A detailed explanation of mid-infrared fibers and their applications
Ultra-fast pulse tuning frequency conversion based on hollow core fibers
There are several types of hollow core fibers: band gap, negative curvature and Bragg cladding. Regardless of the type, the preparation process is complex. Many people would also question the application of hollow core fibers, considering them too heavy and immature. However, this technology, which conceals new physical phenomena, offers a rare environment for many experiments. Today we present tunable frequency conversion of ultrafast pulses based on optical fibers. Using a drawn hollow fiber filled with nitrogen, ultrafast 1 μm laser pulses can be tunably converted to longer wavelengths and shorter pulse times.
In this conceptual diagram, the ultrafast laser pulse (blue) on the left enters a stretched hollow-core fiber filled with nitrogen (red molecules) and, as it propagates, obtains a spectral broadening, with the output beam (orange) on the right. This nonlinear phenomenon is due to the Raman effect, which is linked to the rotation of gas molecules in the laser field.
Yb fiber lasers can produce ultrafast pulses with a central wavelength of about 1 μm, but in many applications (e.g., high harmonic generation, OCT optical coherence tomography in medicine), Ultrafast pulses with high energy and slightly longer wavelength are required. ). Conventional sources of wavelength-tunable ultrafast pulses, optical parametric amplifiers (OPAs), convert ultrafast 1 μm pulses to frequency and allow continuous tuning from 1,3 to 4,5 μm, although the range of 1,0-1,3 μm cannot be achieved without additional frequencies. Additionally, takeover bids are generally complex and expensive to construct.
