Continuous wave Doppler

Fig. 3. Continuous wave Doppler-free two-photon spectra of hydrogen and deuterium 1S-2S [11].

Berger M, Haimowitz A, Van Tosh A, et al. Quantitative assessment of pulmonary hypertension in patients with tricuspid regurgitation using continuous wave Doppler ultrasound. J Am Coll Cardiol 1985 6(2) 359—65. 

Among anatomic variants, duplication of veins, especially at the femoral (20%) and popliteal (35%) level, is common. In this instance, veins are generally smaller than in a single system and may be potential source of error at continuous-wave Doppler analysis. 

If instead of transmitting a continuous wave, the Doppler system transmits a sawtooth frequency-modulated (FM) wave, both the velocity and the instantaneous distance betw the missile and the ground station can be detd simultaneously. This ptinciple is explained in Ref 2, p 166 and illustrated in the graph. The FM radar system is capable of measuring accurately only short distances (Ref 2, p 166)... 

Laser spectroscopy of the 1S-2S transition has been performed by Mills and coworkers at Bell Laboratories (Chu, Mills and Hall, 1984 Fee et al, 1993a, b) following the first excitation of this transition by Chu and Mills (1982). Apart from various technicalities, the main difference between the 1984 and 1993 measurements was that in the latter a pulse created from a tuned 486 nm continuous-wave laser with a Fabry-Perot power build-up cavity, was used to excite the transition by two-photon Doppler-free absorption, followed by photoionization from the 2S level using an intense pulsed YAG laser doubled to 532 nm. Chu, Mills and Hall (1984), however, employed an intense pulsed 486 nm laser to photoionize the positronium directly by three-photon absorption from the ground state in tuning through the resonance. For reasons outlined by Fee et al. (1993b), it was hoped that the use of a continuous-wave laser to excite the transition would lead to a more accurate determination of the frequency interval than the value 1233 607 218.9 10.7 MHz obtained in the pulsed 486 nm laser experiment (after correction by Danzmann, Fee and Chu, 1989, and adjustment consequent on a recalibration of the Te2 reference line by McIntyre and Hansch, 1986). 

The interval 235i — l3,S i has been measured by the method of two-photon, Doppler-free excitation in two experiments [13] [14], We will detail the latter experiment, which employs continuous-wave excitation. 

In the early 1980s, clinical echocardiography was performed with a sector scanner, a stand-alone Doppler unit capable of a pulsed and continuous-wave mode operation, a spectral analyser with high temporal resolution and an in-house black box which allowed EKG display along with the spectra (Gramiak and Holen 1984). Due to the fact that small gas bubbles dissolve rapidly in blood, the next aim was the production of agents small enough to traverse the pulmonary capillary bed. 

Continuous-wave (CW) Doppler waveforms are commonly used in conjunction with segmental pressures or ABIs. Waveforms can help in identifying the location of arterial disease in the lower extremity. Waveforms are usually taken from the common femoral, superficial femoral, popliteal, dorsalis pedis, and posterior tibial arteries and recorded on a strip chart recorder. Qualitative analysis of the waveforms is performed to identify abnormalities in the arterial circulation. The presence of triphasic waveforms at any level indicates absence of a hemodynamically significant arterial lesion proximal to that level. Attenuated waveforms that have lost their triphasic appearance indicate an arterial stenosis proximally. 

Today we have at our disposal a wide arsenal of different methods for Doppler-free saturation spectroscopy. It appears likely that future progress will come not so much from the development of still further techniques, but rather from an extension of the wavelength range of highly monochromatic tunable continuous wave laser sources, in particular towards the ultraviolet, where many interesting transitions remain unexplored. 

The Doppler meter may be used wherever small particulate solids, bubbles or droplets are dispersed in the fluid and are moving at essentially the same velocity as the fluid stream which is to be metered. A continuous ultrasonic wave is transmitted, again at an acute angle to the wall of the duct, and the shift in frequency between the transmitted and scattered waves is measured. This method of measurement of flowrate is frequently used for slurries and dispersions which present considerable difficulties when other methods are used. 

For simplicity, suppose that we have an emission spectrum consisting of a single, predominantly Doppler-broadened line. This spectrum may be taken as an approximation to the case of widely separated and nonoverlapping lines of equal intensity. Again for simplicity, now consider the typical emission spectrum to be continuous, not sampled. Thus q(x) is given by q(x) = q0 exp( —x2) for a typical line, where q0 is the peak height. We have chosen the abscissa to be measured in either wavelength or wave number relative to a typical line center. For illustrative purposes only, the x interval for the observation is taken to be 2 Ax. If the line is centered in this interval at x = 0, we can never have q(x) < exp ( — Ax2). 

Helioseismic waves are detected by measuring the Doppler shift of lines in the solar spectrum due to vertical motion of the Sun s surface along the line of sight. With appropriate data-reduction techniques, the frequencies for global oscillations can be determined to an accuracy of 5 ppm. This extreme accuracy requires long-term, continuous observations that are best done by spacecraft such as the joint ESA/NASA SOHO spacecraft, which observes the Sun from the Lagrangian point where the Earth gravity balances that of the Sun. 

Doppler ultrasonic flowmeters depend upon the reflection of a continuous ultrasonic wave (frequency 0.5-10 MHz) from particulate matter (scatterers) contained in the fluid. Hence they may be used to monitor the rate of flow of dirty liquids. The transducer involved can act both as transmitter and receiver and is generally of the clamp-on type (Fig. 6.4). If the scatterers can be assumed to be moving at the velocity of the liquid, then the volumetric rate of flow Q is related to the Doppler frequency shift AtoD by ... 

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