Showing papers on "Resonance published in 1982"

Laser Deceleration of an Atomic Beam

Abstract: Deceleration and velocity bunching of Na atoms in an atomic beam have been observed. The deceleration, caused by absorption of counterpropagating resonant laser light, amounts to 40% of the initial thermal velocity, corresponding to about 15 000 absorptions. Atoms were kept in resonance with the laser by using a spatially varying magnetic field to provide a changing Zeeman shift to compensate for the changing Doppler shift as the atoms decelerated.

NMR Imaging in Medicine

Abstract: Medical applications of nuclear magnetic resonance (NMR) are discussed. One of the chief advantages of NMR is its ability to generate images of internal body structures without the use of X-rays. In addition to the medical applications. NMR technique is also briefly detailed, along with its advantages over computerized tomography. (JMT)

Observation of Ramsey Fringes Using a Stimulated, Resonance Raman Transition in a Sodium Atomic Beam

Abstract: Ramsey fringes have been observed using a stimulated, resonance Raman transition at 1772 MHz excited by two dye lasers in a sodium atomic beam. The width of the central fringe is 650 Hz (half width at half maximum), corresponding to a 30-cm interaction-region separation. The fringes are free from laser jitter because the jitters in both laser beams are correlated. Applications to frequency standards as well as to high-resolution spectroscopy in the microwave to far-ir regions are discussed.

Direct Frequency Modulation In AlGaAs Semiconductor Lasers

Abstract: Direct frequency modulation characteristics in three different AlGaAs lasers - a channeled-substrate planar (CSP) laser, a buried-heterostructure (BH) laser, and a transverse-junction-stripe (TJS) laser- are studied theoretically and experimentally. Experimental FM responses are measured by using the Fabry-Perot interferometer and birefringent optical filters in the 0-5.2 GHz modulation frequency region. Experimental FM response dependence on modulation frequency, dc bias level, and stripe structure are successfully explained by the theoretical analyses considering both the carrier density modulation effect and the temperature change effect. FM response in the low modulation frequency region from 0 to 10 MHz, gradually decreasing with the modulation frequency, stems from the thermal effect. FM response in the high modulation frequency region from 10 MHz to 5.2 GHz is caused by the carrier effect. A flat FM response of several hundred MHz per 1 mA is observed in the CSP and TJS lasers, but a V-shaped FM response is obtained in the BH laser. Resonance peak due to relaxation oscillation and cutoff characteristics are observed in several gigahertz regions. Weak lateral mode confinement, strong vertical mode confinement, carrier injection outside the effective core region, and p-side down mounts are effective ways to achieve a flat and efficient FM response with a small spurious intensity modulation.

Phosphorus-31 nuclear magnetic resonance of contractile systems

Abstract: Publisher Summary This chapter focuses on techniques and procedures for recording and evaluating the 31 P nuclear magnetic resonance (NMR) spectra of intact muscles and of perchloric acid extracts of muscle At the present time, high-resolution NMR is probably the best general-purpose analytical tool available for studying the chemistry of phosphorus and its compounds With a 31 P NMR probe in a highresolution NMR spectrometer, the analyst can determine easily, and usually within a few minutes, whether phosphorus is present at concentrations greater than 100 μM in fluid samples, characterize each type of phosphorus-containing group present, and obtain a quantitative analysis of the various species present For a spectrometer in which a magnetic field of 23 kiloGauss is employed so that the resonance position of protons is 100 MHz, the 31 P resonance are found at 405 MHz; in a magnetic field 36 times this, the resonance will be found at 1458 MHz

Growth rate calculations of auroral kilometric radiation using the relativistic resonance condition

Abstract: The relativistic cyclotron resonance condition for right-handed extraordinary mode waves defines an ellipse in velocity space. The position of the center and size of the semiminor axis of this ellipse are functions of the plasma frequency, gyrofrequency, wave frequency, and wave normal angle. The effect of varying these parameters on the position and size of the resonance contour is analyzed. The results show that as the wave normal angle decreases, the semiminor axis increases in size and as the plasma frequency to gyrofrequency ratio decreases, the minimum energy for resonating electrons decreases and the maximum wave normal angle allowed by the resonance condition increases. Also, as the wave frequency to gyrofrequency ratio increases, the center of the resonance ellipse moves away from the origin. The relativistic resonance condition and the electron distribution in velocity space obtained by the S3-3 satellite are used to calculate numerically growth rates for the terrestrial auroral kilometric radiation. It is shown that the loss cone region of the electron distribution can give rise to growth rates for the extraordinary mode that are sufficiently large to account for the observed radio emission intensities.

