physics-lasertech-2019-keynote

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allied
academies
April 15-16, 2019 | Frankfurt, Germany
Applied Physics & Laser, Optics and Photonics
International Conference on
Page 15
Materials Science and Nanotechnology | Volume: 3
By understanding the Fabry-Perot resonator, one
can better understand the laser that oscillates
in such a resonator. Recently, we clarified various
aspects of the Fabry-Perot resonator, namely the
existenceoftwocounter-propagatingmodesateach
resonance frequency and polarization, the relation
between mode profiles and airy distributions, the
Lorentzian and Airy linewidths and finesses, and
the spectral response under frequency-dependent
mirror reflectivities and under intrinsic gain or loss.
Based on the assumption that stimulated emission
occurs in phase with the incident field, whereas
spontaneous emission occurs under an arbitrary
phase difference with respect to an incident field,
Lax and Haken derived quantum-mechanically the
Schawlow-Townes laser linewidth and predicted
its narrowing by a factor of two around the laser
threshold, and Henry predicted its re-broadening
due to amplitude-phase coupling, resulting in the
α-factor. However, Maxwell’s equations suggest
that both stimulated and spontaneous emission
would violate the law of energy conservation. We
have shown that the phase of the emitted field is
90° in lead of the incident field. When combining
Weisskopf’s idea that vacuum fluctuations trigger
spontaneous emission with Einstein’s semi-
classical rate-equation approach to Planck’s law
of blackbody radiation, a direct consequence is
that an optical mode contains a vacuum energy
of hν. This result contradicts with Heisenberg’s
proof that a quantum-harmonic oscillator contains
a zero-point energy of ½ hν. We show that this
factor-of-two difference and the factor-of-two
narrowing of the laser linewidth have the same
origin. Finally, we derive straight-forwardly the
general laser linewidth and the Schawlow-Townes
approximation in a semi-classical manner.
Speaker Biography
Markus Pollnau received MSc and PhD in physics from the University of
Hamburg, Germany in 1992 and the University of Bern, Switzerland in
1996, respectively. In 2004, he became a full professor at the University
of Twente, The Netherlands. Currently, he works as a full professor
in photonics at the University of Surrey, UK. He has contributed to
more than 600 reviewed journal and international conference papers
and 14 book chapters. He served as program and general co-chair
of the conference on Lasers and Electro-Optics (2006/2008) and
the conference on Lasers and Electro-Optics Europe (2009/2011),
inaugurated the Europhoton conference (2004), and served as topical
editor for the Journal of the Optical Society of America B and Laser
Physics Letters. He is a fellow of the Optical Society of America and the
European Physical Society.
e:
Markus Pollnau
University of Surrey, UK
The laser linewidth - Fairy tales and physical evidence