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We present a study of the first silicon microdisk resonators which are smaller than the free-space resonant wavelength in all spatial dimensions. Spectral details of whispering gallery modes with azimuthal mode number m = 4-7 are measured in microdisks with diameters between 1.35 and 1.89microm and are studied at wavelengths from 1.52 to 1.62microm. For the structures considered here, m = 5 is the highest azimuthal mode order in a subwavelength cavity and has measured Q = 1250. These results agree well with theoretical calculations using a finite difference frequency domain method and fit an exponential scaling law relating Q to disk radius via m.

Data on continuum electron capture and loss for bare and highly ionized C a+ ,O a+ ions traversing Ar at energies 1.6-2 C 8 MeV/A reveal striking disagreements with corresponding theories. We demonstrate a velocity-independent (~z 2 ' 2±0t2 ) scaling for continuum capture by bare ions, a Z -independent velocity scaling, and an approximately ^-independent (q = 6,7,8) equality of continuum electron-capture and -loss cross sections at velocities corresponding to ~ 2 MeV/A 0

The lifefimes of the (2p)2 P 3/2 level in Si XII and the (2p 2)3 P 2,1,0, (2s2p)1 P 1 and the (2p 2)1 D 2 levels in Si XI have been determined using the beam-foil method. It is proposed that existing discrepancies between experimental and theoretical f values for the (2s 2)1 S 0-(2s2p)1 P 1 transition in some ions of the Be sequence may be the result of the inability of the experimentalist to account for strong cascading from the (2p 2)1 S 0 level.

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The first measurements of the mean energies E"ofhighly charged recoil ions detected in coincidence with multiply ionized swift projectiles are reported. Beams of 23-, 27.6-, and 33-MeV Cl'+ produced Ar recoil ions whose mean energies exhibited a strong dependence on the product (qr) of final projectile and recoil charge states. For large qr values, F" is substantially larger than earlier estimates, and allows inference of characteristic impact parameters without requiring measurements of projectile scattering angle.In the past decade, the production of low-energy highcharge-state recoil ions by swift, heavy-ion impact has been effectively exploited. Low-emittance recoil-ion sources have been used to provide spectroscopic sources of low Doppler spread, as well as to produce secondary beams for slow ion-atom collision experiments. ' The "ion-hammer" technique has proven a rich source of novel data on ion-atom collision phenomena, particularly on single-and multiple-electron capture in the 0.1-to-few keV per charge energy range. ' The possibility of producing a powerful, parasitic source of bare and few-electron lowenergy ions (greater than 10' extracted ions/sec), "hammered" at MHz frequencies in a heavy-ion storage ring, has been conjectured by Ullrich et al. Despite the abundance of activity in the field and the importance of the parasitic-ion-source possibility, few data concerning the energies and angular distributions of the primary recoil ions have been published.Ullrich et al.have recently published a measurement of the entire recoil-energy distribution for Ne + ions produced by 1.4-Mev/u U projectiles, using a specially designed time-offlight (TOF) spectrometer. Substantial new knowledge of intrinsic interest, as well as practical significance for design of parasitic sources, can be gained from measurements of recoil energies and angular distributions. This paper concerns the first quantitative measurements of the mean energies E, of slow, highly charged recoil ions produced in MeV/u collisions as a function of recoil-ion charge state r and emergent projectile charge state q. For high (q, r) values, E" is found to be several times larger than suggested by earlier estimates (made for more restrictive assumptions than apply here. ' The steep dependence of E"on q and r observed permits inference of a characteristic impact parameter b corresponding to the mean recoil energy for each (q, r) pair.This method thus augments difficult measurements of projectile scattering angle in coincidence with one or more reaction fragments, a method primarily useful for harder collisions and often requiring angular resolution of -100 prad. Since calculated target ionization transition probabilities are not sharply peaked in b, but typically extend over a range comparable to b, one expects the recoil ions to be spread over a corresponding range in E"and recoil angle. Present measurements are of mean recoil energies and thus indicate b, but not its range.The measurements were performed using a TOF method' already demonstrated (i...

Studies have been made of uv and metastable excitation functions for H2 near threshold.Within 2 eV of threshold the total cross sections appear to be dominated by two vibrational series of resonances. In the excitation function of B~Z+"(uv emitting), one series (band "a") is ten times more intense than the other (band "c"), while for c II"excitation (metastable), the two series have approximately equal intensity. The measured energy positions of the resonant peaks agree-well with results obtained by other experimental techniques and with theory. Energy calibration of the metastable excitation function has confirmed that the c II" (v =0) level is metastable, and there was no obvious threshold for a second metastable vibrational level, although the nature of the data does not preclude its existence.