This application note gives a basic procedure for optimization of excitation and emission wavelengths of the SPECTRAmax GEMINI microplate spectrophotometer. If the two wavelengths are close together, the selection/optimization process is less straightforward, because of the need to minimize excitation light carryover. If the two wavelengths are far apart the choices are easy: the excitation and emission maxima are selected, along with an appropriate cutoff filter to remove residual excitation illumination and optimize sensitivity. For a particular fluorophore, the choice will depend on the location of its excitation and emission maxima and the separation between them (Stokes’ shift). Given the flexibility, the user naturally wishes to choose the best possible combination. The GEMINI contains both excitation and emission monochromators such that any combination of wavelengths between 250 and 850 nm is easily obtained. With the introduction of the SPECTRAmax GEMINI, it is no longer necessary to use bandpass filters or to settle for suboptimal wavelength compromises.
If the existing filters could not be used, it was necessary to purchase and install different ones. The best available filter was often 20, 30 or even 50 nm away from the optimal wavelength of the fluorophore. For a given application, the wavelengths of the filter pair did not necessarily correspond to the optimal excitation/emission wavelengths of the fluorophore. Until recently, all microplate spectrofluorometers were filter-based instruments equipped with a limited number of excitation/emission filter pairs. PROTEIN DETECTION, QUANTITATION, ANALYSIS.This is often referred to as the fundamental mode cut-off, or bend edge.COVID-19 RESPONSE - We are committed to supporting our scientific community during this pandemic. At wavelengths shorter than cut-off several optical modes may propagate - the fiber is multi-mode.Īs the cut-off wavelength is approached, progressively fewer modes may propagate until, at cut-off, only the fundamental mode may propagate - the fiber is then single-mode.Īt wavelengths longer than cut-off the guidance of the fundamental mode becomes progressively weaker, until eventually (usually at a wavelength several hundred nanometers above cut-off) the fiber ceases to guide - the fiber loses all optical function.The cut-off wavelength is the wavelength at which an optical fiber becomes single-mode.For example, if you are using a helium-neon laser, at 632.8nm, then you need HB600, while a 1550nm diode laser would call for HB1500. If you need Single Mode operation, you should choose the fiber type with the closest cut-off wavelength range below the operating wavelength of your optical source. HB450, SM600 etc.) typically represents the ‘nominal’ cut-off wavelength.
When referring to Fibercore products, the number in the fiber product code (i.e. 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. 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.