Charles M. Klimcak

Laser spectroscopy on a ‘‘shoestring’’

The advent of tunable lasers has had a profound influence on both experimental and theoretical physics. Unfortunately, since these laser systems are typically hazardous and expensive, the physics student at the undergraduate or first‐year graduate level has no real familiarity with their application in modern physics; and thus cannot fully appreciate their significance. Tunable single mode laser diodes, however, may offer a remedy to this situation. To demonstrate their applicability, we have designed a relatively simple and inexpensive experiment of laser diode spectroscopy in an atomic beam which illustrates the effect of hyperfine structure and the isotope shift in the rubidium D1 transition (52S1/2−52P1/2). Furthermore, this experiment demonstrates the possibility of investigating basic physics without major expenditures for laser systems and laboratory facilities.

Generation of ion-acoustic waves in an inductively coupled, low-pressure discharge lamp

For a number of years it has been known that the alkali rf-discharge lamps used in atomic clocks can exhibit large amplitude intensity oscillations. These oscillations arise from ion-acoustic plasma waves and have typically been associated with erratic clock behavior. Though large amplitude ion-acoustic plasma waves are clearly deleterious for atomic clock operation, it does not follow that small amplitude oscillations have no utility. Here, we demonstrate two easily implemented methods for generating small amplitude ion-acoustic plasma waves in alkali rf-discharge lamps. Furthermore, we demonstrate that the frequency of these waves is proportional to the square root of the rf power driving the lamp and therefore that their examination can provide an easily accessible parameter for monitoring and controlling the lamp’s plasma conditions. This has important consequences for precise timekeeping, since the atomic ground-state hyperfine transition, which is the heart of the atomic clock signal, can be signifi...

Photothermal wavelength modulation of a diode laser

We describe a photothermal technique for wavelength modulation of a room-temperature diode laser at modulation frequencies up to a few kilohertz. This photothermal modulation is accomplished by exposing the diode laser to a low-power, amplitude-modulated helium–neon-laser beam. Advantages of photothermal wavelength modulation compared with the typical injection-current wavelength modulation are discussed.

Ultrasensitive detection of aromatic hydrocarbons by two‐photon photoionization

An optimized multiphoton photoionization detection system has been applied to monitor aromatic‐hydrocarbon vapor density as a function of temperature. The density curves established for naphthalene by this procedure permit estimation of a detection limit of 5×104 molecules/cm3 in a nitrogen buffer gas. With slight modification this method woud be capable of single‐molecule detection limits.

Production of mass-selected neutral clusters of rubidium

Abstract Charge neutralization of rubidium cluster ions (Rb N + ) by Rb atomic vapor is reported. The cluster ions are generated by a liquid metal ion source (LMIS). The ions and the neutrals are detected directly without any photoionization step. The extent of dissociative neutralization is negligible. This results in intense, mass-selected neutral cluster beams. The charge exchange cross sections for Rb 2 + and Rb 3 + with Rb, are 9.3× 10 −15 and 3.1 × 10 −15 cm 2 respectively.

Liquid metal ion source for cluster ions of metals and alloys : design and characteristics

Currently liquid metal ion sources (LMISs) are of great interest for a wide variety of applications—ion implantation, ion microlithography, thrusters for electric space propulsion, etc. A novel application of the LMIS is for the production of metallic cluster ions. In our laboratory we have designed and optimized the performance of a LMIS for the production of cluster ions of alkali metals. Using liquid rubidium (Rb) we have observed copious production of singly charged cluster ions (Rb+N, N=1–100). As expected the largest fraction of the emission consists of atomic ions. For low source current ( 80 μA) we observe cluster ions as large as Rb+100. We study the mass distribution using the time‐of‐flight technique.

