectroscopy (OGS), although being very sensitive, is known to suffer from stability and reproducibility issues. In this thesis several studies were conducted to investigate and improve these shortcomings, and to improve the signal-to-noise ratio. Moreover, extensive work was put into understanding the underlying physics of the technique.The plasma sources developed here, are the first ever miniature devices to be used in OGS, and exhibits several benefits compared to traditional solutions. Furthermore, it has been confirmed that OGS scales well with miniaturization. For example, the signal strength does not decrease as the volume is reduced like in regular absorption spectroscopy. Moreover, the stability and reproducibility are greatly increased, in some cases as much as by two orders of magnitude, compared with recent studies made on a classical OGS setup. The signal-to-noise ratio has also been greatly improved, e.g., by enclosing the sample cell and by biasing the plasma. Another benefit of a miniature sample cell is the miniscule amount of sample it requires, which can be important in many applications where only small amounts of sample are available.To conclude: With this work, an important step toward a miniature, yet highly performing, instrument for detection of extraterrestrial life, has been taken.

We have measured the relative transition probabilities of the 1s i –2p j transitions in rare gases using hollow cathode lamps. The emission spectra of each rare gas were recorded as a function of discharge current. Two independent calibration modes for the spectrometer have been used to increase the reliability of our data. Uncertainty in the data have been measured and found to be within ~5%. The relative transition probabilities are reported for 30 lines of Ne I, 25 lines of Ar I, fourteen lines of Kr I, and eighteen lines of Xe I. The present results are in good agreement with the published data. The data can also be used to calibrate the relative detection efficiency of a spectrometer over a range of 400–1000 nm.

This paper presents novel observations on inverse optogalvanic effect in Yb transition at 679.9 nm ( 3 P 1 → 3 S 1 ) in contrast with the observed normal optogalvanic effect at 648.9 nm ( 3 P 0 → 3 S 1 ) transition and Penning ionization in Yb-Ne mixture by probing Ne transitions at 626.65 (1s 3 →2p 5 ), 633.44 (1s 5 →2p 8 ), 650.65 (1s 4 →2p 8 ) and 659.89 nm (1s 2 →2p 2 ) in Yb-Ne hollow cathode lamp. These conclusions are derived by studying the optogalvanic signals temporal profile probed by DCM dye based narrow line-width ~2 GHz, short pulse ~20 ns, high repetition rate 5.0 kHz tunable dye laser, as a function of discharge current. The observed inverse optogalvanic effect is attributed to the transfer of Yb population in the level 3 P 0 through radiative decay from the upper level 3 S 1 of the transition. This proposition is confirmed by recording the emission spectra of Yb-Ne hollow cathode lamp. The Penning ionization signature in Ne optogalvanic signals is due to the quasi-resonances between Yb and Ne energy levels. Penning signature observed in optogalvanic signal of Ne transition at 650.65 nm is unique and attributed to the increase in concentration of Ne metastable level 1s 5 through radiative decay from the 2p 8 level.

Intracavity optogalvanic detection of 14C utilizes the narrow band specificity of 14CO2 laser resonances in the infrared spectrum, coupled with greatly enhanced sensitivity from amplified effective path lengths in optical cavities. Background (nonresonant) interactions are also enhanced in such cavities, making proper separation of signals from background imperative. Intracavity Optogalvanic Spectroscopy (ICOGS) is similar to cavity ring-down spectroscopy (CRDS) with certain crucial differences. An ICOGS model, based on a basic CO2 laser and optogalvanic effect physics, is presented. Experimental results using a laboratory instrument with a continuous flow of small CO2 samples in a buffer gas illustrate the model. It is shown that acquisition of optimized signal-to-background ratios for the quantitation of 14CO2 in samples of order 10 μg is achievable, considerably smaller than with CRDS.

Using neon hollow cathode lamp and employing laser optogalvanic technique, we have studied population redistribution in the 2p 5 3p multiplet. The spectra recorded in the laser energy region of 23300 cm − 1 –23600 cm − 1 show transitions originating from both the laser excited levels as well as from an adjacent level whose population builds up as a result of collisional deactivation. Employing the optical delay technique, we have been able to extract decay rates associated with the collisional population mixing of the p levels.

