Continuous waves

Although continuous wave NMR is sufficient for naturally abundant nuclei with strong magnetic moments such as hydrogen, fluorine and phosphorous, the study of low abundance nuclei and/or weak magnetic moments such as carbon 13 or silicon 29 requires pulse NMR. 

Each experimential values and the calculative values in Fig.7 and Fig.9 are almost corresponding except for the region of the echo height F/B rapidly decreases. This reason is thought that the experiment using a pulse wave but the calculative using a continuous wave. 

Much of the previous section dealt with two-level systems. Real molecules, however, are not two-level systems for many purposes there are only two electronic states that participate, but each of these electronic states has many states corresponding to different quantum levels for vibration and rotation. A coherent femtosecond pulse has a bandwidth which may span many vibrational levels when the pulse impinges on the molecule it excites a coherent superposition of all tliese vibrational states—a vibrational wavepacket. In this section we deal with excitation by one or two femtosecond optical pulses, as well as continuous wave excitation in section A 1.6.4 we will use the concepts developed here to understand nonlinear molecular electronic spectroscopy. 

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... 

Boyd G T, Shen Y R and Hansch T W 1986 Continuous-wave second-harmonic generation as a surface microprobe Opt. Lett. 11 97-9... 

McLauchlan K A 1990 Continuous-wave transient electron spin resonance Modern Pulsed and... 

Continuous-Wave Electron Spin Resonance ed L Kevan and M Bowman (New York Wiley) oh 7, pp 285-363... 

Allgeler J, DIsselhorst A, Weber R, Wenckebach W and Schmidt J 1990 High-frequency pulsed electron spin resonance Modern Pulsed and Continuous-Wave Electron Spin Resonance ed L Kevan and M K Bowman (New York Wley) ch 6, pp 267-83... 

In this approach one uses narrow-band continuous wave (cw) lasers for continuous spectroscopic detection of reactant and product species with high time and frequency resolution. Figure B2.5.11 shows an experimental scheme using detection lasers with a 1 MFIz bandwidth. Thus, one can measure the energy spectrum of reaction products with very high energy resolution. In practice, today one can achieve an uncertainty-limited resolution given by... 

Soper S A and Legendre B L Jr 1998 Single-molecule detection in the near-IR using continuous-wave diode laser... 

Lasing substances Physical state Laser wavelength (nm) Pulse length or continuous wave Typical maximum power output (watts)... 

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. 

The efficiency of a helium—neon laser is improved by substituting helium-3 for helium-4, and its maximum gain curve can be shifted by varying the neon isotopic concentrations (4). More than 80 wavelengths have been reported for pulsed lasers and 24 for continuous-wave lasers using argon, krypton, and xenon lasing media (111) (see Lasers). 

L. Kevan and M. K. Bowman, eds.. Modem Tubed and Continuous-Wave Tkctron Spin John Wiley Sons, Inc., New York, 1990. 

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,...

Nonlinear refraction phenomena, involving high iatensity femtosecond pulses of light traveling in a rod of Tfsapphire, represent one of the most important commercial exploitations of third-order optical nonlinearity. This is the realization of mode-locking ia femtosecond Tfsapphire lasers (qv). High intensity femtosecond pulses are focused on an output port by the third-order Kerr effect while the lower intensity continuous wave (CW) beam remains unfocused and thus is not effectively coupled out of the laser. 

New impetus was given to photomedicine by development of lasers that are compatible with the clinical environment. These include HeNe, Ar ion, mby, and tunable dye lasers operating in the continuous wave (cw) mode. Prior to the advent of lasers in medicine, only the treatment of newborn jaundice, and the appHcation of long wavelength uv irradiation in conjunction with adininistration (or topical appHcation) of psoralen class sensitizers to treatment of skin diseases (86), principally psoriasis, were clinically important phototherapies. 

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