Ultrasensitive Molecular Detection By Multiphoton Ionization Spectroscopy

In this paper we describe molecular detection methods based on Multi-Photon Ionization (MPI) spectroscopy that provide high selectivity in addition to excellent detection limits. Prior work based on one-wavelength resonance enhanced 2-photon ionization spectroscopy is reviewed. Highlights include improvement of detection limits for aromatic hydrocarbons by a factor of one-thousand and adaptation of 2-photon ionization for spectrally selective detection in gas chromatography. Two alternative approaches for highly selective MPI detec-tion are discussed. Time-of-Flight (TOF) ion analysis in conjunction with MPI provides mass spectral signatures in addition to MPI spectra. Single ion sensitivity can be approached in this configuration. In a purely optical approach, selectivity can be improved by using two-color excitation. The new two-color method of Ion Dip Spectroscopy (IDS) can be used to label specific intermediate states involved in the MPI process and it is capable of generating Raman-type spectra as a supplement to the MPI spectra. The ultimate detection limit of the IDS method is expected to be about 104 molecules/ cm3, which is comparable to the detection limit that we have obtained for naphthalene by one-color MPI.

Alkali metal consumption by discharge lamps fabricated from GE-180 aluminosilicate glass

Alkali rf-discharge lamps provide the light for optical pumping in vapor-cell atomic clocks and magnetometers. Traditionally, the discharge lamps envelope has been fabricated from alkali-resistant Corning 1720 aluminosilicate glass, and such lamps have demonstrated decade-long continuous operation. Specifically, the diffusion of alkali atoms into this glass during lamp operation has been shown to be sufficiently slow that lifetimes in excess of ten years can be obtained using only moderate initial alkali fill levels (<; 400 μg). However, Corning 1720 glass is no longer being manufactured. It is therefore important to identify alternative glass types that offer comparable alkali resistance, and that are readily available. Although Schott 8436 aluminosilicate glass has been shown to be a suitable substitute, it would be advantageous to identify an alternate glass type produced in higher volume. One alternative, which is manufactured in very high volume for use in automotive lamps, is GE-180 glass. Although this glass also offers high alkali resistivity due to its aluminosilicate composition, the rate of diffusion of alkali atoms into this material when employed as the glass envelope of an rf-discharge lamp has not been measured. We present here our initial results, obtained by Differential Scanning Calorimetry (DSC), of the rate of Rb consumption by discharge lamps manufactured with GE-180 glass. Our results suggest that GE-180 is an excellent substitute for Corning 1720 glass in rf-discharge lamps. We also discuss some unusual issues that have been observed during our DSC measurements, and we outline some new methods for attaining accurate alkali lamp fills using the DSC technique.

Development of a fiber optic chemical dosimeter network for use in the remote detection of hydrazine propellant vapor leaks at Cape Canaveral Air Force Station

Fiber optic chemical dosimeters are being developed for use in the remote detection of toxic rocket propellant vapors, (hydrazine and its derivatives, and nitrogen tetroxide) that are used at Air Force and civilian rocket launch sites. The dosimeters employ colorimetric indicators that react selectively and irreversibly with the propellant vapors to yield chemical compounds that absorb laser light launched into a fiber optic network. The dosimeters are fabricated by dispersing the reagent within either a porous cladding or a porous distal end coating, that is prepared by a low temperature sol-gel technique. Remote field- scale detection of hydrazine vapor in a few hundreds of ppb-min integrated dose regime has been demonstrated with a network that is approximately equals 1 kilometer in length and the use of a low power (10 mW) diode laser. We have also assembled a computer model of a multimode fiber optic dosimeter network for prediction of the operational capabilities of a multiplexed system containing 100 dosimeters. The model was encoded in both spreadsheet and BASIC formats. It was used to evaluate the performance of a field-scale, remote fiber optic detection system incorporating discrete chemical vapor dosimeters in serial, parallel, or hybrid serial/parallel topologies. Additionally, we have begun exploratory work utilizing chemical reagents that react reversibly with hydrazine vapor to develop hydrazine vapor concentration sensors that could be deployed in a similar fashion on a remote fiber optic network to detect hydrazine vapor in the ppb regime.

Harmonic saturated spectroscopy applied to molecular photoacoustic detection

The feasibility of the application of harmonic saturated spectroscopy to molecular detection in the infrared regime was investigated. Experimental measurements using SF6 as a model gas were performed with a CO2 laser photoacoustic molecular vapor detector operating in the 9–11-μm portion of the infrared regime. These experiments demonstrated the negligible loss of absolute sensitivity, the maintenance of a characteristic readily identifiable absorption profile, and the ability to scale with laser intensity in the proper conditions. Our work demonstrates the importance of a laser modulation waveform that is completely devoid of spatial asymmetries for the realization of the full potential of this method.