The Study On The Growth And Properties Of Infrared Nonlinear Optical Crystal CdSe

Cadmium selenide(CdSe)is a kind of ?-? compound semiconductor materials with excellent optical and electrical properties.Specially in the field of infrared nonlinear optical crystal materials research,CdSe has unique advantages such as wide light transmission band(0.75?25?m),low optical absorption(<0.01cm-1,1 to 10 ?m),high laser damage threshold,suitable for birefringence,smaller dispersion angle and wide phase matching band.At the same time,CdSe crystal has good chemical stability and machinability.These properties make it one of leading candidates for use as nonlinear optics devices,to achieve current urgent need 8-15 ?m infrared source that widely used in military and civil fields with 2.09 ?m Ho:YAG,2.797 ?m Cr,Er:YSGG lasers as pumping source.However,wide application of CdSe crystals has been limited for years probably because of the lack of high-quality large single crystals.At present,the following two factors may affect the crystal quality and still need further study.Firstly,the melting point of CdSe is high(1264?),so the container-quartz crucible is very easy to break at this temperature,and the traditional synthesis methods that have shortcomings of low synthesis purity,efficiency et.al are not suitable for this crystal.Secondly,CdSe contains toxic and volatile components at the melting point,also with high equilibrium partial pressures of Cd and Se along the liquids,which can induce inhomogeneities in composition,resulting in the degradation of crystal quality.Here in this thesis,the above mentioned problems have been studied and improved.Firstly,for the CdSe polycrystalline synthesis,the modified high temperature element synthesis method had been introduced.With the aid of numerical simulation,by lowering the pressure difference on the inner and outer crucible,the explosion and component deviation problems during synthesis procedure had been resolved roundly,and about 200g CdSe polycrystals could be obtained in one run.The X-ray powder diffraction(XRD),thermal analysis(TG/DTA),inductively coupled plasma mass spectroscopy(ICP)methods were used to characterize the synthetic materials,the test results showed the prepared materials were high purity and suitable for single crystals growth.Secondly,for the single crystal growth,the CdSe single crystal with 015 mm×35 mm size has been grown by the modified double-temperature zones horizontal vapor phase method with seed aided technique.The grown CdSe single-crystalline ingot is compact and integrated,and its surface is smooth.The obtained CdSe crystal samples were characterized by XRD,energy dispersive spectrometer(EDS),atomic force microscopy(AFM)and fourier transform infrared(FTIR)spectrometer.The XRD spectrum of CdSe is agreement with the standard diffraction peaks.The rocking curves of CdSe single crystal sample possess high intensity and good symmetry,and the full width at half maximum(FWHM)of the rocking curves is 0.5°.The stoichiometry ratio was tested by EDS to be Cd:Se=1:0.977,close to the ideal ratio of 1:1.The infrared transmission is beyond 65%in the region from 2.5 to 20 ?m,and the absorption coefficient a is less than 0.08 cm-1.The above results show that the as-grown CdSe crystal by this method has good quality.In addition,the nonlinear optical performances of CdSe crystal were calculated and discussed,and the results of simulation calculation will play a positive role in the follow-up laser frequency conversion experiments.Above all,CdSe polycrystalline synthesis and single crystal growth were studied systematically and made some progress in this thesis.The work of this study also provides useful reference in the study of III-V,II-VI compound crystals with high vapor pressures and high melting points.