scholarly journals Two-color modulation transfer spectroscopy

2009 ◽  
Vol 87 (1) ◽  
pp. 95-100 ◽  
Author(s):  
A Pérez Galván ◽  
D Sheng ◽  
L A Orozco ◽  
Y Zhao
Keyword(s):  
Velocity Distribution ◽  
Excited States ◽  
Signal To Noise Ratio ◽  
Modulation Transfer ◽  
Signal To Noise ◽  
Atomic Properties ◽  
Laser Frequencies ◽  
Step Transition ◽  
Good Signal

We present two-color modulation transfer spectroscopy as a tool for precision studies of atomic properties of excited states. The bi-colored technique addresses a narrow set of velocity groups of a thermal atomic vapour using a two-step transition to “burn a hole” in the velocity distribution. The resulting spectrum presents sub-Doppler linewidths, good signal-to-noise ratio and the trademark sidebands that work as an {in situ} ruler for the energy spacing between atomic resonances. The spectra obtained can be used for different applications such as measurements of energy splittings or stabilization of laser frequencies to excited atomic transitions.PACS Nos.: 32.10.Fn, 32.30.–r, 42.50.Gy, 42.60.Fc

Determination of the Best Emulsion for the Microscopy of Crystals

1981 ◽  
Vol 39 ◽  
pp. 32-33
Author(s):  
David A. Grano ◽  
Kenneth H. Downing
Keyword(s):  
Spatial Frequency ◽  
Information Transfer ◽  
Signal To Noise Ratio ◽  
Experimental Situation ◽  
Photographic Emulsion ◽  
Modulation Transfer ◽  
Signal To Noise ◽  
Frequency Space ◽  
Noise Ratio

The retrieval of high-resolution information from images of biological crystals depends, in part, on the use of the correct photographic emulsion. We have been investigating the information transfer properties of twelve emulsions with a view toward 1) characterizing the emulsions by a few, measurable quantities, and 2) identifying the “best” emulsion of those we have studied for use in any given experimental situation. Because our interests lie in the examination of crystalline specimens, we've chosen to evaluate an emulsion's signal-to-noise ratio (SNR) as a function of spatial frequency and use this as our critereon for determining the best emulsion.The signal-to-noise ratio in frequency space depends on several factors. First, the signal depends on the speed of the emulsion and its modulation transfer function (MTF). By procedures outlined in, MTF's have been found for all the emulsions tested and can be fit by an analytic expression 1/(1+(S/S0)2). Figure 1 shows the experimental data and fitted curve for an emulsion with a better than average MTF. A single parameter, the spatial frequency at which the transfer falls to 50% (S0), characterizes this curve.

Estimating Optimum Filter Length in Linear Prediction

1997 ◽  
Vol 51 (5) ◽  
pp. 718-720 ◽  
Author(s):  
O.-P. Sievänen
Keyword(s):  
Raman Spectra ◽  
Prediction Error ◽  
Linear Prediction ◽  
Signal To Noise Ratio ◽  
New Method ◽  
Signal To Noise ◽  
Filter Length ◽  
Optimum Filter ◽  
Good Signal ◽  
Prediction Filter

In this article a new method to estimate optimum filter length in linear prediction is described. Linear prediction was used to enhance resolution of a spectrum. In particular, the dependence of prediction error on filter length has been studied. With calculations of simulated spectra it is shown that the prediction error falls rapidly when the filter length attains its optimum value. This effect is quite pronounced when the spectrum has a good signal-to-noise ratio and the modified covariance method is used to calculate prediction filter coefficients. The method is illustrated with applications to real Raman spectra.

Metastable yield of argon between 23 and 37 eV by electron impact

1979 ◽  
Vol 57 (10) ◽  
pp. 1624-1633 ◽  
Author(s):  
P. Marchand ◽  
J. Cardinal
Keyword(s):  
Electron Impact ◽  
Excited States ◽  
Signal To Noise Ratio ◽  
Negative Ion ◽  
Photon Yield ◽  
Large Signal ◽  
Signal To Noise ◽  
Monoenergetic Electron ◽  
Yield Curves ◽  
Noise Ratio

The metastable yield of argon excited by monoenergetic electron impact has been measured between 23 and 37 eV. Thanks to a large signal-to-noise ratio, many very small structures have been detected superimposed on the metastable continuum and are attributed to Ar− negative-ion states and to highly excited states of Ar. The results are compared with broadband photon yield curves and electroionization curves.

