Frequency comb
The frequency comb generator is a measurement device for high-precision frequency measurement; indirectly be possible also highly accurate distance measurements. This instrument produces a light beam, the frequency comb, which allows the oscillation frequency of another light beam by five orders of magnitude more accurate than determine the methods known to date.
With a frequency comb, the frequency of electromagnetic radiation can be measured very precisely ( among others light). The device was invented in 1998 in the laboratory of Theodor W. Hänsch at the Max Planck Institute for Quantum Optics, in 2005 received the Nobel Prize for Physics for this.
The researchers had the problem of measuring a frequency of nearly 1015 Hz, which was previously impossible for the common electronics. So you can currently measure frequencies up to about 1011 Hz. The frequency comb operates according to the analogy of an optical transmission: The frequency to be measured is in a lower frequency translated, such as in radio waves. The centerpiece is a laser which emits light waves of very precisely known frequency provides that interfere with the light beam to be measured. It forms an interference pattern with a frequency in the radio band (called a beat ), from which can then infer the unknown frequency. A frequency comb not only uses a single frequency, but with a plurality of sharp lines in the visible region, the " teeth of a comb ," hence the name.
Construction
Is composed of the frequency comb generator of a femtosecond laser, the carrier - envelope phase is measured using a non-linear interferometer (f- 2f interferometer frequency doubling ) and kept constant.
The relatively broad optical spectrum of this laser consists of several very sharp lines together in precisely constant frequency spacing. With the f - 2f interferometer then both the distance between these " frequency pins " from each other, and the absolute position of the entire comb is measured. These two measures are easier to measure, because they are in the radio frequency range, and can be determined very accurately by comparison with an atomic clock. Thus, the absolute frequency of each frequency needle in the spectrum of this laser is known exactly now. By measuring a beat frequency difference between a frequency - calibrated in this way, the needle and a not so accurate known frequency of another beam can now be determined.
It is also significant the small size of the device; it is no larger than a shoe box. Previous experiments for precise frequency measurement (the " frequency range " ) took several rooms.
Applications
The main application areas are:
- Several orders of magnitude higher data transmission rates in optical fibers with less interference to adjacent channels, and improved security against eavesdropping, so that eg more telephone calls can be transmitted simultaneously with an overseas Light Cable
- Cheaper and probably several orders of magnitude more accurate replacement for mobile atomic clocks, among other things, for satellite navigation are important
- Highly sensitive chemical detectors
- Expanding the limits of the "designer chemistry" in the field of ultracold chemical reactions.
- Improvement of distance measurement systems based on the lidar technology by several orders of magnitude. With this device, for example, the very small Doppler shifts in the spectrum can be around each rotating star can be measured so precisely that even can be detected when planets around distant suns circle; because if there is a small planet around a heavy sun revolves, both rotate around a common center of gravity, which is not far from the Sun center. This results in a slight swing of the main star, which causes a small Doppler shift. With the frequency comb can be the extent of the Doppler shift measured, from which the planet's orbit can be calculated.