Measurements of 220 GHz atmospheric opacity on Mt. Fuji with a radiometer/radome system

We measured atmospheric opacity at 220 GHz at the summit of Mt. Fuji (alt. 3776 m) about one year in order to explore a feasibility of submillimeter-wave astronomical observations. For this purpose, a 220 GHz radiometer system enclosed in a radome (51×51×62 cm³) has been developed. The 220 GHz opacity was lower than 0.06 for a significant fraction ( 45 %) of time from November 1994 to March 1995. Diurnal variation of the opacity at the summit of Mt. Fuji is so small that continuous observation at submillimeter-wave is possible through day and night. Yearly variation of the opacity is studied from water vapor pressure data measured at the weather station for the past 3 years. To prevent accumulation of ice and snow on the Gore-Tex membrane in the radome, the outer membrane was supplied with a thermal flux of 0.63 kW m^–2 and the adjacent metal radome surfaces were supplied with a flux of 0.9 kW m^–2. We evaluate from the 220 GHz transmission data that this heat flux is sufficient to keep the membrane on the radome free of ice and snow during 83 % of the time in 5 winter months. The summit of Mt. Fuji appears to be a promising site for submillimeter-wave observations.     

The observed relationship between the south pole 225-GHz atmospheric opacity and the water vapor column density

We compare our previously reported measurements of South Pole 225 GHz atmospheric opacity,, to the column of precipitable water vapor (PWV) which was derived from concurrent upper air soundings. From this comparison we found that=(2.8±0.1)×10^–2+(6.9±0.2)×10^–2×PWV with in units of nepers/airmass andPWV in units of mm of precipitable H₂O. We compared our results to predictions from Grossman's AT atmospheric transparency model which is widely used in the radio astronomy community. The coefficient of the second term of the above relation, 0.069, was consistent with the predictions from the model; however, the first term, 0.028, which represents the dry air opacity, was about five to ten times larger than expected. Most of this discrepancy between the observed and the predicted dry air opacity can be accounted for by including contributions from continuum emission from N₂ and O₂ as is done in Liebe's MPM atmospheric model.     

A Generalization of the Arzelà–Ascoli Theorem and its Application to Dyson Perturbation Theory

An approximate sequence U_n(t, t₀) for the time-development operator U(t,t₀) has been constructed, when n it approaches the Dyson series. A generalization of the Arzelà–Ascoli theorem for a set of continuous functions to a set of operators is given. We show that if the norm of H(t) in Equation (1.1) is a Lebesgue integrable function with respect to time t, then the Dyson series is uniformly weak convegent and Equation (1.1) has a unique solution. The preliminary application of the above results to quantum mechanics is studied.     

Ramanujan’s ‘‘Lost Notebook’’ and the Virasoro Algebra

By using the theory of vertex operator algebras, we gave a new proof of the famous Ramanujans modulus 5 modular equation from his Lost Notebook (p. 139 in [R]). Furthermore, we obtained an infinite list of q-identities for all odd moduli; thus, we generalized the result of Ramanujan.Acknowledgements It was indeed hard to trace all the known proofs of (1.1), (1.2) and (1.3). We apologize if some important references are omitted. We would like to thank Jim Lepowsky for conversations on many related subjects. A few years ago Lepowsky and the author were trying to relate classical Rogers-Ramanujan identities and Zhus work [Z]. We also thank Bruce Berndt for pointing us to [BrO] and Steve Milne for bringing [Mi] to our attention.     

Ignition thresholds for deuterium-tritium mixtures contaminated by high-<Emphasis Type="Italic">Z</Emphasis> material in cone-focused fast ignition

Evaluations of the energy for thermonuclear ignition of a compressed deuterium-tritium mixture contaminated by a high-Z material are presented. Mixing at the atomic level is considered and the results are given as a function of the contaminant fraction. The reference situation is that of cone-focused fast ignition (CFFI). The numerical 2D simulations for this study were performed by a Lagrangian 2D hydrocode that includes real matter EoS, real matter opacity coefficients, and packages for finite-range energy deposition by reaction products and the relative in-flight reactions. A simple estimate is presented for the effects of high-Z material blobs on the ignition energy (macroscopic mixing). Possible sources for fuel contamination in CFFI are discussed.     