Resonances for the AC-Stark effect

Abstract: The resonance problem for the AC-Stark effect is discussed. We prove that all bound states of the system −(1/2)Δ +V(x) will turn into resonances after an AC-electric field is switched on and the order of the imaginary part of a resonance is determined by the number of the photons it takes to ionize the bound state which is turning into the resonance; if two bound states have energy difference of the photon, there exists a state which oscillates between the two states for a long time.

Resonance, Rate, and Quantum Yield of Infrared-Laser-Induced Desorption by Multiquantum Vibrational Excitation of the Adsorbate C H 3 F on NaCl

Abstract: The linear infrared absorption spectra of C${\mathrm{H}}_{3}$F gas, multilayer film, and C${\mathrm{H}}_{3}$F adsorbate on NaCl crystal surfaces have been found to be distinctly different and significantly coverage dependent. On resonant infrared-laser excitation of the ${\ensuremath{ u}}_{3}$ internal vibration of the adsorbate C${\mathrm{H}}_{3}$F on NaCl, molecular desorption of C${\mathrm{H}}_{3}$F occurs. Measurement of the resonance, rate coefficient, and quantum yield has revealed high spectral selectivity and efficiency of the desorption due to multiphoton ($ng2$) adsorbate vibrational excitation.

Anomalous optical homogeneous linewidths in glasses

Abstract: The homogeneous linewidth is calculated for resonant optical transitions in glasses. The width is due to modulation of the optical levels caused by coupling to the diagonal as well as off-diagonal elements of the two-level modes. The main contribution arises from diagonal modulation of abundant but weakly coupled two-level modes. For a flat density of states of two-level modes and a dipole-quadrupole coupling a large T/sup 1.75/ temperature-dependent behavior is found in good agreement with recent data.

Helium resonance and dispersion effects on geostationary Alfven/ion cyclotron waves

Abstract: To understand observed structure and growth patterns of geostationary Alfven/ion cyclotron waves, the properties of the hot proton cyclotron instability within a helium rich plasma are explored here. This exploration proceeds with an examination of the net linear wave amplifications that result as a wave propagates through the magnetic gradients of a realistic magnetic field model (linearity is discussed and justified). By taking care in generalizing a single pass model to a multiple pass system, the following conclusions have been reached: (1) The basic structure of the frequency gap that is observed close to the helium cyclotron frequency can be explained by the ‘stop-gap’ dispersion effect; however, the helium cyclotron resonance effect contributes to the gap formation leading to He+ ion energization. (2) The presence of the magnetic gradients virtually insures that helium ion energization (by means of the low frequency wave branch only) is the inevitable consequence of the wave generation process. (3) The energized helium ions will sparsely populate a broad range of geomagnetic latitudes (±15 degrees) but will be concentrated strongly within several (2–4) degrees of the geomagnetic equator. (4) The presence of low percentages of helium ions is most likely to suppress the wave generation process (ATS 6 satellite observations support this conclusion for a portion of the wave spectrum).

Method of three-dimensional NMR imaging using selective excitation

Abstract: Selective excitation is used to define a thick planar slab of excited nuclear spins in a nuclear magnetic resonance (NMR) imaging sample. The thick slab is selected such that the excited spins are contained well within the optimum sensitive region defined by the radio frequency (RF) transmitter and receiver coils. Three-dimensional spatial information of an NMR imaging parameter, such as nuclear spin density or nuclear spin relaxation time, is collected simultaneously from the excited slab and can be used to construct a series of several tomographic section images of the slab. The spatial information is encoded in the NMR signal by application of pulsed gradient magnetic fields subsequent to excitation. Image picture information is obtained from the NMR signals via three-dimensional Fourier transformation.

