Prototype Measuring Instruments

designed and assembled by the Optoelectronics Group

The Optoelectronics Group of the Università di Pavia owns a 15+ years experience in the field of optoelectronics instrumentation/sensors, and contributed to the study and the development of new types of sensing schemes and instruments, mainly in the field of laser interferometry and vibrometry.

The Optoelectronic Group has pioneered the principle of self-mixing interferometry, and it has recently designed and built two new sensors for the measurement of vibrations and displacements of remote diffusive targets, based on the self-mixing effect in laser diodes.

Distinctive features of the self-mixing approach are:

The Instruments

Two prototype instruments have been built: a LASER VIBROMETER and a LASER INTERFEROMETER

Laser Vibrometer
download Vibrometer datasheet (PDF, 622 Kb)

Laser Interferometer
download Interferometer datasheet (PDF, 179 Kb)

 

Description. The new Laser Vibrometer is based on the self-mixing interferometric effect, which is different in principle from the conventional Laser Doppler Velocimetry (LDV) technique. The instrument allows easy and accurate non-contact vibration measurements on all rough and diffusive surfaces (e.g.: plastic, rubber, unfinished metal, paper, etc.). It provides an analog electrical output which is a replica of the target displacement, in a frequency range 0.01 Hz ÷ 70 kHz. The new Laser Vibrometer has a high sensitivity that allows correct operation even for very weak intensities of light backscattered by the target.
Applications.
  • Non-contact measurement of vibration displacement
  • Material analysis
  • Vibration measurement without mass-loading on small, soft and delicate structures
  • Loudspeaker testing
  • Piezoceramic testing
  • Modal analysis
  • On-line process control in industrial plants
  • Quality tests

Performance
Output signal responsivity 10 mV/µm
Noise equivalent vibration 90 pm/(Hz)1/2
Maximum measurable vibration 300 µm
Bandwidth 0.01 Hz ÷ 70 kHz
Working distance 50 ± 8 cm
Laser power 17 mW
Laser wavelength 800 ± 5 nm
Laser safety class III B

download Vibrometer datasheet (PDF, 622 Kb)

 

Laser Interferometer for operation
on Diffusive Surfaces
download datasheet (PDF, 179 Kb)
Description. The new Laser Interferometer is based on the self-mixing interferometric effect and it allows non–contact displacement measurements without the need of placing mirrors or corner cubes on the moving target. A novel speckle-tracking system allows operation on diffusive surfaces, overcoming the problem of signal fading. The self-mixing interferometric configuration is self-aligning, and no complicate and time-consuming alignment procedure shall be carried out before measurement takes place. The displacement is shown by an indicator in metric unit, and it is also provided as a digital output on a RS232 port.
Applications.
  • Non-contact incremental measurement of displacement
  • Machinery tool calibration
  • Vibration measurement (amplitudes from few µm to several cm)
  • On–line process control in industrial plants
  • Quality tests

Performance
Resolution 0.4 µm
Accuracy 10-5
Working distance 0÷1 m
Maximum target speed 10 cm/s
Laser power 30 mW
Laser wavelength 785 ± 5 nm
Laser safety class III B

download Interferometer datasheet (PDF, 179 Kb)

Instruments Availability

Thanks to the features of the self-mixing interferometric approach, the proposed instruments offer very good performance using a simple optical set-up, and hence they can be built at a low cost.

Instruments with custom configuration/performance can be made available to interested Research Centers, Universities and Companies within the frame of a research agreement with the Optoelectronics Group.

Contact:

Prof. Silvano Donati (Head of Optoelectronics Group)
Dipartimento di Elettronica - Università di Pavia
Via Ferrata 1, I-27100 Pavia, Italy
silvano.donati@unipv.it
Tel. +39 0382 505 204
Fax +39 0382 422 583

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