Dye lasers are tuned by using an adjustable optical cavity to select a specific wavelength from the inherently broadband output of the organic dye.
This selection process relies on components within the optical cavity that are adjustable, allowing specific wavelengths to be favored for lasing. The primary methods involve:
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Rotatable Grating or Prism: These elements act as dispersive components. By rotating the grating or prism, the angle of incidence of the light changes, causing different wavelengths to be reflected or refracted at different angles. This allows only a narrow band of wavelengths, determined by the grating/prism's orientation, to be fed back into the gain medium (the dye) and amplified.
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Movable Wedge of Refractive Material (e.g., Lyot Filter): A Lyot filter is composed of birefringent materials. By moving the wedge, the effective path length and therefore the phase retardation between orthogonal polarizations of light passing through the filter is changed. This allows the transmission of the filter to be tuned to a specific wavelength. This wavelength is then preferentially amplified in the laser cavity.
In essence, these methods use adjustable optical elements to create a wavelength-dependent loss or gain within the laser cavity. By adjusting these elements, the wavelength at which the loss is minimized (or the gain is maximized) is changed, thus tuning the laser. The tuning range is limited by the gain bandwidth of the particular dye being used.
