The National Institute of Standards and Technology (NIST) has developed a nominally quarter-wave linear retarder for wavelengths near 1.3 mum that is stable within +/-0.1 degrees retardance over a range of wavelength, input angle, temperature, and environmental variations. The device consists of two concatenated Fresnel rhombs made from a low stress-optic-coefficient glass that minimizes the residual birefringence from machining and packaging. Device machining, assembly, and antireflection coating tolerances are discussed, and the theoretical performance is compared with measurements. Humidity can modify retardance of the total-internal-reflection surfaces; we discuss packaging that mitigates this effect and provides an estimated 10-year lifetime for the device. Several measurement methods were intercompared to ensure that the device retardance can be measured with an uncertainty less than 0.1 degrees . Similar retarders will be certified by NIST and made available as Standard Reference Materials.
The National Institute of Standards and Technology (NIST) is developing a quarterwave linear retarder for operation at 1 .3 tim. It is expected to be stable to within 1 °o ver practical ranges of wavelength, temperature, and incidence angle. A spectral range of at least 10 nm is desired to accommodate solid-state and diode laser sources and typical wavelength variation. Normal incidence operation with an angular tolerance of°allows alignment by retroreflection of a collimated input beam. Operation over a temperature range of 25 10 °C encompasses most laboratory conditions, and practical rates of temperature change must also be allowed. STANDARD RETARDER PROGRESSThe theoretical retardance stability of birefringent waveplates subjected to changes in temperature, wavelength, and incidence angle was previously analyzed [1]. Retardance tolerances for a waveplate can be easily calculated for a given material. Changes in input angle (SO), wavelength (), or temperature (ST) that cause a 1 °c hange in retardance in a 90° quartz waveplate are shown in Table 1 . These values are also listed for a double Fresnel rhomb device which produces retardance through total internal reflection (TW). Though Fresnel retarders typically exhibit significantly worse performance than expected because of stress-induced birefringence, our device uses a lead-doped flint glass (847238) with a low stress-optic coefficient [2] and suffers negligible birefringence despite fabrication, polishing, and packaging stresses. Table 1 . Calculated variations for 0.1 °retardance stability Waveplate Thickness zO (deg) z (nm) iT (°C) quartzt (m=2) 340 im 1.4 0.15 0.73 quartz compound zero-order 642 im 1 .0 1 .3 6.5 quartz true zero-order (m=0) 38 im 4.1 1.3 6.5 low stress-optic glass 15.6 cm 3.7 +220 I -160 -double rhomb tFor crystal quartz, n0 = 1.5309, n = 1.5395, and Ln = 0.0086 at ) = 1.307 im [3J. Dependence of retardance on temperature and wavelength is calculated from [1]. "m" refers to the order number of individual waveplates.We use three methods to measure retardance. Two methods are modified versions of standard polarimetric measurements and use rotating polarizers. These are complemented by an interferometric method that is less sensitive to source power variation. Comparing measurements of retardance in a stable rhomb shows excellent agreement among the three methods, and accuracy within has been demonstrated through intercomparison of independent measurements of stable rhombs. 208 ISPIE Vol. 2873 0-8194-2271-1/96/$6.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/15/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
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