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Buchbeiträge:

F. Bammer:
"Single Crystal Photo-Elastic Modulators";
in: "High-Power and Femtosecond Lasers: Properties, Materials and Applications", F. Columbus (Hrg.); herausgegeben von: Paul-Henri Barret, Michael Palmer; Nova Science Publishers, Inc, 2009, ISBN: 978-1-60741-009-6, S. 71 - 123.



Kurzfassung deutsch:
Classical photo-elastic modulators (PEM) modulate the polarization of a light beam and are mainly used in ellipsometry. They are usually made of a piece of optical glass which is glued to a quartz-crystal, which is adjusted in an elaborate process to oscillate in a longitudinal mode. Polarized light traveling through the glass will experience a modulated polarization due to stress induced birefringence. The voltage needed to drive such a PEM is by two orders of magnitude lower than in case of electro-optic devices.
A Single Crystal Photo-Elastic Modulator (SCPEM) can now be made of one single crystal. For visible light (VIS) and the near infrared (NIR) the best choice is LiTaO3 out of the crystal group 3m and for the mid infrared (MIR) one can use GaAs, ZnSe, or CdTe, all exponents of the crystal group 4_3m. Within a special holder, in which the desired mechanical eigenmode can freely move, an alternating voltage with a corresponding frequency is applied to electrodes on the crystal. Due to the piezo-electric behavior, which is only found together with electro-optic properties, the crystal will finally end in a strong resonant oscillation that needs only very little electrical power. Due to the photo-elastic effect, inherent to all transparent materials, an additional, artificial, modulated birefringence is generated, which will strongly influence the polarization of light. Together with a polarizer it is easy to generate a transmission course that oscillates between 0 and 1 with rather fast transitions.
It is now obvious tot replace classical PEMs in ellipsometry with SCPEMs. Besides that there are applications in high power laser technology like time-multiplexing, Q-switching, pulse picking, active mode coupling, and optical switching.
This contribution will explain in detail the theory of SCPEMs for both types mentioned above. This covers crystal-optics, piezo-electricity, the electro- and elasto- optic effect, the description of the resonant behavior and a detailed discussion on the effect on polarized light based on Müller calculus. Further all possible applications with assets and limitations will be covered such that at the end the reader will have a complete survey on this new technology.

Kurzfassung englisch:
Classical photo-elastic modulators (PEM) modulate the polarization of a light beam and are mainly used in ellipsometry. They are usually made of a piece of optical glass which is glued to a quartz-crystal, which is adjusted in an elaborate process to oscillate in a longitudinal mode. Polarized light traveling through the glass will experience a modulated polarization due to stress induced birefringence. The voltage needed to drive such a PEM is by two orders of magnitude lower than in case of electro-optic devices.
A Single Crystal Photo-Elastic Modulator (SCPEM) can now be made of one single crystal. For visible light (VIS) and the near infrared (NIR) the best choice is LiTaO3 out of the crystal group 3m and for the mid infrared (MIR) one can use GaAs, ZnSe, or CdTe, all exponents of the crystal group 4_3m. Within a special holder, in which the desired mechanical eigenmode can freely move, an alternating voltage with a corresponding frequency is applied to electrodes on the crystal. Due to the piezo-electric behavior, which is only found together with electro-optic properties, the crystal will finally end in a strong resonant oscillation that needs only very little electrical power. Due to the photo-elastic effect, inherent to all transparent materials, an additional, artificial, modulated birefringence is generated, which will strongly influence the polarization of light. Together with a polarizer it is easy to generate a transmission course that oscillates between 0 and 1 with rather fast transitions.
It is now obvious tot replace classical PEMs in ellipsometry with SCPEMs. Besides that there are applications in high power laser technology like time-multiplexing, Q-switching, pulse picking, active mode coupling, and optical switching.
This contribution will explain in detail the theory of SCPEMs for both types mentioned above. This covers crystal-optics, piezo-electricity, the electro- and elasto- optic effect, the description of the resonant behavior and a detailed discussion on the effect on polarized light based on Müller calculus. Further all possible applications with assets and limitations will be covered such that at the end the reader will have a complete survey on this new technology.

Schlagworte:
Photo-elastic Modulators, LiNbO3, LiTaO3, Q-switching, Ellispometry

Erstellt aus der Publikationsdatenbank der Technischen Universitšt Wien.