Optogalvanic Research Articles

New Energy Levels of Neutral Lanthanum Derived from an Optogalvanic Spectrum between 5610 and 6110 Å

In a previous paper, we reported on a complete optogalvanic (OG) spectrum of a discharge burning in a La–Ar gas mixture, in the spectral range 5610–6110 Å (17,851 to 16,364 cm−1). Now we are able to communicate further new energy levels, found via searching for laser-induced fluorescence lines when exciting unclassified lines from the OG spectrum. We were able to find 17 new levels, and for two further levels, the line list has extended. With the help of these 19 levels, we could classify 132 spectral lines.

Self-induced optogalvanic effect in a segmented hollow-cathode discharge

Optogalvanic (OG) interaction is simulated and studied in a segmented hollow-cathode discharge (SHCD). HCD-lamps are used to induce an OG signal by their own emission or by that of another lamp. The efficiency of the OG of a Ne/Cu HCD lamp in the range 320-380 nm is estimated theoretically. An irregular galvanic peak arising near the inflection point in the i-V curve (∂V/∂i<0) is detected. Its origin is related to Penning ionization of the sputtered cathode material.

Development of a see-through hollow cathode discharge lamp for (Li/Ne) optogalvanic studies.

Development of a demountable and see-through hollow cathode (HC) discharge lamp suitable for optogalvanic (OG) spectroscopy is described. The design of the HC lamp is simple, compact, and inexpensive. Lithium, investigated rarely by the OG method, is selected for cathode material as its isotopes are important for nuclear industry. The HC lamp is characterized electrically and optically for discharge oscillations free OG effect. Strong OG signals of lithium as well as neon (as buffer gas) are produced precisely upon copper vapor laser pumped tunable dye laser irradiation. The HC lamp is capable of generating a clean OG resonance spectrum in the available dye laser wavelength scanning range (627.5-676 nm) obtained with 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran dye. About 28 resonant OG lines are explicitly observed. Majority of them have been identified using j-l coupling scheme and assigned to the well-known neon transitions. One line that corresponds to wavelength near about 670.80 nm is assigned to lithium and resolved for its fine (2S1/2 → 2P1/2, 3/2) transitions. These OG transitions allow 0.33 cm-1 accuracy and can be used to supplement the OG transition data available from other sources to calibrate the wavelength of a scanning dye laser with precision at atomic levels.

Zeeman structure of red lines of lanthanum observed by laser spectroscopy methods

Laser Induced Fluorescence (LIF) Spectroscopy and Optogalvanic (OG) Spectroscopy were used for the investigation of the Zeeman hyperfine (hf) structures of 27 spectral lines of La I in the wavelength range between 633.86 and 667.54 nm. As a source of free La atoms a hollow cathode discharge lamp was used. Spectra were recorded in the presence of a relatively weak magnetic field (about 800G) produced by a permanent magnet, for two linear polarization directions of the exciting laser beam. As a result of the measurements, we determined for the first time the Landé gJ- factors of 18 levels of La I. The Landé gJ- factors of 12 other levels were re-investigated and determined with higher accuracy.

Wavelength calibration of narrowband ArF laser with iron hollow cathode lamp

Accurate and precise wavelength controlling of narrowband excimer lasers is essential for the lithography of an integrated circuit. High-precision wavelength tuning and calibration of a line-narrowed ArF laser are presented in this work. The laser spectrum is narrowed to a sub-picometer with a line narrowing system. Absolute wavelength calibration of the line-narrowed laser is performed based on the optogalvanic (OG) effect using iron hollow cathode discharge (HCD). An sccuracy of better than 0.1 pm for wavelength tuning and calibration is achieved with our homemade wavemeter.

Nonselective and polarization effects in time-resolved optogalvanic spectroscopy

Three interfering effects in optogalvanic (OG) spectroscopy are identified in a hollow cathode discharge (HCD) - OG detector. The laser beam is found to generate two nonselective processes, namely photoelectron emission (PE) from the cathode surface with a sub-breakdown bias applied, and nonresonant space ionization. The convolution of these galvanic contributions was determined experimentally as an instrumental function and a deconvolution procedure to determine the actual OG signal was developed. Specific plasma conductance is detected dependent on the polarization of the laser beam irradiating. Linearly/circularly polarized light beam is found to induce OG signals differ in amplitude (and their shape parameters in the time-resolved OG signals (TROGS)). The phenomena coherence and specific conductance are found to be in causal relationship. The additional conductance due to coherent states of atoms manifests itself as an intrinsic instrumental property of OG detector.

