Color center laser optogalvanic spectroscopy of lithium,barium, neon and argon Rydberg states in hollow cathode discharges

Numerous infrared transitions between Rydberg states of neon and argon have been measured by optogalvanic spectroscopy in commercial hollow cathode lamps using a color center laser operating in the range 3600–4100 cm^-1. Transitions in lithium and barium atoms sputtered from the cathodes were also detected. The generality and high sensitivity of this technique indicates potential applications for frequency calibration in the infrared, atomic and molecular spectroscopy, and plasma diagnostics.     

A simple method for the optogalvanic detection of argon ion transitions in hollow-cathode lamps

Summary We describe a simple method for the observation of argon ion transitions in hollow-cathode lamps, using the optogalvanic effect, and report the first optogalvanic detection of the six ArII transitions: 457.9 nm, 476.5 nm, 488.0 nm, 496.5 nm, 501.7 nm and 514.5 nm. We also study the optogalvanic signal as a function of the incident laser power and the lamp current. Partial financial support of CNPq and FINEP (Brazil).     

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.     

Hyperfine structure in the atomic spectrum of niobium

We report on hyperfine structure measurements in 21 lines of atomic niobium in the spectral region from 640 nm to 870 nm by means of optogalvanic laser spectroscopy and laser induced fluorescence spectroscopy using a hollow cathode discharge and a tunable single-mode cw ring laser. Hyperfine structure constants A and B of altogether 29 excited energy levels were determined, 18 of them for the first time. Received 18 July 2002 / Received in final form 8 November 2002 Published online 4 February 2003 RID="a" ID="a"e-mail: sk@kalium.physik.tu-berlin.de     

Resolution enhancement of pHe+ atomic line profiles measured with a pulsed dye laser and a Fizeau wavelength meter

A Fizeau wavelength meter was used to compensate for fluctuations in the longitudinal mode structure and wavelength of a pulsed dye laser. The average laser linewidth was effectively narrowed by selection of laser pulses with a single longitudinal mode. These techniques were recently employed to measure some atomic transition wavelengths in pHe+ to fractional precisions greater than 1 part in 10(7). The wavelengths were absolutely calibrated against iodine or tellurium lines by absorption spectroscopy or against neon or argon lines by optogalvanic spectroscopy.     

Application of X‐ray fluorescence to turbulent mixing

Combined measurements of X‐ray absorption and fluorescence have been performed in jets of pure and diluted argon gas to demonstrate the feasibility of using X‐ray fluorescence to study turbulent mixing. Measurements show a strong correspondence between the absorption and fluorescence measurements for high argon concentration. For lower argon concentration, fluorescence provides a much more robust measurement than absorption. The measurements agree well with the accepted behavior of turbulent jets.     

Further experimental investigation of the hyperfine structure in the spectrum of atomic niobium

Laser spectroscopy with either optogalvanic or laser induced fluorescence detection have been employed to measure the hyperfine structure of 25 transitions of atomic niobium in the visible and near infrared spectral range. The magnetic dipole hyperfine interaction constants A of 43 energy levels (22 of even and 21 of odd parity) were determined, 30 of which have been investigated for the first time. The values obtained for the even parity levels are compared with the results of a parametric analysis.     

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：     

Doppler-free optogalvanic spectroscopy using an infrared color center laser

We have used a cw color center laser near 2.6 μm to study highly excited states in helium and neon atoms by Doppler- free intermodulated optogalvanic spectroscopy in a hollow cathode discharge tube. For helium n = 4 to 6 transitions, the resolution was limited to about 320 MHz (FWHM) by Holtzmark broadening due to the presence of charged particles in the discharge. Lines as narrow as 60 MHz were observed for neon 3s₅-5p₁₀.     

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.     

Infrared laser optogalvanic spectroscopy of molecules: Doppler free and double resonance effects

The use of CO₂ and N₂O lasers extends the range of applicability of the infrared laser optogalvanic spectroscopy of molecules recently demonstrated by Webster and Menzies. Doppler free spectroscopy increases the resolution by a factor of about 20 and microwave double resonance enables to observe rotational transitions with extremely small absorption length.     

