Corridor of EEIC, The University of Tokyo

Laser Physics, Laser Sensing, Diagnostics of Electric Power Apparatus：Takashi Fujii

Development of innovative laser sensing techniques and their application to high voltage engineering

Lasers are characterized by their high spatial coherence, which allows a laser beam to stay narrow over great distances, high temporal coherence, which allows them to emit light with a very narrow spectrum, and high peak intensity. In particular, intense lasers with femtosecond pulse widths produce various new physical phenomena due to their strong nonlinear effects. In this laboratory, we are investigating these physical phenomena and working on various applications of the laser. I direct HV lab. in collaboration with Prof. Akiko Kumada and Assistant Prof. Masahiro Sato.

Non-contact, non-invasive measurement of electric field using ultrashort laser pulses

The establishment of a non-contact, non-invasive technique for measuring electric fields is a long-cherished dream for researchers working with electrical discharges and insulation. When a laser beam is focused into an isotropic material such as a gas, the interaction between the external electric field and the laser’s optical field generates a second harmonic due to third-order nonlinear optical effects. In addition, the use of ultrashort intense laser pulses with pulse widths in the femtosecond range leads to a variety of nonlinear phenomena. We are investigating these nonlinear phenomena and developing non-contact, non-invasive techniques for measuring the three-dimensional distribution of electric fields using these phenomena.

Diagnostics of Electric Power Apparatus by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is an attractive tool for the in-situ and remote measurement of elements attached on or contained in a target. In this method, the laser beam is focused on the target to produce plasma, of which emission is analyzed spectroscopically. We are developing methods of measurement and diagnostic for the application to such as electric power equipment using LIBS. We have succeeded in developing a method to remotely diagnose the degradation of polymer insulators by measuring the content of the insulators with a distance of 10 meters.

Elucidation of Arc Discharge by Wave-front Sensor

SF6 gas, which has a high global warming potential, is mainly used in gas circuit breakers in power grids. In order to develop alternative gases, it is necessary to understand the arc extinguishing phenomena in SF6 and other gases. Laser wavefront sensors provide us interesting insight of arc discharge. For example, the Shack-Hartmann sensor, which consists of a microlens array and can measure the spatial derivative of the wavefront, can be used to measure the electron density in an arc discharge. We have also succeeded in visualising the gas turbulence structure in the arc by using a laser wavefront measurement system with a band-pass spatial filter. The results show that SF6 has the finest turbulent structure, followed by CO2 and Air, and that the high arc extinguishing performance of SF6 is due to the increased energy loss caused by the fine turbulence.