Electromagnetic coupling through apertures and shielding
effectiveness of a metallic enclosure housing electro-optic pockels cell in a
high power laser system
Affiliations: [a] Laser Electronics Support Division, Raja Ramanna
Centre for Advanced Technology, Indore, India | [b] Atomic and Molecular Physics Division, Bhabha Atomic
Research Centre, Mumbai, India | [c] Beam Electronics {and} Application Section, Bhabha
Atomic Research Centre, Mumbai, India
Correspondence:
[*]
Corresponding author: M.S. Ansari, Laser Electronics Support
Division, Raja Ramanna Centre for Advanced Technology, Indore 452013, India.
Tel.: +91 731 248 8466; Fax: +91 731 284 8430; E-mail: msa@rrcat.gov.in
Abstract: This paper presents mathematical analysis and measurement results of
electromagnetic couplings through a pair of intentional apertures in a metallic
enclosure and its effect on the electromagnetic shielding effectiveness. The
enclosure houses an electro-optical device (Pockles cell) and its high voltage
drive circuitry. Two different aperture shapes i.e. rectangular and circular of
equal areas are compared over frequency range of 200 MHz to 2 GHz. Pockels
cells are commonly used in applications involving fast switching of
polarization to block or transmit laser light. Pockels cell assemblies are
housed in metallic enclosures to reduce noise emissions from high voltage
pulser circuits driving the cell and to minimize the field couplings from
external sources which may result into spurious switching of the cell. However,
apertures are required in the enclosure to enable the laser beam to be incident
on the Pockels cell and for onward transmission of the modulated beam. The
apertures result into reduced shielding effectiveness of the metallic enclosure
and increase in noise couplings. There is a need to understand the effect of
apertures and to properly select their shapes and sizes such that the
electromagnetic noise couplings are kept to a minimum acceptable level. Apart
from the functional requirements of a reliable and noise free system operation,
this issue is also important to meet the growing and stringent demands of
electromagnetic compatibility. The analysis and measurements presented in this
work pertain to the noise couplings from an external source into the enclosure
through two differently shaped apertures i.e. rectangular and circular. For the
comparison purpose, the planar areas of the apertures for the two cases are
kept equal. The analysis and measurement techniques described in this work will
be of interest to designers of electrical and electro-optical components for
laser systems.