The methyl iodide multiphoton ionization spectrum with intermediate resonance in the A‐band region

Abstract: The 5pπ→6p Rydberg excitations of methyl iodide‐h3 and ‐d3 are observed using multiphoton ionization spectroscopy as two‐photon resonances when excited in the 28 000–32 000 cm−1 region. The two‐photon methyl iodide resonances abruptly cease at 32 000 cm−1, and at higher frequencies are replaced by resonances originating at the 2P1/2 and 2P3/2 levels of the iodine atom. A tentative assignment is also made for a two‐photon resonance in the methyl radical in this region. The replacement of methyl iodide resonances with those of iodine and methyl fragments beginning at 32 000 cm−1 correlates directly with the onset of a one‐photon intermediate resonance in the A band of methyl iodide. When pumping with light of frequency less than 16 000 cm−1, the 5pπ→6p excitations of methyl iodide are observed as four‐photon resonances. However, on entering the A‐band region via two‐photon resonance beyond 32 000 cm−1, no fragment transitions appear. Instead, we observe the three‐photon resonance to the (5pπ, 6s) state of t...

Interaction of adriamycin with DNA as studied by resonance Raman spectroscopy.

Abstract: Raman and resonance Raman spectra of the complex DNA-adriamycin in aqueous solution have been recorded and analysed. Calf thymus DNA was used and it is found that in the complex DNA-adriamycin the chromophore of adriamycin is intercalated in the GC sequences. The substituents on the rings give hydrogen bonding interactions with the base pairs above and below the intercalation site. It is suggested from the Raman and resonance Raman spectral modifications that the phenolic groups of the chromophore are involved in the drug-DNA intercalation, in addition to pi-pi, hydroxyl and amino group interactions.

Phase-modulation laser spectroscopy

Abstract: A novel phase-modulation technique which permits subkilohertz-laser stability and new levels of precision in laser spectroscopy was reported recently. For spectroscopy, the basic arrangement consists of a combination of an optical pump and a probe field which is phase modulated. The pump prepares the atomic sample by burning a narrow hole within the atom's inhomogeneous line shape, and the probe beam samples the prepared hole when its modulation sidebands are swept into resonance. Off resonance, the probe is balanced as pairs of sidebands produce heterodyne beat signals of opposite phase which just cancel. On resonance, the balance is upset and yields a nonvanishing beat signal with a Lorentzian absorption or dispersion line shape and with residual noise approaching the shot noise limit. Here we investigate the theory of phase-modulation spectroscopy. We treat the nonlinear response of an atomic two-level quantum system subject to an intense pump and a weak copropagating or counterpropagating phase-modulated probe beam. The density-matrix equations of motion are solved by a Laplace-transform method and by the novel use of a translation operator which allows the infinite hierarchy of coupled equations to close. A solution equivalent to the rate-equation result is developed and coherence corrections are found which predict new resonances that have just been detected in this laboratory. The delayed pump-probe technique encountered in solid-state laser spectroscopy is analyzed in this context for two- and three-level quantum systems. The response of a Fabry-Perot cavity to a phase-modulated light wave is examined also and reveals an unexpected absorption feature.

Analysis of serum by high-field proton nuclear magnetic resonance.

Abstract: Improvements in nuclear magnetic resonance (NMR) technology are generating an expanding variety of medical applications. In this investigation I have used high-field proton NMR to identify and quantity endogenous and ingested substances in human serum. After addition of a small amount of 2H2O and a reference compound to a 0.4-mL specimen, spectra were recorded for 3 min in Fourier-transform mode, with use of presaturation to suppress the extremely intense H2O peak. Compounds detected at clinically significant concentrations include glucose, alcohols, acetone, organic acids, and salicylate. Less than 1 mmol/L of some of these substances could be detected. For serum containing 20--500 mg of added methanol per liter, peak area was a linear function of concentration (r = 0.998). High-field proton NMR, despite the drawback of expensive, sophisticated instrumentation, offers some unique advantages for clinical chemistry: it permits rapid, specific, nondestructive measurement of several compounds simultaneously, including some that may be inconvenient to measure by conventional means.