A research team in the U.K. used twisted wave-fronts to transform the electric field and produce a different type of polarization.

A
new optical technique, capable of producing laser beams with unusual
modes of electric field, has been developed by scientists at the
University of Liverpool.

The
new technique could have a major impact on laser micro-machining, by
increasing process efficiency and quality through the use of different
modes of ‘polarization’ or electric fields. These are unusual states of
light and difficult to produce.

Many
lasers have linear polarization—where the electric field of the beam
is, for example, vertical everywhere. Radial and azimuthal
polarizations, however, have a directional change of electric field and
it is laser beams with these particular modes that have been produced by
scientists at Liverpool.

Broad range of uses

Laser
micro-machining with linear polarization is used in a wide range of
precision manufacturing industries, from the drilling of holes for fuel
injection nozzles, to the processing of silicon wafers and the precise
machining of medical stent devices.

The
Liverpool Laser Group, part of the School of Engineering, was able to
successfully demonstrate a flexible and cost-effective way of producing
radial and azimuthal polarization modes using a Hamamatsu Spatial Light
Modulator. This device or ‘magic mirror’ can rotate the polarization at
any point in the laser beam to any desired direction.

Olivier
Allegre, part of the team based at the Lairdside Laser Engineering
Centre led by Professor Ken Watkins, used a 100 femtosecond-pulse laser
source, together with a spatial light modulator and a wave-plate, to
demonstrate laser micro-machining with these new modes of polarization
which alter the interaction of the laser with any material.

Significant gains in processing speed and efficiency

Olivier
explained: “A 100 femtosec (fs) laser pulse lasts only
1/10,000,000,000,000 of a second—a remarkably short timescale—but this
is produced on a daily basis at the Laser Centre in Birkenhead. The
ratio of 100fs to 1 second is the same as 1second is to 300,000 years.”

He
added: “This technology and these new modes of polarization enabled us
to achieve significant gains in processing speed and quality when
micro-machining stainless steel plates. A radially polarized beam
increased the machining speed, due to the higher absorption of radial
polarization which increases the coupling of the laser energy during
machining.

“We
will now study how this new technique could improve the processing of
various materials, such as semiconductors and dielectrics. The technique
is also significant for improving image detail in microscopy, and could
benefit fluorescence-based imaging of biological samples.”

Source: University of Liverpool