Polytec Scanning Laser Vibrometer
Non- contact laser Doppler vibrometer analysis of structural vibrations.
Laser Doppler vibrometry (LDV) is a non-contact vibration measurement technique using the Doppler effect. LDV permits the measurement of hot, miniature or soft surfaces, even under water, without mass-loading. Polytec vibrometers are eye-safe Class 2 laser instruments, use a low-power Helium-Neon laser, and can operate at distances of hundreds of meters.
Laser vibrometers are typically two-beam interferometric devices that detect the phase difference between an internal reference and the measurement beam. The measurement beam is focused on the target and scattered back to the interferometer. The heterodyne principle used in Polytec vibrometers generates an FM carrier to provide the directional information, and also opens the possibility of digital traceable vibrometry.
Per ANSI requirements, laser manufacturers must classify lasers according to their potential to cause biological damage and the level of hazard inherent in the system. The classification system is based on laser output or power, wavelength, exposure duration, and emergent beam radiant exposure. (1)
CLASS 1. These lasers basically are exempt from the requirements of the laser safety program because the risk of hazard to the operator during normal operation is essentially nonexistent. Lasers in this category include those that operate laser printers and compact disc players.
CLASS 2. Lasers in this category emit energy in the visible range (ie, 400 nm to 700 nm). Laser energy produced by class 2 lasers may be viewed for very brief periods of time but may present potential hazards to the eyes if viewed directly for long periods of time. The light emitted generally is so bright that it is difficult to look into the beam for an extended period of time. The helium neon (HeNe) aiming beam used coaxially with invisible lasers is considered a class 2 laser, as are the laser pointers used in professional presentations.
CLASS 3. These lasers are medium-powered systems that require measures to prevent eye exposure. Class 3a lasers include systems that normally would not produce a hazard but are dangerous if viewed using collecting optics (ie, microscopes). The power range is 1.0 mW to 5.0 mW. Class 3b lasers are hazardous if viewed directly by the naked eye for longer than .25 seconds. Some ophthalmology lasers are class 3b lasers.
CLASS 4. Most of the lasers used in surgery are class 4 lasers. These lasers can cause damage not only to eyes but to skin, as well as present a fire hazard. Specific safety measures must be ha place before class 4 lasers are operated.
A new classification scheme, which already has been approved by the FDA and the International Electrotechnical Commission, probably will be introduced when ANSI revises its standards. The new classes--1m, 2m, and 3r--will further delineate the danger potential of medical and industrial lasers.
Laser energy is light energy. All class 3 and class 4 lasers are considered to be nonionizing, which means that laser energy does not cause molecular changes to the tissue of the operator or others in proximity. A pregnant staff member or physician need not fear that laser energy will cause harm to her fetus. Beam-related safety hazards include eye injuries, fire and thermal injuries, and smoke plume. Electrical hazards are a nonbeam-related hazard.