Glued-laminated Prism Transmission Performance

When it comes to polarization prisms made in natural birefringence calcite,crystal,their veneer forms contain air-gap style and optical cement style;a case in point of the former is Glan-Taylor prism,and its advantageous virtue is that it has high anti-optical damage threshold, but the field angle is small,generally no more than 6°;prism that can represent the latter is frequently used Glan-Thompson prism,its most dramatic virtues are higher transmission and larger field angle.The two styles can be called as Glan prism,and optical cement style prisms and air-gap style are be designed similarly.Optical cement style prism is a better design for optical application and is the most universal style in application now.Although Glan types require considerably more calcite than Nicol types of comparable size,they are optically superior in several ways.①Since the optic axis is perpendicular to the prism axis,the index of the extraordinary ray differs by a maximum amount from that of the ordinary ray.Thus,a wider field angle or a smaller L/A ratio is possible than with Nicol types.②The light is nearly uniformly polarized over the field;it is not for Nicol types.③There is effectively no lateral displacement in the apparent position of an axial objectviewed through a(perfectly constructed) Glan-type prism.Nicol types give a lateral displacement.④Since off-axis wander results in images which have astigmatism when the prism is placed in a converging beam,Glan types have slightly better imaging qualities than Nicla types.For the fabrication of polarization devices,optical cement is necessary.There are many parameters to describe the performance of optical cement.Among them,wavelength range, transmission,operating temperature,shearing strength,linear expansibility,refractive index and dispersion are often used.At present,Canada balsam(also called neutral resin adhensive)and fir gums are often used in making up Glan-Thompson prisms.Generally,the length-width ratio (L/A)of the prism is 3,field angle ranges from 11°to 13°,and transmission can get 90%,in these aspects,the refractive index of optical cement(n₂)plays the most significant role.Now that n₂ affect prisms properties,we should find out the rule.To the best of our knowledge, there are no reports on optical cement used in polarization prisms.Here,we take Glan-Thompson prism as an example to analyze how the index affects its structure angle,field angle and transmittance.The principle can also be used for different other types of prism.Since there is no satisfactory cement which can be used at 214nm,where calcite beginsto absorb stronglyt for applications involving an extended wavelength range from the ultraviolet to the,Glan-Thompson-type prisms used in this range must be air-spaced.Air-spaced prisms are also convenien near infrared.Analyze the influence of the cement used in Glan-Thompson prisms,we can get the following conclusion,the basic parameters of the prisms can also be greatly influenced by the air-space.The prime reason is the multiple-beam interferometer caused by the thickness of the air space.Thus it can bring influence to the transmission of the prisms. The cement used in Glan-type prisms can be seen as a layer of thin film.And we can analyse the influence of the cement on the transmission of Glan-Thompson prisms using the knowledge of optical thin film.The influence of thickness and the refractive index of the cement on the reflectance at the cementing surface has been studied in detail.And the rule is found out.The result shows that the thickness and the refractive index of the cementing layer does have great influence on the transmission of the prisms,and the influence of the former takes effect periodically,and the value of refractive index of cement takes effect to oscillation amplitude of the transmission.The result is very helpful for optimizing the transmitting performance of Glan-type prisms.In this paper,the influences of the cementing layer to the transmission parameters of Glan-type prisms are emphasized.Furthermore,according to the theory of prism designation and the basis knowledge of polarized optics,the influences caused by several factors such as the refractive index and thickness of the cementing layer to the transmission performance are discussed in detail.All details are as following.In Charter One,the basic start point and essence of this thesis are given.In chapter two,Glan-Thompson prisms are taken as examples.The influences of the refractive index to the field angle,structure angle,and the transmission of the prisms are mainly analyzed.Furthermore,the effects of the thickness of the cementing layer to the transmission performance are also analyzed.In chapter three,the Wollaston prisms are taken as examples,the influences of the refractive index and the thickness of the cementing layer to both the splitting ratio and the transmission are analyzed in detail.In chapter four,air-spaced-type prisms are analyzed independently.The influences of multiple-beam interferometer to the transmission performance of the air-spaced prisms are analyzed in theory,and verified in experiments.The originality innovation points in this thesis are as follows:First,according to the theoretical analysis,we know how the refractive index of the optical cement affects the transmission of the polarization prisms.The conclusion offer the theoretical laws for choosing the suitable optical cement and is greatly helpful to the optimization of the polarization prisms.Second,we can analyse the influence of the cement on the transmission of Glan-Thompson prisms using the knowledge of optical thin film.The result shows that the thickness and the refractive index of the cementing layer does have great influence on the transmission of the prisms.The influence of the former takes effect periodically,and the latter takes effects to the oscillation amplitude of the transmission:In general,the requirements of optimizing Glan-type prisms are realized.Higher expected transmission is realized.The influences of multiple-beam interferometer caused by the thickness of the cementing layer to the transmission of the prisms are also analyzed theoretically.Ideal results are also obtained.However,how to control the thickness of cementing layer is still a problem.