The lateral position of the output beam is hardly affected it is only that ordinary and extraordinary components have slightly different propagation directions within the plate, and the direction of the extraordinary component changes somewhat by the rotation since it depends on the angle between k vector and optical axis. By adding a linear polarizer, which transmits only light with p polarization, one would obtain the blue curve.īy rotating the plate around an axis which is perpendicular to the plate surface, one can shift the transmission curve.Īs the angle of incidence is not changed, the low-loss condition for p-polarized light at Brewster's angle is not lost by the rotation. The plate is oriented at Brewster's angle, and its optical axis is rotated by 40° against the plane of incidence, where the optimum transmission contrast is achieved. Transmission spectrum of a single-plate birefringent tuner, made of a 2 mm thick α-quartz plate. Note also that there are simplified equations delivering only approximate results, and the limits of validity are often not obvious. Unfortunately, the scientific literature contains various errors in the corresponding equations. (Sometimes, one uses plates where the optical axis is not parallel to the plate surface, but has some angle against it.)įurther, one needs to apply the phase shifts experienced by the ordinary and extraordinary wave their difference is what essentially causes the wavelength dependence of the transmission.įinally, the amplitudes for s and p polarization just before the output surface need to be calculated, and after application of the Fresnel factors, one finally obtains the output amplitudes for s and p polarization. Then, one needs to calculate the complex amplitudes for ordinary and extraordinary polarization, taking into account that the optical axis can be rotated with an arbitrary angle against the plane of incidence. The mathematical analysis of the transmission properties is not trivial.įirst, one needs to use Fresnel equations for the amplitude transmission factors for s and p polarization. How to calculate the transmission spectra? That effect, however, is usually hardly relevant unless the beam radius is rather small.
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The thicker the birefringent plate, the smaller is the free spectral range.Īs the ordinary and extraordinary components have slightly different propagation directions within the plate (there is double refraction!), the corresponding contributions to the output beam do not perfectly overlap. The induced losses vary approximately sinusoidally with the wavelength. The birefringence leads to wavelength-dependent polarization changes and thus transmission losses, arising from the Fresnel reflection of s-polarized light at the surfaces or at an additional polarizer. Usually, it is inserted with an angle of incidence near Brewster's angle in order to minimize reflection losses for p polarization. of crystalline quartz), through which the intracavity laser beam propagates. The simplest kind of birefringent tuner has a single birefringent plate (e.g. By rotating the plate around the dashed axis, the transmission wavelengths can be tuned. Setup of a single-plate birefringent tuner. They make it possible to tune the output wavelength over hundreds of nanometers while introducing only small losses into the laser resonator. The wavelength of minimum loss can be shifted by modifying the tilt angle of the birefringent filter.Ī mount with a micrometer screw allows for precise adjustments.īirefringent tuners are often used in lasers with broadband gain media, for example in vibronic lasers such as titanium–sapphire lasers, in dye lasers, and sometimes in optical parametric oscillators. There are different tuner designs (see below), all exploiting the birefringence of some optically anisotropic crystalline plates.Ī laser containing such a filter will typically operate at a wavelength near a point with minimum transmission loss, if the filter curve is sufficiently sharp. How to cite the article suggest additional literatureĪ birefringent tuner is an optical filter device which is often used in a laser resonator for tuning of the output wavelength and/or for narrowing the optical bandwidth ( linewidth). German: doppelbrechende Wellenlängen-Einsteller More general term: wavelength tuning elements Using our ad package, you can display your logo and further below your product description.Īsk RP Photonics for advice on various methods for wavelength tuning of lasers.ĭefinition: devices for wavelength tuning of lasers, based on birefringence and polarization rotation