Optogalvanic Signal Research Articles

On the Time‐Resolved Optogalvanic Spectra of Neon and Krypton

AbstractIn 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)

Experimental Improvement of Signal of a Single Laser-CooledTrapped 40Ca+ Ion

A single 40Ca+ ion is loaded in a miniature Paul trap andthe probability of directly loading a single ion is above 50%. Thesignal-to-noise ratio and the storage time for a single ion have beenimproved by minimizing the ion micromotion and locking a 397 nm coolinglaser to a Fabry–Perot interferometer and optogalvanic signal. Fromthe fluorescence spectrum, the ion temperature is estimated to be about5 mK.

Stabilization of the 397 nm and 866 nm external cavity diode lasers for cooling a single calcium ion

The linewidth of a 397 nm laser was narrowed below 1 MHz by locking it to a Fabry-Perot interferometer. In addition, the cavity length of the interferometer was referenced to the Optogalvanic signal of calcium ions. The long-term drift of the laser frequency was reduced below 10 MHz over 2 h. This frequency stabilization was also applied to an 866 nm laser. With such lasers, we can achieve better signals from a single calcium ion confined in a miniature Paul trap.

Doppler-free Stark spectroscopy of the second excited level of atomic hydrogen for measurements of electric fields

The Stark splitting of the second excited level of atomic hydrogen (with principal quantum number $n=3$) has been measured by pulsed laser spectroscopy in order to determine small electric fields by optical means. Doppler-free excitation with two counterpropagating laser beams at $205\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ allows us to measure the $n=3$ Stark spectra either by an optogalvanic signal after ionization by a third laser photon or by detection of the Balmer-$\ensuremath{\alpha}$ fluorescence photons emitted by the excited atoms. Three different cases of laser polarization have been investigated in order to evaluate the possibilities and limitations of this one-step laser excitation method for electric field determination, especially at field strengths below $200\phantom{\rule{0.3em}{0ex}}\mathrm{V}∕\mathrm{cm}$. The method provides the best field sensitivity achieved with lower excited levels that can be reached directly by two-photon absorption from the ground state (in contrast to the more sensitive Rydberg levels). For this purpose, an advanced tunable pulsed uv laser with narrow bandwidth almost at the Fourier limit has been used. The high spectral resolution allowed us to deduce electric field strengths as small as $50\phantom{\rule{0.3em}{0ex}}\mathrm{V}∕\mathrm{cm}$ from the frequency shift between two selected isolated Stark components. As a main advantage, this simple analysis of the measured spectra does not rely on knowledge of the line intensities which may be strongly affected by the measuring conditions.

속이 빈 원통형음극 방전의 전압-전류 곡선에서 음 저항 영역 관찰

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.

The study of dominant physical processes in the time-resolved optogalvanic spectra of neon

We present the dominant physical processes responsible for the production of the optogalvanic signal in the spectra of neon. We have investigated the effects on the optogalvanic signal by scanning a dye laser across the neon transitions in the DC discharge plasma. Time-resolved spectra are obtained at a fixed wavelength of the dye laser resonantly tuned to an optically allowed transition. The temporal evolutions of the signals are registered on a storage oscilloscope. Three transitions from the 3s[1/2]2 metastable state corresponding to the ΔJ = ΔK = 0, ±1 dipole selection rules have been selected to investigate the dominant physical processes responsible for the optogalvanic signals. The change in the signal amplitude as a function of the discharge current has been registered. In addition the electron collisional ionization rate parameter ratios have been determined for the transitions corresponding to dipole selection rules ΔJ = ΔK = -1, ΔJ = ΔK = 1 and ΔJ = ΔK = 0, as 1.63, 1.75 and 1.0 respectively. The effective lifetimes of the upper levels involved in the aforementioned transitions are also calculated as 62.5 μs, 31.25 μs and 12.85 μs respectively.

Instrumental contributions to the time-resolved optogalvanic signal in a hollow cathode discharge

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.

Fluorescence and optogalvanic signals in atomic yttrium from tunable diode laser excitation in a hollow cathode lamp

Fluorescence from neutral atomic yttrium is measured at the 2D° 5/2 → 2D 3/2 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 2D 5/2 → 2D° 5/2 transition. The atomic source is a hollow cathode lamp. A concurrent optogalvanic signal has also been measured.

