Growth And Characterization Of Several Disordered Crystals

As one of the greatest inventions of the twentieth century,Laser has been hailed as"the fastest knife","the most accurate ruler" and "the brightest light" Correspondingly,laser crystals,which are the core of the laser components,can be considered as "the blade of the fastest knife","the scale of the most accurate ruler",and "the source of the brightest light".Among the various laser crystals,disordered crystals,which possess both the disorder of glass and the order of crystal,have gradually demonstrated their superiorities in the field of laser due to their excellent spectral performance.In this paper,several disorderd crystals with specific applications including infrared laser,visible laser,ultrafast laser and magneto-optical function have been grown and investigated to meet the most urgent needs in the laser field.Three series of disorderd crystals with two kinds of crystal structures have been selected as the study objects.They are the CaGdAlO4(CGA)crystals with K2NiF4 stucture and the YSGG and TSAG crystals with garnet structure.The specific research contents are as follows:The origin of coloration and the physical properties of CGA crystals and their potential in visible laser applications.CGA single crystals have been grown in different oxygen concentration atmospheres by the Czochralski method.Crystals grown under an oxygen-containing atmosphere presented an inconsistent brown coloration.The origin of coloration was studied by density functional theory,and the simulated results show the oxygen defects and the absorption matched well with the experimental results.The brown coloration of CGA is due to the interstitial oxygen atoms.The fundamental properties of CGA crystals with different colors,including the crystal density,hardness,thermal and optical properties,were systematically investigated and compared when taking into account the effect of color center inside.The colorless CGA was grown under an inert gas atmosphere and exhibits a wide transparency range of 227-7140 nm.The maximum phonon energy was determined to be as low as 618 cm-1.The colorless CGA host crystal with a disordered structure,good thermal conductivity,low maximum phonon energy and wide transparency is promising for ultrafast ultraviolet and visible laser applications.Modified growth,properties promotion and spectra characterization of Pr:CGA crystals with great prospects for visible laserPowerful solid-state lasers with direct emission in the visible region,have attracted extensive attentions in the applications of data storage,medicine,spectroscopy,fluorescence microscopy,and display technology.But it is still in its infancy now.Potential gain medium was consider to be one of the most crucial factors affecting the development of visible laser.CGA crystal is an attractive host for visible laser.It possesses low phonon energy(as low as 618 cm-1),good thermal conductivity,good machinability,and fairly wide transparency ranging.In addition,the disordered structure of CGA crystal also provides great possibility in the output of mode-locked visible laser in the future.In this part,Pr:CaGdAlO4(Pr:CGA)crystals have been grown and investigated for the first time.A Na+ flux was utilized to improve the crystal quality in the Czochralski method.The modified Pr:CGA crystals have showed significantly improvement in crystallinity,optical homogeneity and thermal conductivity.The spectra properties of Pr:CGA were characterized in detail.All the properties prove that Pr:CGA crystal possesses great prospects in the applications of visible laser.Crystal growth,spectral broadening and ultrfast laser performance of Yb:CLGA disordered crystalYb:CaLuxGd1-xAlO4(Yb:CLGA)crystals have been grown and studied for the first time.A more disordered structure than that of the Yb:CGA crystal was designed by introducing Lu3+ ions into the crystal.The absorption spectra at 9.6 K provided clear evidence for the disordered structure of the Yb:CLGA crystal.Moreover,further spectral broadening was achieved compared to that of the Yb:CGA crystal.The crystal quality and spectroscopic properties of the Yb:CLGA crystal with the highest degree of disorder were investigated in detail.A SESAM-based mode-locking laser was achieved on Yb:CLGA 1#crystal by self-starting,generating reliable pulses as short as 69.6 fs.At a central wavelength of 1054 nm,a maximum average output power of 232 mW was obtained with the highest peak power of 63.7 kW.The same crystal was employed in wavelength tunable operation,and 65.7 nm of tuning range between 1023.1 nm and 1088.8 nm was obtained with a resolution of sub-0.1 nm.Besides,a BP-based mode-locked laser with the shortest pulse duration and the highest output power has been demonstrated by using the Yb:CLGA 1#crystal as the gain medium.Considering that the Yb:CLGA 2#crystal possesses better spectral properties,mainly having broader emission spectra than the Yb:CLGA 1#crystal,improved ultrafast laser oscillators with Yb:CLGA 2#,in terms of narrower pulse width and higher peak power,are expected in the futureCrystal growth and spectral properties of Nd:CGA and Nd:CLGA disordered crystalsNd:CGA and Nd:CLGA crystals have been successfully grown for the first time and the effect of Lu3+ on their spectral properties have been studied emphatically.The mesurment results show that the separation coefficient of Nd3+ ions in CGA and CLGA series crystals is 0.78,which is much larger than that in GGG(?0.4)and YAG(?0.2)crystals.The lager separation coefficient of Nd3+ ions is favorable for distribution uniformity of the crystals.Compared with the Nd:CGA crystal,the Nd:CLGA crystals possess lager specific heat and broader spectral properties.Especially,the FWHM of the main peak in the emission spectra of Nd:CLGA has been measured to be 22 nm,which is very favourable for the mode-locking in the generation of ultrafast laser.Therefore,Nd:CLGA is promising crystal in the Nd3+ ions actived ultrafast laser applications.Bulk growth and laser performance of Er:YSGG disordered crystals for IR laser applicationEr:YSGG crystals with maximum diameter of 35 mm and maximum length of 100 mm have been successfully grown by using an Ir crucible in diameter of 60 mm.High-resolution X-ray diffraction and Optical interferometry measurement have proved that the as-grown crystals are in high quality.The crystalline perfection of the as-grown crystal was evaluated with FWHM of the rocking curve being 32.61",and the optical homogeneity RMS being in the order of 10-6.The thermal conductivity of the 30 at.%Er:YSGG crystal at room temperature was 3.27 W·m-1·K-1.CW laser at 2978.7 nm has been achieved with a maximum output power of 745 mW and maximum slope efficiency of 31%.The slope efficiency is the highest level of the end pumped Er:YSGG laser.Crystal growth,magneto-optical properties and isolator performance of TSLAG disordered crystalTSLAG crystals have been successfully grown by Cz method.Its growth habit has been explored by using low cost Sc2O3 material.The value of Mohs hardness has been measured to be 7.6,indicating that the TSLAG crystal has good machining property.The optical and magneto-optical properties of the TSLAG crystal have been analyzed in detailed.As a magneto-optical crystal,the TSLAG crystal presents a high transmittance and a large Verdet constant.Its figure of merit has pointed out the superior characteristics of TSLAG crystal compared to TGG crystal.As a laser crystal,the TSLAG crystal has shown its potential in visible laser.There were an absorption peak at 486 nm and several emission peaks at 492 nm,543 nm,552 nm,592 nm,and 662 nm in the absorption and emission spectra of TSLAG crystal,respectively.And the life time of the TSLAG crystal has been measured to be 14.7 ?s.Finally,an optical isolator based on a TSLAG rotator has been demonstrated successfully,indicating the mature development of TSLAG crystal for Faraday rotator applications.In addition,modified growth have been carried out by considering the terms of seed,crucible and raw materials.High quality TSLAG crystals with dimessions of 35×60 mm3 have been successfully grown by using 60 mm caliber crucible.The enhanced Verdet constant has reached 1.2 times of TGG crystal,and improved isolators with modified TSLAG crystals are expected to be further enhance.