Direct measurement of longitudinal velocity by Doppler phase-shifting holography

3D velocity measurement by a single camera using Doppler phase-shifting holography

“…Thus, it has been proved that a Doppler phase-shifting holography can be used for the measurement of the longitudinal velocity. Moreover, the surface profile of the concave mirror was reproduced from the phase data of the digital holography and the rms error to the R = 30 mm profile is only 3.27 nm [33]. This is the evidence that Doppler phaseshifting technique is capable of measuring the 3D position and the longitudinal velocity simultaneously.…”

“…It should be noted that as any part of the concave mirror is travelling at the same speed, choice of any pixel may give the similar spectrum. A clear peak of the Doppler beat is found at 386.7 Hz, which corresponds to υ O = 99.4 µm s −1 with the error of 0.6% to the given longitudinal velocity [33]. Thus, it has been proved that a Doppler phase-shifting holography can be used for the measurement of the longitudinal velocity.…”

“…This is the evidence that Doppler phaseshifting technique is capable of measuring the 3D position and the longitudinal velocity simultaneously. As the fundamental measurement technique has been proved to work in the previous study [33], the actual measurement of the 3D velocity is carried out by the experimental setup shown in figure 2. The Japanese 5 yen coin, whose diameter is about 22 mm, is used as a target object and is traversed at a constant speed at a specific angle.…”

“…Yet, as the beat frequency of the Doppler beat is proportional to the velocity difference between the object light and the reference light, the longitudinal velocity of an object can be measured by the beat frequency of the Doppler beat. In order to prove this, Ninomiya et al [33] measured the longitudinal velocity of a concave mirror travelling at a constant speed by a Doppler phase-shifting holography.…”