Wide spectral range multiple orders and half-wave achromatic phase retarders fabricated from two lithium tantalite single crystal plates

Abstract

Abstract In a broad spectral range (300–2500 nm), we report the use of channeled spectra formed from the interference of polarized white light to extract the dispersion of the phase birefringence Δ n p ( λ ) of the x - and y -cuts of lithium tantalite (LiTaO 3 :LT) plates. A new method named as wavenumber difference method is used to extract the spectral behavior of the phase birefringence of the x- and y - cuts of LT plates. The correctness of the obtained birefringence data is confirmed by using Jones vector method through recalculating the plates thicknesses. The spectral variation of the phase birefringence Δ n p ( λ ) of the x- and y -cuts of LT plates is fitted to Cauchy dispersion function with relative error for both x- and y-cuts of order 2.4×10 −4 . The group birefringence dispersion Δ n g ( λ ) of the x- and y -cuts of LT plates is also calculated and fitted to Ghosh dispersion function with relative error for both x- and y -cuts of order 2.83×10 −4 . Furthermore, the phase retardation introduced by the x- and y -cuts of LT plates is also calculated. It is found that the amount of phase retardation confirms that the x- and y -cuts of LT plates can act as a multiple order half- and quarter-wave plates working at many different wavelengths through the spectral range 300–2500 nm. For the x- and y -cuts of LT plates, a large difference between group and phase birefringence is observed at a short wavelength ( λ= 300 nm); while such difference progressively diminished at longer wavelength ( λ= 2000 nm). In the near infrared region (NIR) region (700–2500 nm), a broad spectral full width at half maximum (FWHM) is observed for either x- or y -cut of LT plate which can act as if it is working as a zero order wave plate. Finally, an achromatic half-wave plate working at 598 nm and covering a wide spectral range (300–900 nm) is demonstrated experimentally by combining both x- and y -cuts of LT plates.