半绝缘GaAs的双调制反射光谱研究

半导体材料电子能带结构的确定对研究其物理性质及其在半导体器件方面的应用有重要意义.光调制反射光谱是一种无损和高灵敏度的表征半导体材料电子能带结构的光学手段.光调制反射光谱中激光调制导致的材料介电函数的变化在联合态密度奇点附近表现得更为明显.通过测量这些变化,可以得到有关材料能带结构临界点的信息.然而在传统的单调制反射光谱中,激光调制信号的光谱线型拟合和临界点数目的分析往往被瑞利散射和荧光信号所干扰.本文将双调制技术与双通道锁相放大器结合,消除了瑞利信号和荧光信号的干扰,获得了具有较高信噪比的调制反射光谱信号.双通道锁相放大器可以同时解调出反射光谱信号及其经泵浦激光调制后的细微变化量,避免了多次采集时可能存在的系统误差.利用这种技术,在可见激光(2.33 eV)泵浦下,我们测量了半绝缘GaAs体材料从近红外至紫外波段(1.1-6.0 eV)的双调制反射光谱,获得了多个能带结构临界点的信息.探测到了高于泵浦能量之上的与GaAs能带结构高阶临界点对应的特征光谱信号,说明带隙以上高阶临界点的光调制反射光谱本质是光生载流子对内建电场的调制,并不是来自该临界点附近的能带填充效应.这一结果表明双调制反射光谱能够对半导体材料能带结构带隙及其带隙以上临界点进行更准确的表征.     

Optogalvanic detection of 7s-nP transitions in cesium

Using a single frequency ring laser with styryl-9 in the wavelength region 790 to 890 nm, optogalvanic signals of the 7s-nP transitions have been observed with excellent signal-to-noise ratio, making a frequency stabilization to one of these atomic transitions possible.     

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.     

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.     

Measurement of the fine structure of the n = 4 state of hydrogen

A time-resolved spectroscopy technique has been used to measure the fine structure of the n = 4 state of hydrogen. The excited hydrogen atoms were formed by the use of an electron beam to dissociate molecular hydrogen. The resonance transitions were observed by keeping the radio frequency field fixed and sweeping the magnetic field. Measurements on deuterium were used to study the effects of pressure and motional electric fields. The ²S_1/2 → ²P_1/2 Lamb shift transition , the ²P_3/2 → ²S_1/2 fine structure interval ΔE − L, and the ambient electric field in the measurement volume were determined by using measurements on three separate transitions made at fixed magnetic field. The measurements gave and     

Two-photon time-resolved optogalvanic signals of neon

In this work, temporal evolution of two-photon laser optogalvanic signals of neon has been studied. Optogalvanic signals for four transitions from the metastable 2p⁵3s[3/2]₂ state to 2p⁵4d′[3/2]₁, 2p⁵4d′[3/2]₂, 2p⁵4d′[5/2]₃ and 2p⁵4d′[5/2]₂ states were recorded over a range of discharge currents (3.4–9 mA). It was found that the shape of the optogalvanic signal was strongly dependent on the discharge current so that its peak shifted to shorter times and its amplitude increased with the discharge current. The decay rates of the 4d states, calculated from the optogalvanic signals, were found to increase linearly with the discharge current in the range of 6.2–9 mA. However, for the range of 3.4–5.4 mA, the decay rates were observed to slightly decrease with the discharge current.     

Electric field effects on an optically-pumped HCOOH FIR laser and Zeeman laser theory

Electric field effects have been investigated on the output power of six far-infrared (FIR) laser lines from H¹²COOH optically-pumped by a CO₂ laser with its polarization arranged perpendicular to the Stark field. Optoacoustic signals observed on the pump lines were hardly affected by the applied electric field up to 0.6 kV/cm. By neglecting the electric field effects on the pump transitions, Zeeman laser theory has been applied to the FIR laser transitions. Numerical calculation predicts the observed FIR output power as a function of electric field. Experessions for oscillation frequency and intensity in homogeneous limit are given, which may be applicable to any FIR Stark laser so far as the pump transition is free from electric field effects.     

Two-dimensional optogalvanic spectroscopy

In this work, the time domain of optogalvanic signal is considered as an extra dimension for the analysis of the optogalvanic spectra. A time window was used to integrate over the different time regions of the temporal OG signals for each wavelength. The method enhanced the resolution of spectra considerably so that two closed transitions, which differ only by 4 pm, were precisely separated. In addition a new transition of Neon around 640 nm masked by a transition at 640.229 nm was observed and assigned using the new method.     

System for precise measurement in inverse Raman spectroscopy

A system for precise measurement was developed for inverse Raman spectroscopy, using a cw argon laser and a pulsed dye laser pumped by a YAG laser. The frequency accuracy was assured by monitoring the frequency of both of the lasers with an iodine fluorescence cell or a Fabry-Perot etalon dynamically calibrated by a stabilized HeNe laser. The spectrometer system employed a digitally controlled mechanism to handle the complicated measurement procedure and hence to reduce the overall measurement time. The performance of the system was tested by measuring the CH₄ v₁ lines and the H₂ Q(1) line.