We have produced a rf discharge in 40Ar and used saturated absorption spectroscopy to offset lock a Ti:Sapphire laser to the absorption peak of the 43P243D3 cooling transition at 811 nm. We describe the procedure for fabrication of the cell and production of the discharge

Busch, H. C.

Sukenik, C. I.

English

Old Dominion University

Old Dominion UniversityODU Digital CommonsPhysics Faculty Publications Physics2-2002A Rf Discharge Cell for Saturated AbsorptionSpectroscopy of Metastable ArgonC. I. SukenikOld Dominion University, csukenik@odu.eduH. C. BuschOld Dominion UniversityFollow this and additional works at: https://digitalcommons.odu.edu/physics_fac_pubsPart of the Atomic, Molecular and Optical Physics CommonsThis Article is brought to you for free and open access by the Physics at ODU Digital Commons. It has been accepted for inclusion in Physics FacultyPublications by an authorized administrator of ODU Digital Commons. For more information, please contact digitalcommons@odu.edu.Repository CitationSukenik, C. I. and Busch, H. C., "A Rf Discharge Cell for Saturated Absorption Spectroscopy of Metastable Argon" (2002). PhysicsFaculty Publications. 13.https://digitalcommons.odu.edu/physics_fac_pubs/13Original Publication CitationSukenik, C.I., & Busch, H.C. (2002). A Rf discharge cell for saturated absorption spectroscopy of metastable argon. Review of ScientificInstruments, 73(2), 493-494. doi: 10.1063/1.1433953A rf discharge cell for saturated absorption spectroscopy of metastable argonC. I. Sukenik and H. C. Busch  Citation: Review of Scientific Instruments 73, 493 (2002); doi: 10.1063/1.1433953 View online: http://dx.doi.org/10.1063/1.1433953 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/73/2?ver=pdfcov Published by the AIP Publishing  Articles you may be interested in An oscillator circuit to produce a radio-frequency discharge and application to metastable helium saturatedabsorption spectroscopy Rev. Sci. Instrum. 83, 044705 (2012); 10.1063/1.4705999  Absorption spectroscopy measurements of argon metastable and resonant atom density in atmospheric pressureAr-He surface-wave plasmas using a low pressure lamp J. Appl. Phys. 111, 023303 (2012); 10.1063/1.3671408  The role of carrier gases in the production of metastable argon atoms in a rf discharge Rev. Sci. Instrum. 80, 036105 (2009); 10.1063/1.3105722  Hydrogenated-amorphous carbon nitride films formed from the dissociative excitation reaction of CH 3 CN withthe microwave-discharge flow of Ar: Correlation of the [N]/([N]+[C]) ratio with the relative number densities of theCH (A 2 Δ) and CN (B 2 Σ + ) states J. Vac. Sci. Technol. A 22, 487 (2004); 10.1116/1.1690250  Study of an RF discharge with mercury and argon: Effect of argon metastable quenching by mercury reactions AIP Conf. Proc. 563, 29 (2001); 10.1063/1.1374881    Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP:  128.82.253.131 On: Wed, 24 Aug2016 15:17:54A rf discharge cell for saturated absorption spectroscopyof metastable argonC. I. Sukenika) and H. C. BuschDepartment of Physics, Old Dominion University, Norfolk, Virginia 23529~Received 9 October 2001; accepted for publication 15 November 2001!We have produced a rf discharge in40Ar and used saturated absorption spectroscopy to offset locka Ti:Sapphire laser to the absorption peak of the 43P2→43D3 cooling transition at 811 nm. Wedescribe the procedure for fabrication of the cell and production of the discharge. ©2002American Institute of Physics.@DOI: 10.1063/1.1433953#Noble gases, alkali, and alkaline earth atoms are theprincipal species studied in experiments in laser cooling andtrapping of atoms.1 Unlike the alkalis and alkaline earths,though, noble gases must be trapped in an excited metastablestate because laser sources in the vacuum ultraviolet for ini-tiating a cooling transition from the ground state are notreadily available. Excitations from metastable states, by con-trast, are conveniently located in the visible to near infraredspectral region. For example, the 43P2→43D3 cooling tran-sition in 40Ar occurs at 811 nm. We are planning to carry outstudies of ultracold molecule production in a dual speciesmagneto-optic trap containing both rubidium and argon. As aresult, we have constructed an rf discharge cell and used it tolock a Ti:Sapphire laser for trapping argon atoms. The use ofboth rf discharge and direct current discharge cells has beenreported in the literature, but details on the construction ofthe cell are often omitted. Furthermore, problems with deg-radation of the cell over time, presumably due to contamina-tion, have also been noted. Luet al. recently described theconstruction of a direct current discharge for saturated ab-sorption spectroscopy in helium.2 In this Note, we detail howwe fabricated and operate a rf discharge cell for saturatedabsorption spectroscopy in argon.We chose to use a rf discharge cell as opposed to a directcurrent discharge cell so as to eliminate the possibility of cellcontamination resulting from sputtering of the electrodes, acommon problem. The cell was made entirely from Pyrexglass. It is circular in cross section with a 1 in. diameter, andis 3 in. long. Although the optical quality of the Pyrex blankswhich were glass blown onto the ends of the cell is not asgood as optical flats, it is easier to fabricate than fritting a flatand works fine for saturated absorption spectroscopy. A smallPyrex tube stem was blown onto the center of the cell forevacuation and loading of the argon. The other end of thestem was blown onto a commercial glass-to-metal connectorterminated with a 1 1/3 in. miniconflat flange as shown inFig. 