Continuous Wave Sources

Rapidly spinning neutron stars are the main source of continuous waves in the HF band accessible to earth-based interferometers and resonant bar detectors. When the neutron star can be observed using radio (or other) telescopes, the expected gravitational waveform can be inferred (up to small uncertainties) from observations of the spin period. In this case, the optimal data analysis strategy is matched filtering. The implementation may be slightly different than for burst sources, but the idea is the same. Successful detection of waves from these sources will rely on direct interaction between the radio astronomers and gravitational astronomers. 

Earth-motion-induced Doppler shifts, and intrinsic frequency evolution of the sources, will reduce the narrow-band signal-to-noise by spreading power across many frequency bins therefore, it is necessary to correct for these effects before performing the Fourier transform. The corrections can be implemented by a parametrized model in which one searches over a discrete set of points in the parameter space of corrections. The signal-to-noise ratio required for a confident detection depends on the number of points which must be considered in the search. 

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Terahertz, or far infrared spectroscopy, covers the frequency range from 0.1 to lOTHz (300 to 3cm ) where torsional modes and lattice vibrations of molecules are detected. It is increasing in use in many application areas, including analysis of crystalline materials. Several dedicated conunercial instruments are available which use pulsed terahertz radiation which results in better signal to noise than those using blackbody sources for radiation (and associated with the terminology far infrared spectroscopy). Work using extended optics of FTIR instrumentation as weU as continuous-wave source THz has also been recently reported. ... 

The lamps may be operated as continuous wave sources or be modulated or pulsed. EDLs have a poor stability or poor shelf life in some cases, but they have high intensities, produce narrow spectral lines, and are relatively inexpensive. 

LPPP derivatives have been extensively studied for their third-order NLO properties.An LPPP derivative, 125 (m-LPPP), was studied by TPEF method employing a continuous wave source in chloroform as wdl as in thin films. This compound is known to have effective extended conjugation of up to 12-monomeric units. At 769 nm, this compound showed an extraordinarily large TPA cross seaion value of 72 000 GM per repeat unit in solution. The two-photon luminescence was studied by varying the concentration of the solution from 6 x 10" to 5 x 10. The TPA cross section was found to be an intrachain phenomenon with no influence from increasing concentration. On cooling from 300 to 6 K, TPA cross section of the films of 125 was found to increase by a... 

Continuous wave (CW) lasers such as Ar and He-Ne are employed in conmionplace Raman spectrometers. However laser sources for Raman spectroscopy now extend from the edge of the vacuum UV to the near infrared. Lasers serve as an energetic source which at the same hme can be highly monochromatic, thus effectively supplying the single excitation frequency, v. The beams have a small diameter which may be... 

Population inversion is difficult not only to achieve but also to maintain. Indeed, for many laser systems there is no method of pumping which will maintain a population inversion continuously. For such systems inversion can be brought about only by means of a pumping source which delivers short, high-energy pulses. The result is a pulsed laser as opposed to a continuous wave, or CW, laser which operates continuously. 

Fig. 2. Maximum limits of average output power P 0 from power sources at average wattages or continuous wave (CW) where A is the soHd state B,...

The first successful application of the continuous wave (CW) He-Ne gas laser as a Raman excitation source by Kogelnik and Porto (14) was reported in 1963. Since that time, significant improvements in instrumentation have been continually achieved which have circumvented a great number of problems encountered with mercury lamp sources. The renaissance of Raman spectroscopy has also been due to improvements in the design of monochromators and photoelectric recording systems. 

A He-Ne continuous wave laser provides an 8-mW source of radiation at 6328 A. Calculate the intensity of the light in photons/sec. The light beam has a 3 mm diameter. How many hours would be required to... 

Historically, this has been the most constrained parameter, particularly for confocal laser scanning microscopes that require spatially coherent sources and so have been typically limited to a few discrete excitation wavelengths, traditionally obtained from gas lasers. Convenient tunable continuous wave (c.w.) excitation for wide-held microscopy was widely available from filtered lamp sources but, for time domain FLIM, the only ultrafast light sources covering the visible spectrum were c.w. mode-locked dye lasers before the advent of ultrafast Ti Sapphire lasers. 

In practical application, Raman sensors exclusively use frequency-stabilised laser sources to compensate for the low intensity of the Raman radiation. For Raman sensors, prevalently compact high-intensity external cavity laser diodes are used, operated in CW (continuous wave) mode. These diode lasers combine high intensity with the spectral stability required for Raman applications and are commercially available at various wavelengths. 

By employing a laser for the photoionization (not to be confused with laser desorption/ ionization, where a laser is irradiating a surface, see Section 2.1.21) both sensitivity and selectivity are considerably enhanced. In 1970 the first mass spectrometric analysis of laser photoionized molecular species, namely H2, was performed [54]. Two years later selective two-step photoionization was used to ionize mbidium [55]. Multiphoton ionization mass spectrometry (MPI-MS) was demonstrated in the late 1970s [56—58]. The combination of tunable lasers and MS into a multidimensional analysis tool proved to be a very useful way to investigate excitation and dissociation processes, as well as to obtain mass spectrometric data [59-62]. Because of the pulsed nature of most MPI sources TOF analyzers are preferred, but in combination with continuous wave lasers quadrupole analyzers have been utilized [63]. MPI is performed on species already in the gas phase. The analyte delivery system depends on the application and can be, for example, a GC interface, thermal evaporation from a surface, secondary neutrals from a particle impact event (see Section 2.1.18), or molecular beams that are introduced through a spray interface. There is a multitude of different source geometries. 

H. Schnitzler, U. Frohlich, T.K.W. Boley, A.E.M. Clemen, J. Mlynek, A. Peters, and S. Schiller, All-solid-state tunable continuous-wave ultraviolet source with high purity and frequency stability. Applied Optics 41(33), 7000-7005 (2002). 

So far presented results are connected with so-called steady-state spectroscopy. Conventionally studied steady state or CW (continuous-wave) liuni-nescence is a process where the excitation sources pump the sample at constant intensity over a time necessary to perform the measurement. The end result is... 

Fig. 1 Schematic of a setup for in situ steady-state X-ray photodiffraction using continuous wave and pulsed excitation sources...

Muchall et al. (98CC238) have recently investigated the gas-phase thermolysis of 2,5-dihydro-2,2-dimethoxy-2,5,5-trimethyl-l//-l,2,4-oxadiazole (75) by PE spectroscopy. Decomposition of 75 was induced by means of a continuous wave (CW) C02 laser as directed heat source at 26 W, which corresponds to a temperature of 500 50°C. When the PE spectra of acetone, tetramethoxyethene, and dimethyl oxalate were subtracted from the pyrolysis spectrum, a sim-ple spectrum remained that could be identified as that of dimethoxycarbene. Thermolysis in solution (94JA1161) had shown formation of tetramethoxyethene, and FVP experiments (92JA8751) gave dimethyl oxalate, both of which arise from the common precursor, dimethoxycarbene. Thermolysis of oxadiazolines similar to 75 in solution affords dialkoxycarbenes via an intermediate carbonyl ylide (94JOC5071). 

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