Optogalvanic Spectroscopy Research Articles

Optogalvanic spectroscopy of metastable states in Yb+

The metastable ^{2}F_{7/2} and ^{2}D_{3/2} states of Yb^{+} are of interest for applications in metrology and quantum information and also act as dark states in laser cooling. These metastable states are commonly repumped to the ground state via the 638.6 nm ^{2}F_{7/2} -- ^{1}D[5/2]_{5/2} and 935.2 nm ^{2}D_{3/2} -- ^{3}D[3/2]_{1/2} transitions. We have performed optogalvanic spectroscopy of these transitions in Yb^{+} ions generated in a discharge. We measure the pressure broadening coefficient for the 638.6 nm transition to be 70 \pm 10 MHz mbar^{-1}. We place an upper bound of 375 MHz/nucleon on the 638.6 nm isotope splitting and show that our observations are consistent with theory for the hyperfine splitting. Our measurements of the 935.2 nm transition extend those made by Sugiyama et al, showing well-resolved isotope and hyperfine splitting. We obtain high signal to noise, sufficient for laser stabilisation applications.

Neodymium two-step optogalvanic spectroscopy in a hollow cathode lamp

This paper presents the results of Doppler-limited optogalvanic spectroscopy in commercial neodymium hollow cathode lamp, ranging from 580 to 600 nm. Using the laser multistep excitation technique, five transitions for the first step excitation from the neodymium ground state and seven transitions related to the second step of photoionization scheme were observed. Within these results, for the first time, a new line, 596.645 nm, was observed which could be attributed to a possible two-step transition to neodymium energy level from the 16 979.352 cm − 1 to 33 735.4 cm − 1. The simulated (synthetic) spectra of a mixture of neon (Ne I) and neodymium (Nd I) in this region are compared with experiments in order to facilitate data analysis.

Characterization of hollow cathode fall field strength measured by Doppler-free two-photon optogalvanic spectroscopy via Stark splitting of the 2S level of hydrogen and deuterium

Doppler-free two-photon optogalvanic spectroscopy has been applied to measure the strong electric field strength and the cathode fall characteristics of hollow cathode discharges operated in hydrogen and deuterium via the Stark splitting of the 2S level of atomic hydrogen isotopes. In this paper we show similarities and differences in the tendencies of the cathode fall characteristics of hydrogen and deuterium in a wide range of identical discharge parameters.

Hollow cathode fall field strength measured by Doppler-free two-photon optogalvanic spectroscopy via Stark splitting of the 2S level of hydrogen

It has recently been demonstrated that Doppler-free two-photon optogalvanic spectroscopy is very well suited to measure the strong electric field strength (0.4 kV/cm to 4 kV/cm) present in the cathode fall of hollow cathode discharges, via the Stark splitting of the 2S level of atomic hydrogen and its isotopes. Based on an improved reliability and precision of the measurements, the aim of the present study is to analyze more deeply the dependence of the cathode fall behaviour for a hydrogen discharge on the usual discharge parameters like gas pressure and discharge current; and for changes of the discharge geometry using two different cathode diameters of 10 mm and 15 mm.

14C analysis via intracavity optogalvanic spectroscopy

A new ultra sensitive laser-based analytical technique, intracavity optogalvanic spectroscopy (ICOGS), allowing extremely high sensitivity for detection of 14C-labeled carbon dioxide has recently been demonstrated. Capable of replacing accelerator mass spectrometers (AMS) for many applications, the technique quantifies zeptomoles of 14C in sub micromole CO 2 samples. Based on the specificity of narrow laser resonances coupled with the sensitivity provided by standing waves in an optical cavity, and detection via impedance variations, limits of detection near 10 −15 14C/ 12C ratios have been obtained with theoretical limits much lower. Using a 15 W 14CO 2 laser, a linear calibration with samples from 5 × 10 −15 to >1.5 × 10 −12 in 14C/ 12C ratios, as determined by AMS, was demonstrated. Calibration becomes non-linear over larger concentration ranges due to interactions between CO 2 and buffer gas, laser saturation effects and changes in equilibration time constants. The instrument is small (table top), low maintenance and can be coupled to GC or LC input. The method can also be applied to detection of other trace entities. Possible applications include microdosing studies in drug development, individualized sub-therapeutic tests of drug metabolism, carbon dating and real time monitoring of atmospheric radiocarbon.