The pulsed optogalvanic (OG) effect is used to observe Penning ionization in a Zr–Ne hollow-cathode discharge, which was axially irradiated by a pulsed dye laser pumped by copper vapor laser. The effect of discharge current on the temporal evolution of the OG signal is studied at 588.2, 594.5, 597.6 and 614.3 nm. The double humped temporal profile of the OG signals, corresponding to transitions of neon, and closeness of energy levels between that level of neon (Ne) and excited levels of zirconium (Zr) ions confirmed that Penning type of ionizing energy transfer collisions were taking place in the Zr–Ne discharge at lower discharge currents (≤5 mA). The disappearance of the double humped feature in the temporal profile of the OG signals indicated that the Penning contribution became negligible at higher discharge currents (≥10 mA).

Time dependent optogalvanic signals induced by the 1s 4 → 2p j laser excitations have been studied in neon DC plasma. The decay rates related to all the four 1s i levels have been derived by fitting the waveforms with a mathematical rate equation model. The temporal signatures of three transitions namely 638.3, 650.7 and 724.5 nm related to the 2p 7 , 2p 8 and 2p 10 upper levels, respectively, have been found to be different from the rest of the transitions. We relate these effects to the population redistribution of decaying channels and to the processes responsible for the optogalvanic effect.

The Lamb dip of CO rovibrational transition is detected by a room temperature extracavity RF optogalvanic cell and employed to stabilize the frequency of a CO laser. The S/N ratio of optogalvanic signal is about 2000 $\mathrm{Hz}^{-\frac{1}{2}}$ at optical power < 1 W. The relative depth of Lamb dip is 2.3%. The S/N ratios of first and third harmonic demodulated saturation signals are about 40 $\mathrm{Hz}^{-\frac{1}{2}}$ and 10 $\mathrm{Hz}^{-\frac{1}{2}}$ , respectively. The CO laser is stabilized using the first harmonic demodulated signal, and the frequency stability is better than 300 kHz. Concurrently, the influences of operational parameters, which include the coil current, partial pressures of gas mixture, are investigated. A simple model for the influence of coil current is presented, and further improvements are addressed as well.

We report on the temporal evolution of the optogalvanic signals in neon using a commercial hollow cathode lamp in conjunction with a Nd:YAG pumped dye laser system. We have recorded transitions excited from each of the neon 1s states over a range of discharge current to investigate the dominant physical processes responsible for the optogalvanic effect in neon discharges. The decay rates associated with the four 1s levels have been obtained using a mathematical rate equation model. A linear relationship between the decay rates and the discharge current has been found and the effective lifetimes and the electron collisional rate parameters of the 1s levels have been determined.

A strong optogalvanic effect has been observed in a negative glow of a miniature neon discharge lamp using tunable pulse dye laser pumped by a copper vapor laser. A comparative study on temporal evolution of optogalvanic signal in a positive and negative dynamic resistance region of the discharge is described. Dye laser beam was tuned to various neon transitions 1s i → 2p j (Paschen notations) within 570–617 nm wavelength range. Anomalous behavior of optogalvanic signal was observed at 588.2 nm for (1s 5 → 2p 2 ) neon transition at low discharge current ( V /d i 5 ) and electrode sputtered atoms in ground state using their partial energy level diagram.

In this work time resolved optogalvanic signals associated with transitions excited from the first metastable state of neon and krypton have been studied. These gases have similar energy state configurations and it is of significant interest to study their time resolved optogalvanic waveforms resulting from transitions belonging to the states of same quantum numbers. The experimentally observed optogalvanic signals recorded for different discharge currents have been fitted to a theoretical model to obtain parameters that determine amplitudes, instrumental time constants and decay rates of the 1s levels. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Accelerator mass spectrometry (AMS) has been developed over the past 25 years as an effective method to count 14C atoms. An alternative 14C measurement technique, suitable for routine laboratory use, combining the optogalvanic effect with laser assisted isotope ratio analysis (LARA) is now being extended from its current use for precision analysis of 13CO2 to similar analysis of 14CO2. The analyzer uses a unique resonance between a specific molecular transition in the molecule 14CO2 and the narrow band output of a laser based on the same molecular transition. Isobaric background is not an issue as in AMS, and the sample is not consumed in analysis so that long averaging times with small samples is possible.