The Optogalvanic Line Shapes of Neon Transitions in a Hollow Cathode Discharge Tube

The optogalvanic line shapes are observed in a commercial hollow cathode discharge tube containing neon buffer gas. Anomalous optogalvanic line shape is particular for transition originating from the 3P 2 (1S 5 in Paschen notation) metastable level of neon. The anomalous line shape is interpreted as being due to two competing atomic processes, which are the collisional ionization and the depletion of metastable atoms. When the competition is almost comparable at discharge current of 15 mA, the differences in the polarity and the magnitude of the optogalvanic signal of the transition result in the anomalous line shape.

Temporal evolution and variation of laser optogalvanic signals in the spectra of inert gases

We present new studies on the temporal evolution and variation of the laser optogalvanic signals in the spectra of inert gases using commercial hollow cathode lamps in conjunction with a Nd:YAG pumped dye laser system. The behavior of the optogalvanic signals for the transitions following the ΔJ=ΔK=0 and ± 1 dipole selection rules in the jcK-coupling scheme namely mp5(m+1)p[5/2]3, mp5(m+1)p′[3/2]2, mp5(m+1)p[3/2]2, mp5(m+1)p′[1/2]1 and mp5(m+1)p[1/2]1 coupled with mp5(m+1)s[3/2]2 (m=2, 3, 4 and 5 for neon, argon, krypton and xenon, respectively) metastable level have been investigated. An empirical relation is formulated: S(t)=Smin+A(t)exp(−α[I−I0]) which satisfactorily describes the shift of the optogalvanic signal and the change in the population of the upper level as a function of the discharge current. It is observed that the shift in the optogalvanic signal peaks for the ΔJ=ΔK=−1 transitions is larger than that for the ΔJ=ΔK=+1 transitions whereas the signal peaks remain unshifted for the ΔJ=ΔK=0 transitions.

Collisional dynamics of the first excited states of neon in the 590-670 nm region using laser optogalvanic spectroscopy

A mathematical rate equation model, incorporating the various processes contributing to the generation of optogalvanic signals in a discharge plasma, has been used to analyze the time-resolved waveforms of neon in the wavelength region 590–670 nm. Amplitudes, decay rates and the appropriate instrumental time constant have been determined using a non-linear least-squares fit of the observed time-resolved optogalvanic waveforms.

Temporal evolution and variation of laser optogalvanic signals in the spectra of inert gases

We present new studies on the temporal evolution and variation of the laser optogalvanic signals in the spectra of inert gases using commercial hollow cathode lamps in conjunction with a Nd:YAG pumped dye laser system. The behavior of the optogalvanic signals for the transitions following the Δ J=Δ K=0 and ± 1 dipole selection rules in the j cK-coupling scheme namely mp 5( m+1)p[5/2] 3, mp 5( m+1)p ′[3/2] 2, mp 5( m+1)p[3/2] 2, mp 5( m+1)p ′[1/2] 1 and mp 5( m+1)p[1/2] 1 coupled with mp 5( m+1)s[3/2] 2 ( m=2, 3, 4 and 5 for neon, argon, krypton and xenon, respectively) metastable level have been investigated. An empirical relation is formulated: S( t)= S min+ A( t)exp(− α[ I− I 0]) which satisfactorily describes the shift of the optogalvanic signal and the change in the population of the upper level as a function of the discharge current. It is observed that the shift in the optogalvanic signal peaks for the Δ J=Δ K=−1 transitions is larger than that for the Δ J=Δ K=+1 transitions whereas the signal peaks remain unshifted for the Δ J=Δ K=0 transitions.

Collisional dynamics of the first excited states of neon in the 590-670 nm region using laser optogalvanic spectroscopy

A mathematical rate equation model, incorporating the various processes contributing to the generation of optogalvanic signals in a discharge plasma, has been used to analyze the time-resolved waveforms of neon in the wavelength region 590–670 nm. Amplitudes, decay rates and the appropriate instrumental time constant have been determined using a non-linear least-squares fit of the observed time-resolved optogalvanic waveforms.