Experimental investigations of the hyperfine structure in neutral La: I. Odd parity levels

The results of investigations of the hyperfine structure of electronic levels of the lanthanum atom, performed with laser spectroscopic methods in a hollow cathode discharge (laser-induced fluorescence or optogalvanic spectroscopy), are presented. These concern 35 electronic levels belonging to odd configurations as well as 48 levels belonging to even configurations. In the case of most levels, the hyperfine structure has not been studied before. Moreover, the values of energies and hyperfine structure constants for newly discovered levels of the lanthanum atom are presented: 1 odd level and 22 even levels. On the basis of the hyperfine structure measurements, a consistent spectroscopic description of the levels investigated (including new levels) is proposed. A compilation of all odd electronic levels in the lanthanum atom with experimentally determined hyperfine structure magnetic dipole interaction constants A is presented with the proposed classification and the respective values of the hyperfine structure constants predicted from the semiempirical calculations.

Electric field strengths in a hollow cathode measured by Doppler-free two-photon optogalvanic spectroscopy via Stark splitting of the 2S level of deuterium

We present, in this work, Doppler-free two-photon optogalvanic spectroscopy as a tool to measure the electric field strength in the cathode fall region of a hollow cathode discharge via the Stark splitting of the 2S level of atomic deuterium. The strong electric field strength (1 to 4 kV cm−1) present in the hollow cathode is determined for various discharge conditions (currents from 50 to 200 mA and pressures from 400 to 1350 Pa), which allows investigation of the corresponding variations of the cathode fall and its changes with discharge operation time.

Laser optogalvanic spectroscopy of neon at 659.9 nm in a discharge plasma and nonlinear least-squares fitting of associated waveforms

Laser optogalvanic spectroscopy of neon has been studied in the discharge environment of a hollow cathode discharge lamp. We illustrate the fitting of the time-resolved optogalvanic waveforms by focusing on the 1s 2–2p 2 transition of neon at 659.9 nm and employ a nonlinear least-squares Monte Carlo approach to determine the pertinent amplitude coefficients, decay rates and the instrumental time constant.

One- and two-photon laser optogalvanic spectroscopy of neon in the 570–626 nm region

Eleven two-photon transitions originating from the 2p 53s[3/2] 2, 2p 53s′[1/2] o, 2p 53s[3/2] 1, and 2p 53s′[1/2] 1 states to the 2p 54d configuration states have been investigated in the optogalvanic spectrum of neon in the visible region (570–626 nm) for the first time. The two-photon assignments are confirmed by evaluating the temporal evolution, power dependency, and line widths of the optogalvanic signals. The time evolution of the optogalvanic signals for the two-photon transition originating from the metastable 2p 53s[3/2] 2 state to the 2p 54d′[3/2] 2 state has also been studied at different discharge currents.

High-resolution laser spectroscopy of the hyperfine structure of high-lying levels of Nb i

High-resolution laser spectroscopy techniques have been applied in the wavelength range between 645 and 675 nm to measure the hyperfine structure (hfs) of high-lying levels of atomic niobium. Using Doppler-limited optogalvanic spectroscopy 20 well-resolved spectra were measured and 10 spectra using Doppler-reduced saturation absorption spectroscopy technique. We have precisely determined the magnetic dipole hfs constants A of 42 levels and electric quadrupole hfs constants B of 15 levels. For the first time 17 A constants and 5 B constants were measured.

Intracavity optogalvanic spectroscopy. An analytical technique for 14C analysis with subattomole sensitivity.

We show a new ultrasensitive laser-based analytical technique, intracavity optogalvanic spectroscopy, allowing extremely high sensitivity for detection of (14)C-labeled carbon dioxide. Capable of replacing large accelerator mass spectrometers, the technique quantifies attomoles of (14)C in submicrogram samples. Based on the specificity of narrow laser resonances coupled with the sensitivity provided by standing waves in an optical cavity and detection via impedance variations, limits of detection near 10(-15) (14)C/(12)C ratios are obtained. Using a 15-W (14)CO2 laser, a linear calibration with samples from 10(-15) to >1.5 x 10(-12) in (14)C/(12)C ratios, as determined by accelerator mass spectrometry, is demonstrated. Possible applications include microdosing studies in drug development, individualized subtherapeutic tests of drug metabolism, carbon dating and real time monitoring of atmospheric radiocarbon. The method can also be applied to detection of other trace entities.