Long-term wavelength drift compensation of tunable pulsed dye laser for sodium detection lidar

Wavelength stabilization for a pulsed laser presents more challenges than that of continuous wave laser. We have developed a simple and efficient long-term wavelength drifts compensation technique for tunable pulsed dye lasers (PDL) applied in sodium detection lidar system. Wavelength calibration and locking are implemented by using optogalvanic (OG) spectroscopy in a Na hollow cathode lamp (HCL) in conjunction with a digital control software. Optimization of OG signals for better laser wavelength discrimination and feedback control is performed. Test results indicate that locking the multimode broadband PDL to the Na atomic transition corresponding to 589.158nm is well achieved although the temperature in the laboratory is unstable. Through active compensation, the maximum wavelength drift is reduced from over 5pm to 0.42pm in 10h and the maximum wavelength drift rate of the PDL is improved from 3.3pm/h to 0.3pm/h. It has been used to efficient sodium resonance fluorescence lidar detection. This technique is economical and easy to implement, and it provides flexible wavelength control and allows generalization for some other applications which require the wavelength of tunable pulsed lasers to be fixed at an atomic resonance transition references.

Studies on laser-assisted Penning ionization by the optogalvanic effect in Ne/Eu hollow cathode discharge

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.

Studies on pulsed optogalvanic effect in Eu/Ne hollow cathode discharge.

The optogalvanic (OG) effect has been observed in a Eu/Ne hollow cathode discharge lamp using pulsed laser irradiation. An OG spectrum is recorded in dye laser wavelength region 574–602 nm using a boxcar-averager. In total 41 atomic lines are observed. Of these, 38 lines are assigned to neon transitions. Two lines observed corresponding to wavelengths 576.519 and 601.815 nm are assigned to europium transitions; (4f 7 6s 2 , S 8 7/2 →4f 7 6s6p , zP 6 7/2 ) and (4f 7 6s 2 , S 8 7/2 →4f 7 6s6p , zP 8 9/2 ), respectively, and the remaining line at 582.475 nm could not be assigned. The effect of the discharge current on europium as well as neon OG signals is also studied. At moderate discharge current values, an extra positive peak is observed in neon OG signal for the transition (1s 5 →2p 2 ) at 588.189 nm, which is explained by Penning-ionization process using the quasi-resonant energy transfer interactions between excited neon and europium atoms lying in 2p 2 and D 10 9/2 states, respectively.

Laser-induced optogalvanic signal oscillations in miniature neon glow discharge plasma

Laser-induced optogalvanic (OG) signal oscillations detected in miniature neon glow discharge plasma are investigated using a discharge equivalent-circuit model. The damped oscillations in OG signal are generated when a pulsed dye laser is tuned to a specific neon transition (1s5→2p2) at 588.2 nm under the discharge conditions where dynamic resistance changes its sign. Penning ionization via quasi-resonant energy transfer collisions between neon gas atoms in metastable state and sputtered electrode atoms in ground state is discussed to explain the negative differential resistance properties of discharge plasma that are attributed to oscillations in the OG signal. The experimentally observed results are simulated by analyzing the behavior of an equivalent discharge-OG circuit. Good agreement between theoretically calculated and experimental results is observed. It is found that discharge plasma is more sensitive and less stable in close vicinity to dynamic resistance sign inversion, which can be useful for weak-optical-transition OG detection.

Observation of even-parity autoionization states of uranium by three-colour photoionization optogalvanic spectroscopy in U–Ne hollow cathode discharges

Three-colour three-step photoionization spectroscopy of uranium has been performed in a U–Ne hollow cathode discharge tube by temporally resolving three-colour photoionization optogalvanic (PIOG) signal from the normal optogalvanic (OG) signal using three tunable pulsed dye lasers. U–Ne hollow cathode discharge tube has been used as a source of uranium atomic vapours and photoionization detector. Using this technique, photoionization spectra of uranium have been investigated systematically in the energy region 52,150–52,590cm−1, through three different excitation pathways, originating from its ground state, 0cm−1(5Lo6). By analysing the three-colour photoionization spectra sixty new even-parity autoionization resonances of uranium have been identified and their probable total angular momentum (J) values have been assigned according to the J-momentum selection rule. The J-value of five autoionization resonances, which have been observed either through all three excitation pathways or through two different excitation pathways where J-value of the second excited levels differs by two, has been assigned uniquely.

Temporal evolution of two-photon time-resolved optogalvanic signals of neon in the 600–630nm region

Abstract Time-resolved optogalvanic (OG) signals of six two-photon transitions of neon were studied in the 600–630 nm region to 2p54d[5/2]2, 2p54d[3/2]2, 2p54d[3/2]1, 2p54d[1/2]1 and 2p55s′[1/2]1 states from the allowed states of the 2p53s configuration (2p53s[3/2]1 and 2p53s′[1/2]0 states). The OG signals were recorded over a range of discharge currents from 2 to 10 mA. The decay rates of the upper and lower states were obtained by fitting the waveforms with the Han et al.’s mathematical rate equation model considering the three states contributing to the signal. Based on the values of decay rates of the upper states, it was proposed that, after excitation to 5s and 4d states, neon atoms radiatively decay to the lumped relevant electronic states of the 2p53p and 2p54p configurations which have the main contribution in producing the OG signals. It was found that, the decay rates of the upper states (the lumped relevant electronic states of 2p53p and 2p54p configurations) increase linearly and slowly with the discharge current for all the transitions considered in this work. The effective decay rates of the upper states and their electron collisional ionization rate parameters were also obtained. This study showed that the dominant relaxation process in the de-population of the upper states is the lengthened radiative decay in plasma medium after laser excitation.

