Femtosecond laser
Femtosecond lasers are lasers that emit light pulses with a duration in the femtosecond range. The laser light, which propagates at the speed of light, only covers a distance of 0.3 µm within a femtosecond , this distance corresponds to about a hundredth the diameter of a human hair.
Femtosecond laser compress the energy over mode coupling in an extremely short time period , shorter still than Q-switched picosecond lasers , and have therefore compared to continuous wave lasers, much higher peak powers (over the megawatt range addition). These short pulse durations can only be achieved via non-linear effects , mostly via the Kerr effect .
One of the most powerful (femtosecond) lasers in the world, the Hercules from the Center for Ultrafast Optical Science (CUOS) at the University of Michigan , has a light output of 300 terawatts . With a total energy of 40 joules, the Berkeley Lab Laser Accelerator (BELLA) achieves a power of one petawatt within 40 femtoseconds, once per second .
Laser types
The Kerr lens mode-locked titanium-sapphire laser , which works with its wide gain region of approx. 200 nm at a central wavelength of approx. 800 nm and is very insensitive to thermal stress and the formation of a thermal lens, is widespread.
Applications
Femtosecond lasers are a basic element for large areas of photonics and non-linear optics . The access to the electromagnetic phase has made it possible to achieve even shorter light pulses in the X-ray range with pulse durations of a few attoseconds . Based on this technology, attosecond lasers and so-called “tabletop” X-ray lasers are developed. The use of both pulse types in a pump-probe experiment allows the observation of ultrafast electronic changes within excited atoms .
Further applications are in measurement technology . Due to the short pulse durations, correspondingly short events can be examined, which are relevant in photochemistry , see also ultra-short-term spectroscopy . The broad, low-noise spectrum with extremely high stability is also used for metrology , i.e. high-precision time measurement using the frequency comb divided by the modes , as well as for optical imaging and measurement methods such as multiphoton microscopy and optical coherence tomography .
In medicine , the femtosecond laser is used u. a. in dentistry , ophthalmology (especially in femtosecond lenticle extraction as a means of refractive surgery and in femtosecond laser cataract surgery as a means of cataract surgery ) or cancer therapy .
The advantages are here:
- high peak intensities
- low heat transfer to the substrate
- Broadband spectrum
Other possible uses of femtosecond lasers:
- the control or research of chemical reactions, for example the disintegration of certain molecules in the manufacture of drugs
- optical scanning methods for surfaces, for example
- the exact and residue-free removal of the smallest amounts of material without significant heat transfer (principle of the precision scalpel). The femtosecond laser converts the material directly into plasma , which hardly interacts thermally with the carrier material.
See also
Web links
Individual evidence
- ^ Berkeley Laser Fires Pulses Hundreds of Times More Powerful Than All the World's Electric Plants Combined Scientific American Blog Network
- ↑ Burkhard Dick, Ronald D. Gerste, Tim Schultz: Femtosecond Laser in Ophthalmology. Thieme, New York 2018, ISBN 9781626232365 .