Laser-assisted Penning ionization (LAPI) is detected in a Ne/Eu hollow cathode (HC) discharge lamp using the pulsed optogalvanic (OG) method. In the Ne/Eu discharge, doubly ionized europium excited energy levels Eu[4f(7)(P(7/2,5/2)6)] lie within the thermal limit (∼kT) from the laser-excited neon's energy level [2p(5)(P3/202)3p or 2p(8) (in Paschen notation)] lying at 149,848 cm(-1). Therefore, Penning ionization (PI) of europium atoms likely to occur into its highly excited ionic states is investigated. To probe the PI of europium, the temporal profiles of its counterpart neon OG signal are studied as a function of discharge current for the transitions (1s(4)→2p(8)) and (1s(2)→2p(2)), corresponding to 650.65 and 659.89 nm wavelengths, respectively. It is observed that PI of europium alters the overall discharge characteristics significantly and, hence, modifies the temporal profile of the OG signals accordingly. The quasi-resonant ionizing energy transfer collisions between laser-excited Ne 2p(8) atoms and electronically excited europium P(9/2)10 atoms are used to explain the LAPI mechanism. Such LAPI studies carried out in HC discharge could be useful for the discharge of a metal-vapor laser with appropriate Penning mixtures.

We measured the optogalvanic signal and discharge voltage-current(V-I) curve under the two different discharge conditions with different buffer gases, Ar, and Ne. When the Gd was used as a cathode material at low discharge current less than 10mA, a significant change was observed in the current-voltage curve. Time resolved optogalvanic signal measurement were measured by the diode laser of which wavelengths correspond to metastable transition line of these gases (Ar, Ne). From these measurements, we found that the characteristics of the V-I curve strongly depend on the Penning ionization process.

Three light-induced galvanic contributions to the real optogalvanic (OG) signal were studied in a hollow cathode discharge (HCD). The photoelectron emission (PE) from the cathode surface with a sub-breakdown bias applied, and hence no discharge present, was measured within the framework of an OG experimental arrangement. The PE component in a real OG measurement was found to manifest itself as an instrumental effect along with the effect of nonresonant ionization. The convolution of these components was determined experimentally as an instrumental function, and a deconvolution procedure to determine the actual OG signal was developed. The transient characteristics of the OG circuit were analysed by time-deconvolution of the measured OG signal, and they turned out to be dependent on the operating HCD I–V point. In addition, the polarization of the light beam irradiating the HCD was found to influence the OG signal.

The plasma temperature of Ar gas in hollow cathode discharge were measured. This is done by measuring the line profile of the 1s/sub 8/-2p/sub 8/ transition in Ar, using a single-frequency diode laser. Low power diode lasers have been successfully used for investigation of the line profiles of Ar transitions in hollow cathode discharges. It turns out that the plasma temperature of Ar is 640∼783 K in the discharge current range at 7∼10 mA.

Fluorescence from neutral atomic yttrium is measured at the 2D°5/2 → 2D3/2 transition, corresponding to a wavelength of 622.26 nm. The upper level, 2D°5/2, is excited using a diode laser operated in an extended cavity Littrow's configuration at 643.5 nm, corresponding to the 2D5/2 → 2D°5/2 transition. The atomic source is a hollow cathode lamp. A concurrent optogalvanic signal has also been measured.

The dynamic behavior of the optogalvanic effect in neon hollow cathode discharge using continuous wave diode laser is described. The optogalvanic signal can be subdivided into two types, which show characteristic difference in the metastable atomic density. The polarity and the magnitude of peak of the optogalvanic signal has close relation to change of the lowest metastable atom density.

When a laser is tuned between two excited energy levels of a gas in a Direct Current discharge lamp, the discharge current will experience a temporary disturbance lasting tens or hundreds of microseconds known as the optogalvanic effect. We have carried out extensive studies of optogalvanic effects in neon discharge plasmas for transitions at 621.7 nm, 630.5 nm, 638.3 nm, 650.7 nm and 659.9 nm. A nonlinear least-squares Monte Carlo technique has been used to determine the relevant amplitude coefficients, decay rates and the instrumental time constant. We discovered an abrupt change in the neon discharge plasma at a discharge current of about 6 mA.