Laser optogalvanic spectroscopy of an indium atom

The specific features of the optogalvanic effect in a hollow-cathode discharge on single- and two-stage excitation of indium atoms are studied. The autoionized states of an indium atom in the region 52,651–52,500 cm⁻¹ have been revealed and investigated by means of the method of optogalvanic spectroscopy. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 396–398, May–June, 2000.     

Application of Diode Lasers to Determine Excitation Temperature in Hollow Cathode Discharges by Optogalvanic Spectroscopy

The excitation temperatures of sputtered gadolinium and uranium atoms in an argon hollow cathode discharge have been determined by diode laser-excited optogalvanic spectroscopy. These results have been compared to those determined by conventional emission spectroscopy. It was found that the temperatures derived from each method do not differ very much, but the optogalvanic method revealed a better standard deviation uncertainty due to the good signal-to-background ratios and excellent spectral resolutions. Temperature variations with discharge currents ranging from 15 to 50 mA have been examined.     

A method to measure electric field strengths in an argon glowdischarge plasma using laser spectroscopy

A method for electric field measurement based on laser spectroscopy of argon atoms has been developed and calibrated. Measurements were made using both laser optogalvanic spectroscopy and laser-induced fluorescence spectroscopy. Measurements using several different transitions in argon were carried out, and it was found that the 4s→7f and 4s→8f transitions were the most suitable for measurements in the sheath region of glow discharges. The lower limit for electric field measurements was estimated to be 500 V/cm. A minimal pressure of about 100 mtorr was required to detect optogalvanic signals and about 1 torr was required for the fluorescence signals to be detectable. These detection limits make this method applicable for measurement of sheath electric fields for a wide range of discharge conditions     

Noncontact optogalvanic signal detection in DC discharge CO<Subscript>2</Subscript> lasers

A new noncontact method for detecting optogalvanic signals in DC discharge CO₂ lasers is reported. The presented technique is based on the detection of potential difference variations through a capacitor comprised of a discharge plasma column and a coaxial or parallel conductor. The obtained optogalvanic signals exhibit better responsivity and pulse shape in comparison with other conventional techniques; in addition, they are detectable as far as 3 m from a signal source.     

The theory of the optogalvanic effect in metal vapour-rare gas discharges

A theory of the laser-excited optogalvanic effect in metal vapour-rare gas discharges is elaborated. The metal vapour depletion due to the ionization processes and the energy losses from the plasma caused by the ion and electron flux to the wall and the elastic and inelastic collisions between electrons and atoms are taken into account. The metal atom depletion increases if the discharge current or the intensity of the laser radiation are increased. The more complete energy balance leads to a substantially greater optogalvanic signal than obtained from previous theories. The metal atom depletion, however, appreciably decreases the optogalvanic signal except very small discharge currents.     

Optogalvanic spectroscopy of sputtered atoms

Optogalvanic Spectroscopy (OGS) is finding wide ranging applications in atomic structure studies, laser wavelength calibration, intensity and frequency stabilization of lasers and analytical chemistry. Sputtered atoms produced in a hollow cathode lamp by the bombardment of a rare gas discharge is a convenient source for optogalvanic spectroscopy work. Here, we discuss the sputtered ion/atom optogalvanic spectroscopy applications to low resolution atomic spectroscopy, laser wavelength calibration, studies of radioactive samples available in limited quantities, studies of atoms in highly excited states and Rydberg atoms and high resolution laser spectroscopy. For the sake of completeness, we list other applications of OGS without going into details.     

Intermodulated optogalvanic Zeeman spectroscopy in a hollow cathode discharge

The Zeeman and hyperfine structures of various transitions of calcium, copper, and neon are investigated by means of Doppler-free optogalvanic spectroscopy. This work demonstrates the suitability of the hollow cathode discharge to high resolution Zeeman spectroscopy of refractory and reactive elements.     

Relationship of the laser-induced population perturbation of excited levels with the dynamical optogalvanic signal in a discharge plasma

For a pulsed-laser excitation of various neon transitions (1s_j → 2p_k) in a glow discharge the population perturbations in the upper and lower levels are measured by emission and absorption spectroscopy, and the dynamical optogalvanic signals are observed. We propose that the population perturbation in the lower levels (1s₂–1s₅) as a whole is responsible for the optogalvanic signal, and that metastable-level populations determine its decay characteristics. The sign reversal of the optogalvanic signal that depends on the excitation condition is interpreted in this context.     

用脉冲电场光电流光谱研究Ne原子的自电离态

本文用脉冲电场光电流光谱的实验方法测定Ne原子ns＇(n=15—31)和nd＇(n=13—30)两通道的35条自电离态能级,用参数拟合得出Ne原子ns＇和nd＇通道的电离阈值,计算了每条能级的量子亏损,实验用脉冲电场代替直流放电,基本上消除了Stark效应在光电流光谱测量中的影响。 关键词：     

Optogalvanic detection as a quantitative method in spectroscopy

The use of the optogalvanic effect for measuring spectroscopic quantities such as wavelengths, line profiles and line integrals is discussed. The quantitative aspects of absorption and optogalvanic spectroscopy are compared. It is experimentally demonstrated for calcium that optogalvanic line integral measurements are not simply linearly related to the oscillator strength. Measured optogalvanic and absorption profiles for Ne, Ar and Cu are compared and it is shown that both methods yield the same result for certain conditions of the observed plasma. The dependence of the optogalvanic profiles on the current in the plasma is demonstrated.     