1.To reduce the possibility of contamination of the dis-charge over time, considerable care was taken to thoroughlyclean the glass cell. The first step of the cleaning processinvolves chemical cleaning. The cell was placed in a heatedultrasonic bath with Alconox detergent for about 1 h. Thecell was then thoroughly rinsed using deionized water fol-lowed by methanol. Finally, the inside of the cell was ex-posed to a 50% solution of hydroflouric acid for approxi-mately 1 min followed by a second methanol rinse. At thispoint, the cell was ready to be placed on the vacuum mani-fold used for evacuation and filling. We used a small conflatvacuum system attached to a 60 l/s Varian ion pump. A lec-ture bottle containing research grade argon was also attachedto the vacuum system at this time. The entire vacuum systemwas roughed out and the ion pump started. The regulator onthe lecture bottle was left open to purge the incoming gaslines directly to the lecture bottle valve. Once the vacuumsystem had reached a pressure of about 131027 Torr, asmeasured by the current on the ion pump, the cell wasflamed with a Bunsen burner for about 15 min, sufficient todrive most of the remaining contaminants off the interior ofthe cell walls.As a final cleaning measure, the cell was filled with sev-eral Torr of research grade argon, valved off, and a rf dis-charge~described next! operating at 3 W, was allowed to runfor 1 h. The electron bombardment helps to remove any re-maining contaminants embedded near the surface. After thea!Electronic mail: csukenik@odu.edu FIG. 1. Sketch of the Pyrex cell used to make a rf discharge in argon.REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 73, NUMBER 2 FEBRUARY 20024930034-6748/2002/73(2)/493/2/$19.00 © 2002 American Institute of Physics Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP:  128.82.253.131 On: Wed, 24 Aug2016 15:17:54discharge cleaning procedure, the cell was once again evacu-ated and allowed to pump overnight. Finally, the cell wasfilled with approximately 50 mTorr of argon and a torch wasused to pinch off the stem, leaving a sealed cell. The ultimatepressure of the cell before filling with argon was,131027 Torr.The rf discharge was produced by wrapping a coil,which serves as an antenna, around the cell. We found thedimensions of the coil are not critical. The coil, which wasmade using 14 gauge magnet wire, consisted of 20 turnswrapped just outside the glass cell with the wires terminatedto a BNC connector. The discharge was driven by a voltagecontrolled oscillator~Mini-Circuits ZOS-50!/amplifier ~ENI300P! combination. The amplifier was able to deliver up to 4W of power, but we found that the discharge can be sustainedeasily with as little as 400 mW. We typically drove the dis-charge at 25 MHz, though it worked fine over a range offrequencies. In order to ensure that the forward power isdelivered to the cell and not simply reflected by the coil,impedance matching is critical. Impedance matching can beachieved with a simple roller inductor as shown in Fig. 2. Wefound it convenient to purchase a commercial antenna tuner~MFJ 969! which is manufactured primarily for amateur ra-dio enthusiasts. To achieve the best possible impedancematching, a roller inductor—which allows for continuoustuning—is preferable to a step inductor which only allowsfor discrete tuning. The MFJ 969 also has a built-in forwardand reverse power meter for monitoring the power deliveredand the standing wave ratio. Using the antenna tuner, wewere able to impedance match such that the reflected powerwas less than 5% of the incident power.With rf sources, interference in other electronics frombroadcasting can be a problem. We found that although thecell itself did not seem to cause much interference, thesimple coaxial cable~RG-58! that we used to deliver the rfdid create substantial interference in nearby electronics. Thisinterference was virtually eliminated, though, by wrappingthe entire length of the coax cable with a grounded cylindri-cal mesh.We have fabricated a rf discharge cell for saturated ab-sorption spectroscopy in40Ar. Fabrication of the cell re-quires attention to proper cleaning in order to avoid degra-dation of the cell over time. Proper impedance matching ofthe rf source to the coil is also important. A simple rollerinductor does the job nicely. In order to reduce rf broadcast-ing throughout the lab, the coaxial cable used to deliver therf from the source to the coil should be shielded. We haverun the cell in a standard saturated absorption spectrometer3several days a week for three months with no indication ofline broadening or quenching arising from cell contamina-tion. These observations lead us to expect that the cell willoperate for years.The authors thank M. D. Havey for useful discussionsand assistance with the glassblowing. They also thank S.Popovic, M. S. Walhout, and C. R. Orzel for useful discus-sions.1H. J. Metcalf and P. van der Straten,Laser Cooling and Trapping~Springer, New York, 1999!.2W. Lu, D. Milic, M. D. Hoogerland, M. Jacka, K. G. H. Baldwin, and S.J. Buckman, Rev. Sci. Instrum.67, 3003~1996!.3W. Demtroder,Laser Spectroscopy~Springer, New York, 1996!.FIG. 2. Schematic of a simple circuit which uses a roller inductor to im-pedance match the rf source to the cell coil.494 Rev. Sci. Instrum., Vol. 73, No. 2, February 2002 C. I. Sukenik and H. C. Busch Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP:  128.82.253.131 On: Wed, 24 Aug2016 15:17:54

A Rf Discharge Cell for Saturated Absorption Spectroscopy of Metastable Argon

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A Rf Discharge Cell for Saturated Absorption Spectroscopy of Metastable Argon

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