One and Two-photon Excited Optogalvanic Spectra of Argon in the Wavelength Region of 735 – 850 nm

Optogalvanic (OG) spectra of argon in the visible to near-infrared spectral region between 735 and 850 nm were investigated using a Grimm-style glow-discharge tube, which has been widely used to obtain depth profiles of the elemental composition on various film-like samples. About 49 lines of one-photon and two-photon OG peaks were observed with a pulsed Ti:sapphire laser; these peaks were precisely assigned. Two-photon OG spectra of argon were easily observed without focusing the pulsed laser irradiation to more than 1 mJ. The excitation mechanisms of the observed argon OG spectra could be classified into 3 types: single-photon transition, two-photon transition, and two-photon stepwise transition. In addition, a pseudo-resonant effect was also found to be effective. The argon lines observed in this experiment are suitable as convenient calibration wavelength markers of pulsed tunable laser radiation.

Changes in the Optogalvanic Signal Amplitude in a Hollow Cathode Discharge

The spatial distribution of the optogalvanic (OG) signal in argon at the 801.489 nm (<TEX>$1s_5-2p_8$</TEX> transition at the metastable level in Paschen notation) was investigated in the radial direction of a hollow cathode discharge tube. The results of this experiment showed that the OG signal amplitude decreases in accordance with the following two conditions; first, the level of discharge current and second, the distance from the cathode dark space. These results can be quantified by analyzing the electron density profile along the discharge regions, which can directly influence the collisional ionization induced by electron impact.

Observation of penning ionization in Zr–Ne discharge by optogalvanic effect

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).

Rydberg transitions in neon observed by optogalvanic effect in the 830–870 and 380–420 nm regions

New optogalvanic (OG) Rydberg–Rydberg transitions of neon have been observed in the near-infrared region (830–870 nm), using a commercial Fe–Ne hollow cathode. They involve transitions from the 3d[3/2] J=1 and 3d[7/2] J=3,4 levels to high-lying nf levels. In addition, other OG transitions, observed in the blue range, have been completely assigned to ns, nd, ns′ and nd′ Rydberg series excited from the 3p[1/2] J=1 and 3p[5/2] J=2,3 levels of neon. These transitions and assignments allowed us to extend the range of tunable laser calibration on the two edges of the visible range, where there is a lack of available calibration lines, i.e. the near-infrared and the far-blue range, with a 0.01 nm absolute accuracy.

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.

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.

Direct comparison of electric field measurement byfluorescence and optogalvanic Stark spectroscopies

Electric field in the cathode fall region of a 2.2 Torr heliumdc discharge with 0.8 mA cm-2 current density has beenmeasured from the Stark splittings of 11 1P (unperturbed)Rydberg transition by simultaneous optogalvanic (OG) andfluorescence techniques. The LIF Stark spectra showed narrowerlinewidths compared to the OG spectra for higher parabolicquantum number states; LIF data also showed broader linewidthsfor higher parabolic quantum number states compared to the linesin the centre of the manifold. However, the electric fieldsobtained from the two methods were in agreement with each otherwithin three per cent for all the measured locations in thesheath. A comparison of the OG spectrum with the off-axis LIF datashows a combination of signal gain in the high-field regionalong with the Stark intensity distribution permits the line-of-sight-averaged OG spectrum to obtain accurate field values in adischarge with modest radial field gradients.

Optogalvanic Properties of the Ion Guide Source in the Recoil Nucleus Selective Photoionization

This consideration is a conjunction of two processes: generation of recoil products and selective detection. A new type of plasma is carried out. The electron energy function distribution of the ion-guide source plasma is calculated and discussed. The properties of a laser ionization scheme detecting recoil atoms are analyzed using an optogalvanic approach. The Resonant Laser Ionization (RLI) in low temperature currentless plasma, formed by accelerated particle beam propagating through gas, will be used for the above mentioned separation. A tuned dye laser excites the studied atoms and the fast electrons ionize them. This process exceeds in cross-section the ionization from ground state which provides selectivity of IGS. The latter produces ions of almost all chemical elements. It can be used for investigating processes flowing in low temperature currentless plasma which presents a specific interest. These functions impart to the IGS the role of an Optogalvanic (OG) element, to be precise, of hollow cathode discharge used as an OG detector [1]. In this paper the IGS is analyzed as an OG detector in a quasi OG scheme. The investigation is a step simulating the IGS properties. The Electron Energy Distribution Function (EEDF) and the most important processes are analyzed and discussed as a first step in this field. The results obtained contribute to the efficiency of the RLI method.