Dentro da programação do evento alusivo ao Dia Internacional da Luz (celebrado em 16 de maio), o Seminário de Óptica da próxima terça-feira, 15 de maio (14 horas, no auditório do Departamento de Física/UFPE) será especial, contado com duas palestras de uma hora cada, apresentadas pelo Prof. Dr. Walter Margulis (Royal Institute of Technology, Suécia) e pelo Prof. Dr. Raman Kashyap (Department of Engineering Physics and Department of Electrical Engineering, Univ. Polytechnique Montreal, Canadá).
14h00 às 15h00: Prof. Dr. Walter Margulis
Título: Sensing and measurring with optical fibers
Resumo: Optical fibers have been used for sensing and measurement for decades. Recently, however, the use of fibers in industrial environments became much more accepted. Some of the driving forces behind this development include the concept that machines must also tell us how they are doing, the introduction of new classes of materials, and the need for increased efficiency in industrial processes, for example at high temperature or under the sea. All these open new opportunities for the use of fibers. Likewise, the needs for monitoring the environment, for safety and for human health are examples of challenges that require advanced sensing. The known advantages of optical fibers are then increasingly explored in monitoring temperature, pressure, movement, distance, acceleration, electric and magnetic fields and current and many other parameters. In this seminar, we will discuss possibilities opened by the use of advanced fibers and techniques for sensing and measurement, and give some examples of recent work in the area.
15h00 às 16h00: Prof. Dr. Raman Kashyap
Título: The Raman effect re-visited: creating new light from old photons
Resumo: Sir Chandrashekhara Venkata Raman won the Nobel prize in 1930, two years after his discovery of the effect bearing his name. The very weak spontaneous Raman effect, as it came to be known, is the phenomenon of frequency-shifted scatter of incident light in a material. This instantaneous effect with a response time of fs, generates new radiation from light interacting with the rich spectrum of periodic changes in the polarisability induced by molecular vibrations or resonant electronic excitations. Light interaction over a long length, or with the use of high optical intensity, can lead to efficient frequency conversion by stimulated Raman scattering (SRS). More recently, the long length has been shrunk using a resonator in which the Raman-shifted photons remain trapped by the cavity Q, far longer than the characteristic Raman response time of the material. These « old and tired» photons generate SRS leading to multi-wavelength Raman lasing, despite the weak Raman gain.
Recent progress in distributed feedback fibre Bragg gratings (DFB-FBGs) has transformed the extremely weak spontaneous Raman effect through the powerful SRS mechanism to generate any desired single-frequency in compact format. Taming the interaction for high efficiency has been a challenge that has only recently been solved at Polytechnique Montreal. Understanding the theory of only 10’s of cm long, DFB-FBG Raman fibre lasers and the interaction with stimulated Brillouin scattering were the key towards this goal.
The presentation will discuss our recent progress in high quality SRS-DFB-FBG lasers for single mode, single frequency and polarisation operation at virtually any wavelength, with thresholds of only 100’s mW for semiconductor diode laser pumping, and the possibility of designing random-FBG Raman lasers with any desired randomness.
