ABSTRACT
We present a compact optoacoustic laser Doppler velocimetry method that utilizes the self-mixing effect in a RF-excited CO(2) laser. A portion of a Doppler-shifted laser beam, produced by irradiating a single wavelength laser beam on a moving object, is mixed with an originally existing laser beam inside a laser cavity. The fine change of pressure in the laser cavity modulated by the Doppler-shifted frequency is detected by a condenser microphone in the laser tube. In our studies, the frequency of the Doppler signal due to the optoacoustic effect was detected as high as 50 kHz. Our measurements also confirmed that the signal varied linearly with the velocity of the external scatterer (the moving object) and the cosine of the angle between the laser beam and the velocity vector of the object.
ABSTRACT
In this study, wavelength-tunable and pulse-width variable Fourier domain mode-locking lasers were developed with a repetition rate of 60.9 kHz. A spectral laser tuning range of over 100 nm was achieved by tuning the offset voltage to a fiber Fabry-Perot tunable filter (FFP-TF). The pulse width variation was achieved with amplitude modulation of the driving voltage to the FFP-TF. The pulse width ranged from 6.2 µs to 55 ns. The linewidth of the laser changed, from 0.109 to 0.083 nm, according to the pulse width variation.
