Ultrafast Laser Systems Find Work Outside the Lab

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.