Christopher P. Yakymyshyn

Optical transducer and method of use

An optical transducer, such as used in an ultrasound system, includes a signal laser which generates an optical signal the frequency of which varies in correspondence with acoustic energy incident on the transducer. An optical cavity in the signal laser is disposed such that incident acoustic energy causes compression and rarefaction of the optical cavity, and this displacement varies optical frequency generated by the laser. A laser pump coupled to the lasing medium is adapted to apply selected levels of excitation energy appropriate to the generation and detection of acoustic pulses. The signal laser alternatively is adapted such that the refractive index of the optical cavity is varied in correspondence with the incident acoustic energy to modulate the optical frequency of the light generated by the signal laser. A piezoelectric device is disposed to receive the incident acoustic energy and generate a corresponding electrical signal that is applied to an electro-optic cell in the optical cavity, or alternatively, to conductors to generate an electric field across the lasing medium.

Optical detection of ultrasound with a microchip laser

A novel optical ultrasonic detector that relies on frequency modulation of a microchip laser is proposed and demonstrated. When the laser is placed in a time-varying acoustic field, the microchip laser cavity length is periodically modulated, creating a frequency-modulated optical output in which the frequency shift is linearly proportional to the acoustic-wave amplitude. With a confocal Fabry-Perot slope filter and a Nd:YAG microchip laser operating at 1.06 microm, a detector response of 7.5 MHz/kPa was measured at an acoustic frequency of 7.75 MHz. A one-dimensional acoustic model is developed to explain the observed detector performance.

Temperature sensor and extensometer

A thermometer and extensometer for cables and conductors is described. The travel time of one or more acoustic signals along a conductor is used to determine the temperature along the conductor and the length of the conductor. The acoustic frequency is selected to minimize temporal dispersion of the propagating acoustic energy. The technique can be used to measure the temperature and sag of an overhead power line, the temperature of the windings in a transformer, or the temperature of the central conductor in a coaxial power cable.