Dear Steve:
I read the news item in Laser Focus World [p. 18, November 2010] of the femtosecond news section, entitled "Laser pulse filaments produce Hawking radiation."
I am sorry to say the optical radiation observed by researchers at Università degli Studi di Milano, INFN sezione di Milano, Università dell'Insubria, and Università di Milano-Bicocca in Italy and Heriot-Watt University in Edinburgh, Scotland using a fs/ps laser pulse to create filaments in glass and observed at 90° to the laser path, [which is] attributed to Hawking radiation is wrong. They stated that "...self phase modulation and four wave mixing (observed previously in glass in three seminal papers by Albano and Shapiro, PRL 24,592,584,1219(1970) does not occur at 90 deg..." This is true; however, the forward supercontinuum radiation can scatter by elastic light scattering at 90° from Rayleigh, Brillouin, and/or depolarizer wing scattering. This note questions the origin to Hawking radiation, and recent observation attributes to light scattering from forward supercontinuum light. See photo enclosed of SC.
Dr. Robert R. Alfano
Distinguished Professor, Department of Physics; Director, Institute for Ultrafast Spectroscopy and Lasers, The City College of New York; e-mail: [email protected];www1.ccny.cuny.edu/ci/iusl
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