Laser Doppler vibrometer

About: Laser Doppler vibrometer is a research topic. Over the lifetime, 6319 publications have been published within this topic receiving 76068 citations.

Laser vibrometer for vibration measurements

Abstract: A laser diode (1) of a laser vibrometer emits light which is guided onto a polarization beam splitter (3) by a lens 2. A portion of the beam is guided through directly to an imaging lens (4) and a second portion is deflected onto a mirror (5). Quarter-wave plates (6) and (7) are arranged between the polarization beam splitter and respectively the lens or the mirror. The beam which is reflected on the mirror is guided completely through the polarization beam splitter onto a photodetector unit (8). The beam reflected by the object (9) to be measured, which swings in the direction (14), is also deflected to the photodetector unit. The output signal of the photodetector unit, the interference signal generated from the superposition of the two reflected beams, is supplied to an electronic evaluation equipment (10). The latter is also supplied with a signal of a current modulator (11) which, on the other hand, supplies the laser diode with modulated injection current via line (12). The distance between the imaging lens and the object to be measured forms an optical detour (13) which is considerably lengthened compared to the reference arm.

Frequency locking of a Nd:YAG laser using the laser itself as the optical phase modulator

Abstract: We report frequency locking of a Nd:YAG tunable laser to a 2000 finesse 87‐cm‐long Fabry–Perot cavity in air using the Pound–Drever technique. The novelty is that the necessary phase modulation of the beam is obtained using the laser directly instead of an external phase modulator (Pockels cell). The spurious relative amplitude modulation using this method was ∼3×10−5 with a modulation index β∼1 and the spectral density of the frequency difference between the laser and the cavity is below 1 mHz/√Hz in the region 1–500 Hz.

Laser power control

Abstract: A laser power control system is disclosed which detects the power of an emtted laser beam. The detection is preferably accomplished by splitting the beam using a beam splitter to form a detector laser beam which includes a limited portion of the beam. The beam is preferably split after polarization to obvate changes in detected power associated with polarization changes which can occur in the laser. The detector beam can be detected either continuously or intermittently, such as by using a chopping wheel which intermittently passes and interrupts the detector beam. The detected laser beam power signal is compared against a predetermined set point or preprogrammed time variable laser power profile thus allowing desired laser power to be achieved. The laser beam is also preferably equalized to achieve a more uniform cross-sectional laser power density. Laser beam equalizers are shown which disperse a laser beam into non-parallel rays which are passed through an optical channel, such as a reflective passage or optical fiber. The system provides laser beams having controlled and equalized laser power.