Ruhr University Bochum
Prof. Dr. Clara Saraceno
PULS – Photonics and Ultrafast Laser Science
Förderprojekt: HoLa – EXIST Forschungstransfer
Postfach: ID 17
Universitätstr. 150
44801 Bochum
Germany
High-Performance Ultrafast Lasers
RayVen offers industrial-grade ultrafast lasers that operate exclusively at 2.1 µm (short wavelength infrared range, SWIR). Designed with femtosecond and picosecond pulse durations, these lasers deliver exceptional stability in a compact design, low-noise performance, and high peak power.
RayVen-S provides 1 W of average power at a 50-70 MHz repetition rate, with 120 fs pulse durations across wavelengths from 2090 nm to 2120 nm.
RayVen-L is tailored for high-energy tasks, delivering 10 W of average power and up to 1 mJ of pulse energy with 800 fs pulse duration.
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Interfaces on backside
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Laser aperture
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Dust-tight industrial design
What is the current scope of applications for 2-micron ultrafast lasers:
Semiconductors
2.1 µm ultrafast lasers are suited for processing of low-bandgap materials. Such materials are, for example, various pure semiconductors, e.g. Silicon (Si, bandgap 1.1 eV) and Germanium (Ge, 0.66 eV), and many compound semiconductors, such as Gallium Arsenide (GaAs, 1.43 eV) or Indium Antimonide (InAs, 0.36 eV). The low photon energy associated with 2 µm wavelength (0.59 eV) allows the light (i.e. the photons) to penetrate and transmit such materials instead of being absorbed directly at the surface. This allows focusing of the laser beam at any position within the volume of the material and, due to the high intensity of the ultrashort pulses, to trigger nonlinear effects that result in localized material property changes.
The minimal scale of the modifications thereby is in the range of a few micrometer (5-10µm / 2-5x the wavelength), which is due to the numerical aperture of the focusing optic and the beam shape and beam quality.
Finally, the induced modifications are desired defects, which can be left in place to locally change the stress inside the material, i.e. for the fabrication of waveguiding structures, or can be ablated when they are at a surface or can be removed from within the material via etching of a such-written channel. This gives rise to various opportunities for device fabrication, ranging from photonic chips, to cooling structures or vertical, but not necessarily straight channels for the interconnection of stacked chips.
The ability to traverse the material may allow welding of semiconductors to one another or even to dissimilar materials by being able to focus into the material interface plane. This is path to glue-less assembled electronic and optoelectronic devices.
The example shown here displays a thin line (around 20 µm wide) that was scribed onto a fine ground silicon wafer using RayVen-L. The wafer could be broken along this line, leaving a fine cleaved edge.
Glasses
Most optical glasses, such as fused silica and borosilicate, are oxide-based and still transparent around 2 µm wavelength. This allows for the light of an ultrafast laser like RayVen-L to do machining on the surfaces and within the material, as shown in the example to the right. The low photon energy at 2.1 µm requires a multi-photon absorption to happen to bridge the bandgap of the materials. This results in a very precise 3-dimensional localization of the defect to be induced. Possible applications are the drilling of through vias, writing of waveguides, welding, and the generation of diffractive structures. Hollow structures can be fabricated by etching of the laser-modified material.
Polymers
Polymers are materials composed of very long chains of molecules. Examples are the widely used polycarbonate (PC), polyethylene (PE) or Polymethyl Methacrylate (PMMA), but also Polysiloxanes (silicones) or organics like cellulose. The intermolecular bonds in polymers cause strong absorption in the short-wave infrared associated with the vibrational modes of these bonds. Resultingly, the radiation of a RayVen laser can hardly penetrate polymers and is almost immediately absorbed at the exposed surface. This allows for micrometer-precise ablation depth for machining of structures (down to voxel sizes of about 10x10x1 µm). Such structures could be used to create the various channels and chambers of lab-on-chip devices for all sorts of chemical, biological or medical analyses.
The example shows a trench of about 15µm width written on a piece of PMMA using RayVen-L.
Supercontinuum generation
Optical frequency combs are transforming fields like attosecond science and spectroscopy. Achieving stable frequency combs hinges on precise carrier-envelope-offset frequency (fCEO) stabilization, which requires octave-spanning spectra. Traditional broadening methods face challenges with Tm- and Ho-based ultrafast lasers due to anomalous dispersion at their emission wavelength. Integrated waveguides are emerging as powerful tools for generating supercontinua at low pulse energies and with engineerable dispersion.
Octave Photonics and the group Photonic and Ultrafast Laser Science at Ruhr University Bochum generated an ultra-broad spectrum of light, spanning from 1.2 µm to 3.2 µm using RayVen-S. The supercontinuum generation was accomplished using Ta₂O₅ waveguides designed and manufactured by Octave Photonics. This technology paves the way for advances in mid-infrared lasers. Figure (a) displays the measurement scheme and figure (b) shows the output spectrum of the chip.
RayVen brings 2 micron to industrial and scientific users
2 µm lasers open new pathways in material processing. For example, silicon – a fundamental material in the electronics industry – becomes transparent around 2 µm, enabling processing through the material and inside of it. Contrary, in polymers, the absorption peaks at around 2 µm allowing for efficient surface processing. Additionally, 2 µm lasers exhibit strong absorption in water, enabling precise medical procedures such as urology treatments and soft tissue surgery with small penetration depth. Further, the eye safety is higher compared to 1 µm laser because it is less likely to damage the retina.
Beyond industrial applications, 2 µm femtosecond lasers hold potential for scientific research. They allow spectroscopy of various chemical species and water. Additionally, they serve as drivers for nonlinear frequency conversion to EUV and THz.
RayVen builds solid-state lasers, here is why:
Solid-state lasers excel in producing high peak powers, high energy and high beam quality, crucial for ultrafast science and precision material processing.