FemtoFiber Technology for mid-IR Generation
- Vibrational mid-IR spectroscopy
- CEO-free frequency comb
- High harmonic generation
- Difference frequency generation (DFG)
- DFG generating 3 - 5 µm
- DFG generating 5 - 12 µm
The spectral region between optics and electronics lying in the mid-Infrared is difficult to access. Nevertheless it is of great spectroscopic interest because it hosts the majority of molecular finger prints: The important vibrational modes with energies 800 cm-1 – 3400 cm-1 are mapped to the excitation wavelengths of 3 µm – 12 µm. Typically, optical parametric oscillator (OPO) or amplifier (OPA) laser systems are used for generation of tunable, infrared laser light. However, common commercial systems don’t reach such long wavelengths of 3 µm or beyond.
Another method is based on difference frequency generation (DFG) employing ultra-broadband Ti:Sa lasers with more than 200 nm bandwidth. The major draw back here is the very low generated power because of mixing frequency pairs which lie at the outermost edge of the spectrum.
In contrast, TOPTICA’s ultrafast fiber lasers generate powerful mid-IR radiation tunable between 3 µm – 12 µm. This approach is based on DFG of two optically synchronized laser pulses at tunable wavelengths of 1 – 2 µm. Here, the powerful fundamental output at 1560 nm of an Erbium doped ultrafast fiber laser is mixed with the long or short wavelength part of a supercontinuum which is efficiently generated in a highly non-linear fiber. The non-linear crystals for DFG are periodically poled Lithium niobate (ppLN) or Cadmium selenide.
A welcomed side effect of the DFG approach is the elimination of the carrier envelope offset (CEO) of the mode-locked laser: The CEO-free mid-IR laser pulses are therefore applied to attosecond spectroscopy where the extreme UV pulses consist of only a few optical cycles. Both, carrier and envelope of the pulses, must be considered here. The conversion of mid-IR radiation to extreme UV is accomplished by high harmonic generation. First, the mid-IR pulses are amplified by several orders of magnitude with optical parametric chirped amplification (OPCPA). Then, the intense laser fields are launched into an atomic beam or a gas-filled hollow core fibre to generate extreme UV attosecond laser pulses via high harmonics.
- Brochures: Ultrafast Fiber Lasers
- Publications: Attoscience goes OPCPA, Hellerer, Optik & Photonik, 2012
- Publications: Mid-infrared difference-frequency generation of ultrashort pulses tunable between 3.2 and 4.8 µm from a compact fiber source
- Publications: Mid-infrared optical combs from a compact amplified Er-doped fiber oscillator
- Publications: Design and simulation of few-cycle optical parametric chirped pulse amplification at mid-IR wavelengths