Generation of broadband squeezed states pumped by CW mode-locked pulses

Broadband high level squeezing was clearly observed from 100 kHz to 80 MHz using crystals Ba₂NaNb₅O₁₅ of 5 mm length, MgO:LiNbO₃ of 19 mm length and KNbO₃ of 5.8 mm length. Maximum noise reductions detected on a spectrum analyzer were –1.2 dB (–24%), –1.25 dB (–25%), and –1.8 dB (–34%) for the three crystals, respectively. The maximum squeezing is limited mostly by optical index damage of the parametric crystals. A detailed analysis of the beam parameters traced along the pump beam, squeezed vacuum, etc. is given. A detailed discussion on the evaluation of the initial squeezed level is given. A preliminary experiment with compressed laser pulses to avoid the optical damage is also described.     

Observation of gain at 54.2 Å on balmer-alpha transition of hydrogenic sodium

Planer stripe and foil targets coated with NaF were irradiated with high intensity 351 nm laser radiation of 130 ps duration. Time-integrated as well as time-resolved measurement of gain on NaXIH at 54.2Å were made. A time-integrated gain of 1.2 _–1.1 ^+0.8 cm^–1 and a time-resolved peak gain of 3.2±1.0 cm^–1 were obtained. A detailed account of the experimental procedures for determination of gain is given.     

Measurement of atmospheric opacity at 278 GHz at McMurdo Station, Antarctica in austral spring seasons, 1986 and 1987

We present a quasi-continuous record of measured atmospheric opacity obtained at 278 GHz (1.1 mm wavelength) from McMurdo Station, Antarctica during austral spring seasons in 1986 and 1987. McMurdo Station, at 78°S, 166°W, is easier to access than the Amundsen-Scott (South Pole) Station, although representing a warmer, sea level site with substantially higher typical opacity: the present record may be of interest to those contemplating mm-wave astronomical or atmospheric observations within the Antarctic region. Observations were made over a 256 MHz bandpass in 1986, during the period August 30 to October 30. In 1987, a 512 MHz bandpass was used, and observations were made during the period September 4 to October 13. All data are reduced to represent opacity in the zenith direction, and measurements were taken approximately every 20 minutes, except during storms or other periods of high opacity. The periods covered represent transitions from the polar winter towards summer conditions, and thus represent neither the best nor the worst that this site has to offer.     

Plasma effects in picosecond-femtosecond UV laser ablation of polymers

Laser ablation of polyimide (PI) and polymethyl-methacrylate (PMMA) at 248 nm with pulse lengths ranging from 200 fs to 200 ps was investigated. The measured ablation rates show minima for pulse lengths of about 5 ps (PMMA) or 50 ps (PI).The reflected fraction of the ablating laser pulse was measured as a function of the pulse length. In the case of PMMA maximum reflectance corresponds to a minimum ablation rate.This behavior can be explained by a dynamic plasma reflection model: A fast build up of a dense plasma is followed by high obscuration for a brief transition time and a self-regulating opacity for the rest of the pulse. This model of plasma mediated ablation leads to a ^1/4-dependence of the ablation rate at fixed fluence, which fits very well to the measured data, in particular if an extension to nanosecond ablation data of PI and PMMA is considered. PACS 52.50.Jm; 61.80.Ba; 42.65.Re     

Behavior of bubbles induced by the interaction of a laser pulse with a metal plate in water

When a pulsed laser beam is focused onto a metal plate in water, a high-pressure pulse can be generated. This paper investigates the formation and behavior of bubbles that appear after the high-pressure-pulse generation. A 200-mJ, second-harmonic Nd:YAG laser pulse (duration of 7 ns) is incident on a stainless steel (SUS 304) plate to form a 1.1-mm-diameter spot. A bubble is formed and expands over the spot, which generates a hemispherical blast wave around the spot. The bubble grows in a period of the order of 400 s after the laser pulse to reach a radius of about 5 mm. The behavior of the bubble is strongly affected by the thickness of the plate. When the plate thickness is 10 mm, the bubble keeps its hemispherical shape during the period of the first bounce. However, with a thin plate, for example of 0.1-mm thickness, the bubble is pinched and its head separates; moreover, another bubble is generated on the other side of the plate. Since these bubbles have different bounce motions, the acoustic field between 400 and 900 s significantly differs depending on the thickness of the plate. PACS 47.40.Nm; 68.45.-v; 42.62.Cf