Ten-Nanosecond Step-Scan FT-IR Absorption Difference Time-Resolved Spectroscopy: Applications to Excited States of Transition Metal Complexes

1997 ◽  
Vol 51 (4) ◽  
pp. 580-583 ◽  
Author(s):  
Pingyun Chen ◽  
Richard A. Palmer
Keyword(s):  
Excited State ◽  
Excited States ◽  
Signal To Noise Ratio ◽  
Ir Absorption ◽  
Decay Kinetics ◽  
Time Resolved ◽  
Ligand Charge Transfer ◽  
Ft Ir ◽  
Good Signal ◽  
Nanosecond Time Resolution

Ten-nanosecond time resolution has been achieved with step-scan FT-IR absorbance difference spectroscopy (S2FT-IR Δ A TRS) and demonstrated by measuring Δ A spectra of fac-[Re(bpy)(CO)3Cl] and cis-[Os(bpy)2(CO)(4,4′-bpy)]2+ (bpy = 2,2′-bipyridine; 4,4′-bpy=4,4′-bipyridine) in CH3CN solution, following 355-nm laser excitation. In both complexes, the large shifts in (CO) to higher energy are consistent with the assignment that the lowest-energy excited states are metal-to-ligand charge transfer in nature. For [Os(bpy)2(CO)(4,4′-bpy)]2+, it is also possible to measure the excited-state decay kinetics, again with 10-ns resolution. In addition, Δ A bands are observed that are related to excited-state vibrations of the bipyridine ligands. Δ A spectra of good signal-to-noise ratio can be obtained for complexes with lifetimes as short as 10 ns.

In situ studies of metal–semiconductor interactions with synchrotron radiation

1998 ◽  
Vol 5 (3) ◽  
pp. 1050-1051
Author(s):  
D. E. Sayers ◽  
P. T. Goeller ◽  
B. I. Boyanov ◽  
R. J. Nemanich
Keyword(s):  
Synchrotron Radiation ◽  
Silicon Germanium ◽  
Signal To Noise Ratio ◽  
Thick Films ◽  
Strained Silicon ◽  
Reaction Products ◽  
Signal To Noise ◽  
In Situ Studies ◽  
And Performance

The capabilities and performance of a UHV system for in situ studies of metal–semiconductor interactions are described. The UHV system consists of interconnected deposition and analysis chambers, each of which is capable of maintaining a base pressure of approximately 1 × 10−10 torr. The deposited materials and their reaction products can be studied in situ with RHEED, XAFS, AES, XPS, UPS and ARUPS. Results from a study of the reaction of 0.7- and 1.7-monolayer-thick films of cobalt with strained silicon–germanium alloys are presented. The signal-to-noise ratio obtained in these experiments indicates that the apparatus is capable of supporting in situ EXAFS studies of ∼0.1-monolayer-thick films.

scholarly journals Direct Observations of the Heterogeneity of Supergiant Disks

1977 ◽  
Vol 4 (2) ◽  
pp. 405-405
Author(s):  
J. W. Harvey ◽  
C. R. Lynds ◽  
S. P. Worden
Keyword(s):  
Signal To Noise Ratio ◽  
Atmospheric Dispersion ◽  
Stellar Atmosphere ◽  
High Magnification ◽  
Specific Technique ◽  
Signal To Noise ◽  
Speckle Imaging ◽  
Direct Observations ◽  
Good Signal ◽  
Limb Darkening

Resolved images of the disks of the largest stars observed with the largest telescopes can be constructed using the class of techniques called speckle imaging. The observations must be made with narrow passbands (~ 10 nm), short exposures (~ 20 ms) compensation for atmospheric dispersion, high magnification and good signal-to-noise ratio. One specific technique applied to a Ori (Lynds et al., 1976) shows slight but apparently real differences in the images of the disk corresponding to low and high opacity in the stellar atmosphere which we interpret as due to temperature differences. There are also significant differences in the star’s diameter and/or limb darkening at the two different opacity wavelengths.

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