Optogalvanic spectroscopy using 389 nm coherent light source accurately tuned to resonance frequency of 23S->33P of 3He

An efficient 389nm coherent light source, made possible through the single-pass second-harmonic generation of a picosecond Ti:sapphire laser with a periodically poled lithium niobate waveguide, was developed for the metastability exchange optical pumping of hyperpolarized 3He gas, which is applicable to imaging with nuclear magnetic resonance. The second-harmonic light provided such a broad spectrum that some split sub-levels of its metastable state under an applied magnetic field could be pumped efficiently and simultaneously. Optogalvanic spectroscopy using the light source indicated that the spectral width of 3He was much less than 70GHz, which was similar to the spectral width of the light source.

Novel Optogalvanic Spectroscopy of Semiconductor Atoms with a Frequency-tripled ns Ti:sapphire Laser Injection-seeded by a cw Frequency-scanning Ti:sapphire Laser

Novel optogalvanic spectroscopy of silicon atoms was conducted with the narrow-linewidth nanosecond pulsed deep-ultraviolet coherent light source which was comprised of the frequency-tripled nanosecond pulsed Ti:sapphire laser injection-seeded by another frequency-scanning cw Ti:sapphire laser. Only when the laser frequency of the seed laser matched with the cavity frequency of the slave laser, signals increased remarkably. The individual spectral widths derived from the injection-seeding effect should be the tolerance for successful injection-seeding in the axial mode of the slave laser, and indicated the linewidth of the injection-seeded ns pulsed deep-ultraviolet laser. So the cavity performances of the slave laser can be seen from the spectrum. The envelope of these peaks indicated the absorption spectrum of silicon atoms. This spectral width had the FWHM of 4.8 GHz in the Gaussian fitting and was equivalent to nearly the pure Doppler width, which could not be measured with the system without the injection seeding.

New even parity autoionisation levels of UI

Even parity autoionisation levels of atomic uranium are investigated in the energy region 51425–51760 cm−1 by two-colour three-photon ionisation spectroscopy in an atomic beam using a time of flight mass spectrometer and in a hollow cathode discharge source using photoionisation optogalvanic spectroscopy. Analysis of the photoionisation spectrum has resulted in identification of 26 new levels and confirmation of 24 levels reported earlier. In addition 9 odd parity levels in the energy region 34525–34860 cm−1 are confirmed.

Spectroscopic measurements of the evanescent wave polarization state

We applied optogalvanic spectroscopy to observe Zeeman effect in the evanescent wave in Ar gas with the help of a single-mode diode laser. The use of an homogenous external magnetic field enabled us to observe different π and σ Zeeman split lines contribution. We studied two orthogonal directions of external magnetic field and two orthogonal polarizations of the incident wave with respect to the plane of incidence. The analysis of relative line strengths leads to the determination of the polarization state of the evanescent wave.

Experimental hyperfine structure investigation of atomic La

Optogalvanic laser spectroscopy has been applied to measure the hyperfine structure of 19 spectral lines of La I in the wavelength regions from 570 to 590 nm and 700 to 825 nm. Experimental hyperfine structure constants A and B of the isotope139La have been measured for 16 levels of odd parity. From those values six magnetic dipole and ten electric quadrupole constants have been determined for the first time. Some disagreements with previously obtained values are discussed.

A study of Stark effects of Rydberg p states of noble gas atoms

We have studied the Stark effect for Rydberg p states of noble gas atoms using laser optogalvanic spectroscopy. The measurements were performed in the sheath region of noble gas glow discharges. Laser excitation from metastable states to np states was monitored by optogalvanic spectroscopy. Clear Stark shifts were observed and the experimental results were compared with a theoretical calculation based on solving the Schrödinger equation of noble gas atoms in an electric field. There was good agreement between the calculation results and the experimental results. The analysis shows that the Stark shift of np states of noble gas atoms can be used for electric field measurements. This method can be a useful alternative to electric field methods based on excitation to nf states because of the higher transition probability of np states.

Espectroscopia optogalvânica: alguns aspectos relevantes

In this work we present the optogalvanic effect in ionized gases in an historical perspective. This effect was observed for the first time by Foote and Mohler in 1925, and explained by Penning in 1928 for mixtures (Ne-Ar) and pure gases (or vapours) in 1937. Also, we show some aspects of the contributions of Romenian authors for the development of optogalvanic spectroscopy, which was used as a new technique only after 1964.

