Font Size: a A A

Spectral And Laser Properties Of Novel Nd-doped Vanadate And Silicate Crystals

Posted on:2015-03-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y G ZhaoFull Text:PDF
GTID:1268330431955156Subject:Condensed matter physics
Abstract/Summary:PDF Full Text Request
As a key part of the laser, laser materials are always in the spotlight of scientific interest. Up to now, Nd-doped vanadate and silicate crystals have been demonstrated to be two prominent gains mediums, since they have excellent optical, mechanical and chemical properties. For the vanadate crystals, such as Nd:YVO4, Nd:LuVO4and Nd:GdVO4, they are the primary materials in the diode pumped solid state laser with middle to low output power, because of their large absorb and emission cross-sections. However, the relatively large emission cross-section and short up-level lifetime have constrained their application in Q-switched lasers because it requires a large energy storage capacity, which in turn demands a small emission cross section and a long fluorescence lifetime. So, the vanadate mixed crystals (including Nd:GdxY1-xVO4、 Nd:Lux-Gd1-xVO4and Nd:LuxY1-xVO4) were grown and researched recently. Previous laser experiments have demonstrated that the stimulated emission cross-sections decreased and fluoresces lifetime increased in the mix crystals, which can enhance the energy storage capacity. In essence, it is caused by the inhomogeneous spectrum broadening of Nd3+ions in the mixed crystals. However, the direct research on the inhomogeneous spectrum broadening effect has never been reported. In chapter2, a study of inhomogeneous spectrum broadening in Nd3+-doped mixed crystals (GdxY1-xVO4, LuxGd1-xVO4and LuxY1-xVO4) is reported for the first time. Due to the random placement of different cations in the lattice, the spectra are inhomogeneously broadened, which is beneficial for both Q-switching and mode locking. For all the samples, as increasing the temperature, the spectrum broadened and emission peak presented "red shifted". Using traditional crystals (Nd:LuVO4, Nd:YVO4or Nd:GdVO4) as the reference, the inhomogeneous spectrum broadening caused by the random replacement can be obtained at77K. The largest spectrum width and longest lifetime are obtained by the same component. They are Nd:Gd0.63Y0.37VO4, Nd:Lu0.5Gd0.5VO4and Nd:Lu0.61Y0.39VO4crystals, respectively. All the results indicate that the random placement of different cations at the same lattice site is an efficient technology for the modification of emission properties that fulfill different requirements of laser applications.Recently, some research have demonstrated the large energy storage capacity and short mode-locking laser pulses of the Nd:GdxY1-xVO4and Nd:LuxGd1-xVO4mixed crystals. Combine with the property of the emission spectrum, we reported the Q-switching, mode-locking and self-stimulated Raman laser characteristics of the novel Nd:LuxY1-xVO4crystal in chapter3. For the1.06μm passively Q-switched laser, the shortest pulse width, the largest pulse energy and the highest peak power were found to be1.9ns,104.7μJ and55.1kW, respectively, using c-cut Nd:Lu0.1Y0.9VO4crystal as the laser gain and a Cr4+:YAG crystal as the saturable absorber. For the1.3μm acousto-optic (A-O) Q-switching laser operation, the shortest pulse width, largest pulse energy, and highest peak power were23.8ns,124μJ, and5.21kW, respectively, obtained by the a-cut Nd:Lu0.1Y0.9VO4crystal. In this chapter, the1175-nm A-0Q-switched self-Raman laser of Nd:LuxY1-xVO4crystal was also demonstrated for the first time. Combining the advantages of mixed vanadate crystal and c-cut orientation, the c-cut Nd:Lu0.1Y0.9VO4crystal exhibited prominent self-Raman laser characteristics, such as101μJ single pulse energy,1.3ns pulse width, and78kW peak power. With the largest thermal conductivity, excellent energy storage capability and moderate Raman gain coefficient, the a-cut Nd:Lu0.26Y0.74VO4crystal presented the largest average output power of2.3W. With a semiconductor saturable absorber mirror (SESAM), the passively mode-locking of this series crystal was carried out under the same condition. The shortest pulse was obtained by the Nd:Lu0.61Y0.39VO4crystal, which indirectly manifested the widest line-width of this component and its excellent properties for pulse laser applications.Previous researches about LYSO have been focused on scintillator applications and Yb-doped lasers. Research about the Nd-doped LYSO was mainly focus on the crystal growth and simple laser experiment. Chapter4mainly discussed the the anisotropy of laser emission in the monoclinic, disordered crystal Nd:LYSO. According to the polarized emission spectrum, we calculated the spatial distribution of the stimulated emission cross-sections for the first time. Then the output characteristic is well explained by a theoretical analysis on the stimulated emission cross-section. This work reveals that the intrinsic anisotropy in disordered laser crystal can be utilized to elevate the emission controllability. Accordantly, the material’s application scopes can be extended. Using multilayered graphene as the saturable absorber (SA), Nd:LYSO crystal as the laser material, we demonstrated a laser-diode (LD) pumped, dual-wavelength passively Q-switched solid-state laser. The maximum average output power is1.8W, the largest pulse energy and highest peak power is11.3μJ,118W, respectively. The results are2-4orders of magnitude of the corresponding values that obtained in the fiber laser. As we have known, they are also the best results for passively Q-switched operation of grapheme in all solid-stated lasers. The pulse laser is strong enough to realize extra-cavity frequency conversions, which manifests the synchronous modulation to the dual-wavelength with multi-layered grapheme, and the possibility of its practical.Chapter5demonstrated the direct generation of1.08μm optical vortex pulses in a simple and compact two-mirror laser cavity for the first time, with Nd:LYSO crystal as laser gain material. Single Laguerre-Gaussian (LG0,1) laser modes were directly generated using a laser diode with output intensity profile of doughnut distribution. With passive Q-switching, vortex pulses with stable energy were obtained. Moreover, the topological charge was changeable by variation of the pump power. By a mode-converter and second harmonic generation, the LG0,21mode was identified. In order to know the generation of the vortex and its changing, we demonstrated the continuous-wave (cw) and pulse optical vortex operation at1.36μm. During the lasing process, the topological charges were changeable by the thermal-induced lens and selected by the mode-matching between the pump and oscillating beams. With a graphene sample as the saturable absorber, the pulsed optical vortex was achieved, which identified that graphene could be used as a pulse modulator for the generation of pulsed optical vortex. It could be believed that the thermally driven cw and pulsed optical vortex should have various promising applications based on the compact structure, changeable topological charges and specific wavelength.
Keywords/Search Tags:solid-state laser, inhomogeneous spectrum broadening, anisotropy, opticalvortex, vanadate mixed crystal, silicate mixed crystal
PDF Full Text Request
Related items