Wavelength shifts in tuning dye lasers

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It is shown that the output wavelength lambda(m) of a dye laser may be shifted with respect to lambda(0), the wavelength setting to which the dye laser is tuned by an intracavity wavelength-selective optical element such as a diffraction grating. The shift delta lambda = lambda(0) - lambda(m) is toward the wavelengths at which lasing would occur without the tuning element in the cavity. The magnitude of delta lambda is determined by the spectral width of the tuning element by the gain characteristics of the laser dye and by cavity design parameters. An analytic expression is presented for a dye laser oscillating at threshold gain and for a Gaussian wavelength distribution of the dispersive element. Some examples are discussed where wavelength shifts may be significant.