Giorgio Turri

Temperature-dependent stimulated emission cross section in Nd 3+ :YVO 4 crystals

Spectroscopic properties of neodymium-doped yttrium orthovanadate crystals were measured in the temperature range between 5 and 350 K. Crystals fabricated by different suppliers, with 0.3 and 1 at% Nd3+, were compared. For each temperature, the stimulated emission cross sections of the Nd3+ 4F3/2 decay to the 4I9/2, 4I11/2, and 4I13/2 states were obtained using the Fuchtbauer-Ladenburg and the reciprocity techniques. Nd:YVO4 shows higher absorption at room temperature and higher stimulated emission cross section with similar variation with temperature when compared with Nd:YAG. The anomalous dependence on temperature of the Nd3+ 4F3/2 excited-state lifetime is discussed and an explanation is suggested.

Temperature-dependent spectroscopic properties of Tm3+ in germanate, silica, and phosphate glasses: A comparative study

Spectroscopic properties of thulium-doped germanate, silica, and phosphate glasses were measured and compared since such glasses are of interest as materials for fiber lasers in the eye-safe wavelength region. F43 excited state fluorescence decay dynamics was investigated at temperatures from 8to300K and the results revealed a strong dependence of the F43 lifetime on the host matrix. The temperature-dependent stimulated emission cross section was obtained by using the Fuchtbauer–Ladenburg technique. In phosphate glass the fluorescent lifetime is short, making this material difficult to use for 2μm laser purposes. Tm3+-doped germanate glass shows a longer lifetime than silica, a comparable value of stimulated emission cross section and some interesting temperature-independent properties.

Optical Absorption, Depolarization, and Scatter of Epitaxial Single-Crystal Chemical-Vapor-Deposited Diamond at 1.064 μm

Epitaxial single-crystal chemical-vapor-deposited diamond with (100) crystal orientation is obtained from Element Six (Ascot, United Kingdom) and Apollo Diamond (Boston, Massachusetts). Both companies supply 5×5-mm squares with thicknesses of 0.35 to 1.74 mm. Element Six also provides disks with a state of the art diameter of 10 to 11 mm and a thickness of 1.0 mm. The absorption coefficient measured by laser calorimetry at 1.064 μm is 0.003 cm -1 for squares from Element Six and 0.07 cm -1 for squares from Apollo. One Apollo specimen has an absorption coefficient near those of the Element Six material. Absorption coefficients of Element Six disks are 0.008 to 0.03 cm -1 . Each square specimen can be rotated between orientations that produce minimum or maximum loss of polarization of a 1.064-μm laser beam transmitted through the diamond. Minimum loss is in the range 0 to 11% (mean=5%) and maximum loss is 8 to 27% (mean=17%). Element Six disks produce a loss of polarization in the range 0 to 4%, depending on the angle of rotation of the disk. Part of the 0.04 to 0.6% total integrated optical scatter in the forward hemisphere at 1.064 μm can be attributed to surface roughness.

Influence of modifier oxides on the structural and optical properties of binary TeO2 glasses

Five different glass compositions with equal TeO2 molar concentration and various intermediate constituents were prepared to examine the influence of such intermediate species on the tellurite network. A correlation between the glasses’ structural network and optical properties is presented. Peak Raman gain coefficients, on the order of 40 times the gain of SiO2, are reported in this paper.

Index of Refraction from the Near-Ultraviolet to the Near-Infrared from a Single Crystal Microwave-Assisted CVD Diamond

The refractive index of a type IIa CVD-grown single-crystal diamond was measured by ellipsometry from the near ultraviolet to the near infrared region of the spectrum. As a consequence, a one term Sellmeier Equation with coefficents of B1 = 4.658 and C1 = 112.5 for the refractive index of diamond, for the wavelength range from 300 to 1650 nm, was derived that is only as accurate as the input data, +/− 0.002. The experimental results in this paper between 800 and 1650 nm are new, adding to the values available in the literature.