Optogalvanic spectroscopy of the C″Πui5−A′Σg+5 electronic system of N2

We have recorded spectra involving the 3-1, 4-2, 2-0, and 2-2 bands of the C" 5Pi(ui)-A' (5)Sigma+(g) electronic system of N(2) using optogalvanic detection in a discharge through a supersonic jet expansion of argon mixed with a trace of nitrogen gas. The spectra have an effective rotational temperature of about 45 K. They involve all five spin-orbit components of the C" 5Pi(ui) state, which has allowed for precise determination of the spin-orbit coupling in this state. Analysis of the C" 5Pi(ui) state Lambda-doubling shows that it is caused primarily by a first-order spin-spin effect rather than by interaction with Sigma(u) (+/-) states. Our results allow us to assign lines in the 4-2 and 2-0 bands observed in a fluorescence depletion experiment conducted over ten years ago [Ch. Ottinger and A. F. Vilesov, J. Chem. Phys. 103, 9929 (1995)], and to comment on the suggestion that perturbations to the C (3)Pi(u) v=1 level of N(2) arise from interactions with the C" 5Pi(ui) state.

Apparent Isotope Shifts Observed by Two-Step Optogalvanic Spectroscopy

Optogalvanic spectroscopy (OGS) is a method for efficiently detecting atomic and molecular spectra. This technique has been used in frequency locking and stabilization of lasers. So far, various state-selective spectroscopies have been reported. In this note, we suggest that the isotope shifts observed in two-step OGS are affected by the incident direction of exciting lasers, and we estimate the isotope shift of the 1s2–2p4 transition of neon. The schematic energy diagram of a neon atom is shown in Fig. 1. We used a tunable single mode laser diode (LD; Newport, 2010M) with a spectral width of 4MHz, resonant with 1s2–2p4 transition, and a multimode (consisting of 3 to 5 lines) He–Ne laser (Melles Griot, LHP925) with a longitudinal mode spacing of 257MHz, resonant with 2p4–3s2 transition. As shown in Fig. 2, the two laser beams were crossed at an angle of less than 10 and were counterpropagated (case A) and copropagated (case B). A commercial hollow cathode lamp (Hamamatsu Photonics, L2783-3NE-LI) with a Ne pressure of 800 Pa was dc discharged. The discharge voltage and laser power were set to values that prevented self-absorption and self-reversal. The He–Ne laser was chopped at a frequency of f (typically 330Hz), and the two-step excitation signal was detected by a lock-in amplifier. Figure 3 shows the OGS signals obtained without a He–Ne laser (we call it conventional OGS in this note) and detected by scanning the LD frequency through the 1s2–2p4 transition of Ne, along with two-step OGS signals in cases A and B. The conventional OGS signal (1s2–2p4) is relevant to the stationary state of Ne, and the line is Doppler broadened. The isotopic component of Ne appears at the right foot of that of Ne. The resolution in two-step OGS is higher than that in conventional OGS. The central frequency of the 633 nm line (2p4–3s2 transition) of Ne is higher than that of Ne, and this shift is denoted by II. This value is reported to be 0.9GHz by Stahlberg et al. by considering that the He–Ne laser line consists of the lines only from the isotope Ne. In both cases A and B in Fig. 2, the velocity components of Ne atoms are toward the He–Ne laser in order to be Doppler shifted by II and resonant with the 2p4–3s2 transition of Ne atoms. In case A, such Ne atoms are away from the LD and the frequency of the LD should be higher (blue shifted) than the central frequency of the 1s2– 2p4 transition by II. On the other hand, in case B, the two laser beams are in the same direction and the frequency of the LD should be red shifted by II. The higher resolution seen in the two-step excitation is explained by such velocity selection. The apparent isotope shift is determined by deconvoluting the observed curve with two Gaussian peaks, as shown for case B in Fig. 3. The isotope shift for the 1s2–2p4 transition should be the mean value of the two apparent shifts obtained by the two schemes of two-step OGS. The isotope shift thus obtained is estimated at 1:8 0:1GHz. If a He–Ne laser with a single mode is used, the peaks of two-step OGS will become much sharper and a more accurate value of the isotope shift will be obtained.