Spatial Dependence of the Strong Optogalvanic Effects Due to Metastable Quenching in a DC Helium Discharge

The optogalvanic effects of the He 2.058-?m line (21P-21S) from He lamps illuminating a weak dc He discharge (current density ?10 ?A/cm2, field/pressure ~25 V/cm - torr) are reported. For illumination at the positive column, we have made quantitative measurements of the decreases in the discharge current, electron density, and metastable densities, as weli as the increase in the electric field in the positive column, as the intensity of illumination increases. We have also observed that for sufficiently strong illumination (using He lamps only), the optogalvanic effect is catastrophic, i.e., the discharge is switched off; this clearly shows that a sufficiently large metastable density (which is reduced by the illumination) is necessary to maintain a weak He discharge. For illumination at the cathode regions, the optogalvanic effects are "anomalous": the discharge current is strongly suppressed by illumination at the cathode dark space next to the cathode, but is enhanced by iumination at the adjacent negtive glow region.     

运用光电流光谱测定钬原子能级的超精细结构

用自制钬空心阴极灯,运用光电流光谱技术在569nm～600nm谱区内首次测定了元素钬的9条谱线,确定其相应跃迁能级,及超精细结构常数.     

铥原子激发能级超精细结构常数的测定

用铥空心阴极灯,采用光电流光谱技术测得铥原子21条一级跃迁谱线,确定了相应跃迁上能级的超精细结构常数,其中7个能级的参数为首次发表,运用同一空心阴极灯,采用双色双光子级联共振技术,由荧光法首次测得4个第二激发能级的超精细结构常数.     

Chopped CW laser-induced optogalvanic effect in a neon hollow cathode discharge

A detailed model for the optogalvanic effect in a neon hollow cathode discharge irradiated by a chopped CW dye laser is presented. A rate equation formalism is used to calculate the evolution of the first and second electronic configuration populations coupled by the laser and of the electric charges number density. Processes as ambipolar-like electrons loss, electronic collisional coupling of level populations and electron emission by the cathode due to VUV radiation from the 1s ₂ resonant level are taken into account and further discussed.The transients and steady-state magnitude of the optogalvanic signal are calculated, compared with experimental data and related to population changes. We predict sign changes of the optogalvanic signal when the laser is tuned over transitions originating from the resonant level with respect to transitions involving the metastables states. The optogalvanic signal is shown to be basically determined by the laser-induced variations of the excited-state populations while changes in the electron temperature, due to laser energy transfer by collisions between electrons and excited atoms, play a negligible role.     

对汞亚稳态瞬态特性的研究

本文报道用脉冲光电流效应对Hg原子在低压放电中亚稳态6³P_0.2和第一共振态6³P₁衰减机制的研究。指出亚稳态原子间的碰撞电离、再复合及二极扩散过程是这种缓慢衰减的主要因素。实验测定了在不同温度下6³P_0,1,2态的平均有效寿命及扩散系数。实验结果与理论计算相符。由于6³P_0,1,2态在Hg放电中的关键作用,这种灵敏、简便和干扰小的 关键词：     

Optogalvanic Effects in a Hollow Cathode Discharge at Irradiation with its Original Spectrum

An evaluation is made and some experiments are carried out which prove the possibility of optogalvanic effect appearing in experiments using hollow cathode discharge not only when one hollow cathode discharge is irradiated by another but also in the simplest possibly experimental scheme where only one hollow cathode discharge plays simultaneously the role of an emitter and an irradiator.     

Optogalvanic detection of velocity-selective optical pumping in an open, cascade atomic medium

We performed two-color spectroscopy of the (4s²) ¹S₀ → (4s4p) ¹P₁ → (4p²) ¹D₂ calcium atomic transition and observed velocity-selective optical pumping in a calcium hollow cathode lamp by means of optogalvanic detection. The optical pumping signature in optogalvanic detection is compared to that of fluorescence and transmission detections. The optogalvanic technique is found to be a very sensitive method of detecting optical pumping and could be used in distinguishing optical pumping from electromagnetically induced transparency.     

The thermionic double-diode,an efficient detector in excited state laser spectroscopy

We are describing the thermionic double-diode which is a suitable instrument for excited state laser spectroscopy. In comparison to the optogalvanic technique the signal-to-noise ratio was found to be 10²?10³ times better, investigating transitions between excited Sr or Ba states. Combined with its high detection sensitivity the thermionic double-diode presents the possibility of investigating transitions between high angular momentum states. It is demonstrated by studying transitions between Rydberg levels and doubly-excited autoionizing states in Ba. Further advantages are (i) the small strength of the dc electric field and the low electron density in the laser excitation region of the double-diode commending itself for studies of Doppler-free transitions to highly excited states and (ii) the very stable working conditions allowing to vary the pressure and current conditions in the diode in a much wider range than in a discharge.     

Infrared optogalvanic spectroscopy in the helium positive column using an F-center laser

Using optogalvanic spectroscopy with a tunable cw F-center laser, we have detected helium transitions from the n=4 to the n=6 states between 2.61 μm and 2.7 μm. The observed sensitivity is in agreement with the predictions of a steady state model of the positive column discharge.     

Optoacoustic investigation of the mechanisms in the infrared optogalvanic effect

Simultaneous observations of the optogalvanic and optoacoustic effects were performed in CO₂, NH₃ and SF₆ discharges under irradiation by resonant infrared 10 μm laser radiation. The dependence of the galvanic and acoustic signals on the discharge current, and their time evolution following a switch of the laser radiation were investigated. The observations proved that the infrared optogalvanic effect occurs through two different mechanisms, a gas kinetic temperature dependence of the discharge parameters and a modification of the pion production through the vibrational molecular excitation.