Spectral engineering of optical fiber preforms through active nanoparticle doping

Europium doped alkaline earth fluoride [Eu:AEF2 (AE = Ca, Sr, Ba)] nanoparticles were synthesized and systematically incorporated into the core of modified chemical vapor deposition (MCVD)-derived silica-based preforms by solution doping. The resulting preforms were examined to determine the impact of the nanoparticles chemistry on the spectroscopic behavior of the glass. The dominant existence of Eu3+ was demonstrated in all preforms, which is in contrast to conventional solution doped preforms employing dissolved europium salts where Eu2+ is primarily observed. Raman spectroscopy and fluorescence lifetime measurements indicated that the nanoparticles composition is effective in controlling, at a local chemical and structural level, the spectroscopic properties of active dopants in optical fiber glasses. Further, there is a systematic and marked increase in radiative lifetime, τ, of the Eu3+ emission that follows the cationic mass; τCa < τSr < τBa with the BaF2-derived sample yielding a 37% lengthening of the lifetime over the CaF2-derived one. Such nanoscale control of what otherwise is silica glass could be useful for realizing property-enhanced and tailored spectroscopic performance from otherwise “standard” materials, e.g., vapor-derived silica, in next generation optical fibers.

Spectroscopic comparison of Nd:BaYLuF 8 and Nd:BaY 2 F 8

We grew oriented single crystals of BaYLuF8 and Nd:BaY2F8 doped with Nd3+. An experimental investigation and comparison of the spectroscopic properties of the two crystals are presented to guide their use as lasing elements in solid-state lasers. The absorption and stimulated emission cross section of the Nd3+ 4F3/2 decay to the 4I9/2, 4I11/2 and 4I13/2 states, for light linearly polarized along the three principal axes, were obtained at room temperature. Nd:BaYLuF8 shows absorption and stimulated emission cross sections that are very similar to those of Nd:BaY2F8, making it a good candidate for lasers. Because Nd:BaYLuF8 is easier to grow than Nd:BaY2F8, it is a viable alternative as a laser medium.

Development of High-Purity Optical Grade Single-Crystal CVD Diamond for Intracavity Cooling

Microwave assisted chemical vapour deposited bulk diamond products have been used in a range of high power laser systems, due to low absorption across a range of wavelengths and exceptional thermal properties. However the application of polycrystalline products has frequently been limited to applications at longer wavelengths or thermal uses outside of the optical path due to the birefringence and scatter that are intrinsic properties of the polycrystalline materials. However, there are some solid state structures, including thin disc gain modules and amplifiers, that will gain significantly in terms of potential output powers if diamond could be used as a heat spreader in the optical path as well as a heat spreader on the rear surface of the disk. Therefore single crystal grades of diamond have been developed that overcome the limitations of the polycrystalline material, with low absorption, low scatter and low birefringence grades for demanding optical applications. We will present new data, characterising the performance of these materials across infra-red and visible wavelengths with absorption coefficient measured by laser calorimetry at a range of wavelengths from 1064 nm to 452 nm.

Optical properties of epitaxial single-crystal chemical-vapor-deposited diamond

Epitaxial single-crystal chemical-vapor-deposited diamond was obtained from Element Six Ltd. (Ascot, UK) and from Apollo Diamond (Boston, MA). Both companies provided 5 x 5 mm squares with thicknesses ranging from 0.5 to 1.5 mm. In addition, Element Six provided 10-mm-diameter disks with a thickness of 1.0 mm. The absorptance of all specimens at 1064 nm was measured by laser calorimetry, with good agreement between independent measurements at the University of Central Florida and at QinetiQ (Malvern, UK). Depolarization at 1064 nm and ultraviolet absorption properties are also reported.

Spin polarization of the Ar* 2p−11/2 4s and 2p−11/2 3d resonant Auger decay

The spin-resolved Auger decay of the Ar 2p−11/2 3d state was measured at moderate energy resolution and compared with the decay of the 2p−11/2 4s. The former shows a lower transferred spin polarization and a similar, if not higher, dynamical spin polarization, supporting the statement that a fully resolved spectrum is not a necessary condition for observing dynamical spin polarization. An interpretation of the spin polarization as configuration interaction induced effect in the final ionic state leads to partial agreement with our relativistic distorted wave calculation utilizing a 36 configuration state function basis set. Comparison of the experimental and numerical results leads to ambiguities for at least one Auger line. A hypothetical, qualitative interpretation is discussed.