| As the greatest inventions of the 20th century,laser,semiconductor,atomic energy and computer,play an important role in the high technology era and become increasing significant in the national security,the industrial manufacture and the civil life.Crystal materials,such as synthetic crystals,a media of light,electricity,acoustic,heat,mechanic and other forms of energy,have been aroused wide attention in the world.Crystal growth has a long history in China and is developing rapidly at the present.Therefore,it is necessary to comprehensive evaluation of crystal material with great potential application prospects,and then the innovative exploration on crystal material should be persisted and enhanced to avoid the research gap in the related field.Mid-infrared(MIR)and far-infrared(FIR)lasers in the range of 3-12 ?m are essential for the applications,such as in national security,infrared countermeasures,infrared guidance,telecommunications,minimally invasive surgery,remote sensing,etc.Therefore,researchers are paying more and more attention to explore the technology of MIR and FIR lasers.As the core component of all-solid-state laser frequency conversion system,using nonlinear optical(NLO)crystals is one of the main method in the generation of MIR and FIR lasers.The relationship between structure and properties of the IR crystal materials is considered and designed comprehensively to obtain its excellent physical performance.The light Li+ ions can increase the frequencies of the crystal lattice vibrations and the Debye temperature.This enlarges the band gap of these compounds,and improves the laser induced damage thresholds(LIDT)and higher thermal conductivity.LiInSe2,as one of the I-III-VI2 semiconductors with orthorhombic structure,include a large nonlinear coefficient,a wide transparency range and high LIDT.This results contribute significantly to the practical applications of LiInSe2 in the MIR and FIR technology field.Due to the important role of infrared technology in the national defense science and technology,this kind of crystal material is imposed an embargo by the foreign countries at present.Therefore,the study of this high efficiency and high power MIR and FIR optical crystals is critical important.In this thesis,the growth of high quality LiInSe2 crystal was systematically studied.The characterization of basic physical properties,crystal defects,and OPA devices performance based on LiInSe2 were systematically studied.In addition,an ultrasensitive photodetector was based on high-quality LiInSe2 crystal was systemically designed and investigated.And this work may lay the foundation and ignite future research interest on chalcogenide crystals in photodetectors.The main research outline and conclusions of this thesis are as follows:I.An overview of several representative NLO crystals.In this paper,from the point of the compositions of NLO crystal materials,several kinds of phosphide crystals(ZnGeP2,CdSiP2)and chalcogenide crystals(CdSe,GaSe,LiInS2 series,and BaGa4S7 series)are summarized.Furthermore,the above-mentioned attractive properties of these materials such as in the unique capabilities,the crystal growth,and the output power in the MIR and FIR region are also reviewed.II.High quality polycrystalline synthesis of LiInSe2.The effect of temperature field,mixture ratio,heating rate,reaction temperature on the synthesis of polycrystalline LiInSe2 is systemically investigated.Initially,the preparation of polycrystalline LiInSe2 involves a conventional high temperature solid-state reaction technique from high purity Li,In and Se.Initially,a stepwise heating program is designed to avoid the quartz ampoule explosion and 360 g single-phase polycrystalline LiInSe2 can be obtained in one cycle.However,the inevitable problem of quartz ampoule explosion that makes the yield reduction.Then,we develop a novel method of autoclave to obtain polycrystalline LiInSe2 and the probability of success can be reach to nearly 100%.And the experiment cycle can be greatly reduced to 5 days.III.Crystal growth and process optimization of LiInSe2 single crystal.As the innovation of this paper,the experimental equipments for crystal growth have been designed and optimized.The conditions of growing LiInSe2 by spontaneous nucleation and oriented seed have been systematically explored.Bulk single crystal of LiInSe2 with dimensions of ?12 mm??16 mm??21 mm??26 mm and ?31 mm have been grown by the oriented seed.The high quality of LiInSe2 crystals was demonstrated by X-ray Laue back scattering,optical interferometry,and high resolution X-ray.All the above characterizations reveal that high-quality LiInSe2 crystals are obtained by the Bridgman growth.?.Physical properties and defects characterization of LiInSe2.The basic physical properties of LiInSe2 were studied systematically based on the high-quality LiInSe2 crystals.Single-crystal X-ray diffraction data of LiInSe2 was collected.The thermal and optical properties of LiInSe2 crystals were investigated in details.The transparence range of LiInSe2 crystals were determined to be 0.5-14.5 ?m.Refractive indices of the crystal were measured and the Sellmeier equations were obtained.LiInSe2 is optically negative biaxial crystal and its large refractive indices and birefringence,indicating that it possesses a moderate birefringence for phase-matching.For the first time,we studied the electro-elastic properties of LiInSe2 crystal at room temperature,indicating that LiInSe2 crystals may also have potential applications as piezoelectric device.Based on the coordinates of each atom and the corresponding bond length,the valence of Li+,In3+ and Se2-were calculated,respectively.The relationship between the piezoelectric properties and the dipole moments of LiInSe2 crystals were also analyzed.The annealing effects on infrared transmittance of LiInSe2 single crystal were studied in detailed.After annealing,the absorption coefficient of LiInSe2 can be decreased from 0.165 cm'1 to 0.093 cm-1 at 1064 nm.?.Optical parametric amplifier(OPA)laser output based on LiInSe2 crystal.A picosecond(ps)MIR OPA with LiInSe2 crystal was demonstrated for the first time.The MIR OPA was pumped by a 30 ps 1064 nm Nd:YAG laser.A maximum idler pulse energy of 433 ?J at 4 ?m has been obtained under a pump energy of 17 mJ,and the corresponding pulse duration was estimated to be?13 ps.An idler spectrum tuning from 3.6 to 4.8 ?m was investigated at fixed pump energy of 15 mJ.Furthermore,a 7-12 ?m widely tunable ps MIR OPA based on a LiInSe2 crystal was also illustrated.The idler operating at 7.5 ?m with the highest pulse energy of 170?J was obtained under a pump energy of 14 mJ.And the corresponding energy conversion efficiency is?1.21%,and the photon conversion efficiency is 8.6%.The output energies were measured to be?121 ?J at 7 ?m and?21 ?J at 12 ?m.?.Ultrasensitive photodetector based LiInSe2 single crystal.In this paper,an ultrasensitive metal-semiconductor-metal(MSM)structured photodetector based on high-quality LiInSe2 crystal was systemically investigated for the first time.Remarkably,the LiInSe2 based photodetectors exhibit an outstanding photosensitivity with a high on/off current ratio(6.80 × 104),fast photoresponse(trise=180 ?s and tdecay = 200 ?s),and high detectivity(2.16 × 1012 Jones).The high photosensitivity and fast photoresponse are attributed to the high-quality LiInSe2 crystal.Our results might open up the unique possibility of photodetectors based on LiInSe2 for practical applications. |
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