Optogalvanic spectroscopy of silicon atoms

The laser cooling transition of silicon atoms was observed in a discharge with a hollow cathode containing silicon using the third harmonic coherent light of a nanosecond Ti:sapphire laser. The optogalvanic spectrum obtained was investigated by scanning the wavelength of the coherent light from 250.3 nm to 253.3 nm. Four lines originating from the 3s 23p 2 3P → 3s 23p4s 3P 0 transition of silicon atoms were observed in the spectrum, while the spectral resolution was limited to 0.1 nm by the linewidth of the coherent light. Optogalvanic signals increased in intensity as the discharge current decreased. This spectroscopic technique will help us to address the accurate frequency of the light source for the laser cooling of silicon atoms.

Study of Even-Parity Autoionization States of Samarium Atom by Laser Optogalvanic Spectroscopy

Two-color two-step laser resonance ionization spectroscopy (RIS) was used to study autoionization states of neutral samarium atom (Sm I). Optogalvanic signals were detected from a Sm hollow cathode lamp which was used as an atomic source. Several metastable states of the ground state term were populated from the heated hollow cathode. The six intermediate states which had mutually different total angular momentum ( J ) values from 1 to 6 were excited using the first step dye laser from the ground state ( J =0) and three metastable states having J values of 3, 4 and 5. These six excitation channels were used to study systematically the autoionization states having the probable J values from 0 to 7. The 359 even-parity autoionization states were found and their J values were estimated. The 357 states among the 359 autoionization states were newly found in this experiment.

The Role of Metastable Atoms for Optogalvanic Signal Generation in a Neon Negative Glow Discharge

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.

Optogalvanic effect sign change of the 667.8 nm He line in a hollow cathode discharge plasma

The optogalvanic signals (OGS) at the 667.8 nm He line are investigated with low power diode lasers in a longitudinal hollow cathode discharge tube in pure He and in a He:Ne=1:1 gas mixture. A simple model for explaining the dependence of the OGS signal amplitude and sign on pressure is applied. The values obtained for the pressure where the OGS sign changes in pure He are in good agreement with the model calculations. A qualitative explanation of the zero point dependence on current is made. An explanation of the decrease of the OGS in a He:Ne=1:1 mixture discharge is proposed.

Light-induced conductivity in Ar/Al hollow cathode discharge through ArII (4s–4p) transitions and secondary electrons generation

The opto-galvanic signal (OGS) induced through ArII (4s–4p) transitions in Ar/Al hollow cathode discharge (HCD) is studied. The signal is found influenced by Penning's process. The light-induced ionization is calculated as a negligible contribution to the conductivity. The γ-process of ion-secondary electrons generation in HCD is analyzed related to the ionic OGS. The later is ascribed to the light-induced intensification of ion→secondary electron production based on the higher potential energy of the photoexcited Ar + ion.

THE DYNAMIC OPTOGALVANIC SIGNAL IN HOLLOW CATHODE DISCHARGE AS A SPECTRAL AND MONITORING INDICATOR

Four optogalvanic (OG) measuring specific solutions are developed. They are based on the OG effect, in particular on the sensitivity of the OG signal form to the operating point. This form changes with each variation of gas discharge conditions. A transformation of the Dynamic OG signal in quasi-amplitude one is reported. All of the solutions represent a fast and more sensitive method for atomic line diagnostics. The optogalvanic analogue of the AC EL-spectrum is investigated in a inverted OG scheme.

Study of Odd-Parity Autoionization States of Praseodymium Atom by Optogalvanic Spectroscopy

Autoionization states of neutral praseodymium atom (Pr I) were investigated using two-color two-step laser resonance ionization spectroscopy (RIS). A Pr hollow cathode lamp was used as an atomic source and optogalvanic signals were measured. The Pr I was excited from the ground state to four first step excitation levels (21120.69, 21471.81, 22014.11 and 23067.34 cm -1 ) by the first step laser. These four channels were used to study odd-parity autoionization states. Four dyes were used in the second step excitation. The 108 odd-parity autoionization states were found by optogalvanic spectroscopy and their total angular momentum ( J ) values were estimated.