This is often referred to as the fundamental mode cut-off, or bend edge.
When referring to Fibercore products, the number in the fiber product code (i.e. HPLC Solvents, Acetonitrile and Methanol, Key Differences and Properties MeOH, ACN, Pressure, Solubility, Viscosity, Absorbance, UV cut off. UV-Visible Spectroscopy Multiple Choice Questions and Answers for competitive exams. At wavelengths just below the cut-off, a few modes may be guided, whilst multi-mode fiber operates far below the second order cut-off point. The tables below show the UV cut-off of the most commonly used buffers, solvents and additives in HPLC. Only mobile phases with a UV cut-off below the detection wavelength will not compromise the signal sensitivity.
Cut-off wavelength is important because, in most cases, it determines your choice of fiber type. Which mobile phases work with my detection wavelength Certain buffers or organic solvents interfere with UV detection. When referring to Fibercore products, the number in the fiber product code (i.e. All liquids have an ultraviolet cutoff, meaning that at and below some wavelength in the ultraviolet they absorb so much of the UV light that they cannot be used as solvents for spectroscopic purposes in this range. Cut-off wavelength is important because, in most cases, it determines your choice of fiber type. The second order mode cut-off wavelength (commonly shortened to cut-off) refers to the wavelength above which the fiber is single-mode only at wavelengths above the cut-off will the fiber guide be single-mode. Solvents for spectroscopic use need to be transparent in the wavelength or wavenumber ranges where the desired spectral information is to be obtained.