Amplified ultrafast Ti:sapphire laser systems with typical performance of 100 fs and 1 mJ at 1 kHz are moving into mainstream research and industrial applications.
Danny Anderson, Dr. Jurgen Kolenda, David Heck, Dr. Qiang Fu and Mark Ortiz
Two basic types of amplified ultrafast Ti:sapphire laser systems
are commercially available: individual component systems, such as the Titan or Odin
from?Quantronix Corp., where the mode-locked oscillator, pump laser and amplifier
are separate units, and all-in-one systems, such as the company’s Integra.
Which system a user chooses depends on the application.
Component systems offer the user a great deal
of flexibility in selecting output pulse energies and wavelength. Amplifiers generally
offer a tuning range of 750 to 850 nm. Typically these component systems take up
about half of a 4 x 8-ft optical table. The all-in-one units offer turnkey operation,
the convenience of reduced size (2 x 4 ft, or 60 x 120 cm), and increased output
energy stability resulting from better control of the environment within the single
laser enclosure.
Amplified Ti:sapphire systems also
offer extremely high peak powers and pulse energies, short pulse widths and good
beam quality. With pulse energies as high as 5 mJ and peak powers at the terawatt
level, ultrafast amplifiers are becoming increasingly popular in materials processing
applications. The short pulses keep the heat-affected zones to a minimum, and a
repetition rate of up to 10 kHz yields extremely fast processing times. By using
multipass amplifiers, pulse widths as short as 25 fs and high spatial quality (M2
<1.4) are obtainable.
These systems are used primarily in
research laboratories for high-energy applications such as terahertz imaging, soft
x-ray generation and processing of difficult materials. They also are used to pump
optical parametric amplifiers in short-pulse tunable applications, such as pump-and-probe
spectroscopy and four-wave mixing. The ease of operation of all-in-one units has
brought amplified Ti:sapphire systems out of academic environments and into more
application-oriented laboratories.
The main industrial use of amplified
ultrafast systems has been in micromachining and materials defect removal, both
of which require high-energy, short-pulse systems with good beam quality. In micromachining,
the high repetition rates available from the amplifiers coupled with the high pulse
energies greatly reduce processing times. The excellent beam quality allows high-aspect-ratio
via hole drilling and submicron feature processing (Figure 1).
Figure 1. The scribing produced by an ultrafast laser on a sapphire
wafer has a kerf 10 μm wide and 50 μm deep.
The increased use of these amplified
laser systems in industrial applications is driven by a combination of the need
for low-heat-affected-zone processing and the availability of turnkey package systems
that combine the laser with sample handling, automation and imaging in a single
workstation. The Quantronix DRS 855 photomask defect repair system fixes defects
that are as small as 200 nm with an accuracy of better than 50 nm.
Research applications such as coherent
x-ray generation and laser ignition are pushing the need for energy levels in the
tens of millijoules and beyond. The desire to use high-energy, ultrashort pulses
in industrial, medical and biological applications will propel the development of
simpler, more robust systems that offer energies high enough to pump multiple optical
parametric amplifiers or to drive multiple processing stations. Currently, all-in-one
amplifiers can offer pulse energies as high as 3.5 mJ, which is enough to simultaneously
pump up to six optical parametric amplifiers.
This kind of flexibility allows researchers
to run multiple beam lines at wavelengths from as low as 190 nm to more than 18
μm concurrently. For the industrial user, high repetition rates of 10 kHz and
above increase material throughput and allow processing of larger areas. Markets
such as photolithography and the manufacture of thin-film transistors and wafers
can all benefit from reliable, high-energy femtosecond lasers.
Meet the authors
Dr. Qiang Fu is president of Quantronix Corp.
in East Setauket, N.Y., where David Heck is director of scientific sales and Danny
Anderson is a senior sales engineer.
Dr. Jurgen Kolenda is vice president
of sales for Quantronix/Continuum Div. of Excel Technology Europe GmbH in Darmstadt,?Germany.
Mark Ortiz is vice president of sales,
marketing and business development for Excel Technology, also in East Setauket.