"Transform your diodes into high-brightness lasers", is Unique Mode's optimistic slogan. The
company, a spin-off from the Fraunhofer Institute in Jena, Germany, has recently laid claim to a
brightness record: its high-power diode laser system offers more than 5.2 W at 975 nm from a 50 µm
fibre with a 0.15 numerical aperture.Thilo von Freyhold, head of research and development at
Unique Mode, said: "This is about 10 times as bright as diode laser systems that are usually available."
He envisages applications for Unique Mode's laser to include flexographic printing, where it can replace
solid-state and fibre lasers.
Torsana claims that its technology - a passive feedback system -
causes a diode laser to emit near-diffraction-limited output at powers of up to 5 W and that the beam
quality is close to that of a diode-pumped solid-state laser.
Unique Mode's system shapes the
emission of a wide-strip laser diode into a beam that is symmetrical in extension and divergence. When
the firm launched last year, it claimed that this was the first time that almost all of the power from a
diode laser had been concentrated into a highly collimated symmetrical beam that could be focused into
a small spot.
The company achieved this by using cylindrical lenses to transform the wide-line
emission of a laser diode into a virtual stack of line emitters with a much narrower width. This produces
a square emission with enhanced brightness.
According to a patent owned by Unique Mode
(WO127686, published in April), the set-up has a cylindrical-lens optical system per emitter, with each
system comprising one or more cylindrical lenses. These collimate each beam in the y direction.
Each beam is deflected at a different angle due to a rotation about the z axis of at least one of
the cylinder lenses or by providing a discontinuous deflection element.The diode laser system also contains a director-collimator optical device that collimates each
radiation beam in the x direction and deflects beams at several different deflection angles. This
means that the main beams of radiation coincide in the x direction at a defined distance from the
emitter and run in parallel in the y direction.Torsana owns a patent (WO9856087, published in
December 1998) for a "laser system using phase-conjugated feedback". It covers a set-up for the
"emission of a highly coherent, possible singlemode, output light beam" and is based on the formation of
an external cavity between the laser and, for example, a phase conjugator emitting a second light beam
in response to the first incident beam.
The patent states that: "A frequency selective element, such
as an etalon, is positioned in the external cavity. The feedback from the external cavity forces the first
laser to emit a stable and significantly improved spatially and temporally coherent high-power output
beam." The patent also says that a frequency-doubler crystal can be positioned in the external cavity, for
frequency doubling part of the light beam. The crystal can even be positioned inside the etalon, where
the laser beam has a high intensity and a high temporal coherence.Although Torsana's marketing
director, Anders Madsen admits that the company has not sold any systems yet, he told OLE:
"We are now placing products in the area between diode lasers and conventional lasers - an area almost
without solutions at present. In the past, the choice was either cheap diode lasers with poor beam
quality, or heavy and expensive conventional lasers with a high beam quality.
"Now that there is a
compromise available we expect dramatic growth in [our product] area in the years to come. Given that
our technology is completely wavelength independent, we expect to launch a range of StarBright
products at customer-defined wavelengths and powers."
The firm has two products: a 808 nm
laser, operating in continuous-wave mode at 300 mW; and a 980 nm laser, operating in
continuous-wave mode at 200 mW.
Madsen says that, compared with Unique Mode's products,
Torsana's products have a higher beam quality but lower power.
Freyhold of Unique Mode
confirms this. He said: "Torsana and Unique Mode are aiming at different sectors. We are pursuing
markets that demand higher power and a lower beam quality."
He claims that his company's
systems cost less than Torsana's because they use passive beamshaping technology with segmenting
optics. "There are no active components inside the module except the laser diode and the Peltier cooler,
and there is no need to modify the laser diode itself.
"We are able to combine our beamshaping
optics with any wide-stripe laser diode available on the market. Our optics consist of only a few parts,
mostly standard micro-optical components, and our mechanical concept is ideally suited to the mass
production of the modules."It seems that whatever the fine details of
the two firms' products, they have both discovered the same gap in the market at the same time. Detlev
Wolff, sales and marketing manager at Jenoptik Laserdiode in Germany, told OLE: "Most laser
diodes fall into one of two categories: low power with high beam quality; and high-power with low
beam quality. There is a gap in the market between one-emitter-strip elements, which have a maximum
output power of 2 W, and our bar-based diode lasers, which have an output power of 30 W. Unique
Mode and Torsana are jumping into this gap and we do not consider them as competition."Even
Unique Mode and Torsana, despite the similarities in their products, claim that they do not consider each
other as direct competition. Perhaps there is room in the gap for both start-up companies.
Torsanawww.torsanalaser.com
Unique Mode www.unique-mode.com
