Yb:YAG ceramic laser materials, fabricated by vacuum sintering technology, were
optically investigated within different laser set-up configurations. The established nanopowder
vacuum sintering process shows good potential for mass fabrication of multicomposite
ceramic laser materials with different dopant concentrations. 5%, 7%, 10%
single dopant and 7%/20% core-cladding multi-composite Yb:YAG materials were
fabricated and investigated. The highest measured slope efficiency, for the composite
ceramic laser materials was 81%, at 1030 nm emission wavelength, similar to Yb:YAG
We have investigated a relationship among the bulk laser-induced damage threshold (LIDT) and YAG ceramics
with various structural defects. The correlation of scattering defect density and laser damage resistance was clearly
observed. A high-quality YAG ceramic having a low-scattering density showed a higher LIDT than that of a low-quality
YAG ceramic. Laser damage threshold (LIDT) of high-quality YAG ceramic was almost the same as that of a single
crystal. In addition, the high-quality Nd:YAG ceramics with
low-defect density showed an excellent oscillation
efficiency which was comparable to that of a single crystal. Thus, high-quality YAG ceramic with low-defect density is
more reliable as a material which is highly resistant to laser damage.
Remote monitoring of carbon dioxide (CO<sub>2</sub>) is becoming increasingly
important for homeland security needs as well as for studying the CO<sub>2</sub>
distribution in the atmosphere as it pertains to global warming problems.
So, efficient solid-state lasers emitting in the 1.55 - 1.65 μm spectral
range, where CO<sub>2</sub> absorption lines are, (i), plentiful and, (ii), carry
significant relevant information, are in great demand. Reported here is the
first laser performance of resonantly pumped Er<sup>3+</sup>-doped scandia (Sc<sub>2</sub>O<sub>3</sub>)
ceramic. The laser was operated in the cryogenically-cooled regime with
the quantum defect (QD) of only 4.5%, which, along with superior thermal
conductivity of scandia, offers significant eye-safe power scaling potential
with nearly diffraction limited beam quality. Slope efficiency of 77% and
Q-CW output power of 2.35 W were obtained at 1605.5 nm which has
significant utility for counter-IED applications.
Edge-pumping Nd:YAG laser gain media is a convenient method to couple pump power into a laser cavity. A difficulty with this geometry is that for uniformly doped materials, pump power deposited near the edge of the gain medium cannot be efficiently extracted by a diffraction-limited beam. However, ceramic Nd:YAG with smooth changes in neodymium doping level (doping profiles) can now be fabricated to ameliorate this problem. A slab engineered with a doping profile that has a higher concentration of Nd in the center, and less at the edges, would allow more pump power to be efficiently extracted by a diffraction-limited laser beam. Yet this solution poses its own problem because variations in Nd concentration introduce optical path length distortions that can significantly reduce beam quality. The variations in optical path length are predominantly from changes in the refractive index of the host due to Nd doping and spatially varying temperatures. A genetic-algorithm-based approach is presented that balances improvement in mode-overlap between excited state distribution and the signal laser beam against optical path length distortions. A doping profile was found for an edge-pumped, zig-zag slab amplifier that is expected to yield a 39% improvement in extracted power delivered into a diffraction-limited spot compared to a uniformly doped slab.
The spectroscopic investigation of the highly transparent rare earth (Pr<sup>3+</sup>, Nd<sup>3+</sup>, Ho<sup>3+</sup>, Er<sup>3+</sup>, Tm<sup>3+</sup>, Yb<sup>3+</sup>) doped Sc<sub>2</sub>O<sub>3</sub>
ceramics produced by the solid-state synthesis technique indicate that these materials could substitute the single crystals
in construction of solid-state lasers. These studies indicate also that the rare earth doped transparent ceramics could
extend considerably the variety and performances (new active systems, wavelength ranges or emission schemes) of these
We report the first demonstration of polycrystalline Nd:YAG (Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>), and Nd-doped YAG single crystal with almost perfect pore-free structure by advanced ceramic processing. The laser conversion efficiency of pore-free polycrystalline Nd and Yb doped ceramics is extremely high, and their optical qualities are comparable to that of commercial high quality Nd:YAG single crystal. We have succeeded also in the fabrication of Nd:YAG single crystal, which can be used for laser oscillation, by solid-state reaction method. Laser oscillation efficiency was very low when pores were remained inside single crystal, however the laser oscillation efficiency of pore-free Nd:YAG single crystal was slightly higher than that of polycrystalline Nd:YAG ceramics having high optical quality. From this fact, it was recognized that the optical scattering occurs mainly at the residual pores inside the Nd:YAG ceramics, and the scattering at the grain boundary is very little. In addition, we confirmed that Nd heavily-doped YAG single crystal can be fabricated by sintering method. We have demonstrated the fabrication of composite ceramic with complicated structures without the needs of precise polishing and diffusion bonding. Advanced ceramic processing, which enables design flexibility of laser element, presented in this work is important in the development of high performance laser (high efficiency, high beam quality and high output energy etc.) Moreover, we have recently developed polycrystalline ceramic fiber laser first in the world, and achieved over 8W output per unit length of the fiber.
The information on the variety, nature and structure of the centers formed by the rare earths ions doped in the transparent laser ceramics of garnets and cubic sesquioxides, acquired from high-resolution spectroscopy and emission decay is analyzed. The quantum states (energy levels, transition probabilities) of several doping rare earth ions, their distribution at the available lattice sites, the interactions between ions, and energy transfer processes are also presented. It is inferred that from spectroscopic point of view these materials could substitute the melt-grown single crystals in construction of solid-state lasers and extend considerably their capabilities.
We report a 1.2 at. % Nd:YAG ceramic pumped with an 808-nm laser diode, placed in a
1.92-m cavity, and passively mode-locked at 1064-nm with a 1% modulation depth
SESAM. At a pump power of 11.1 W, this laser produced 2.6 W of average power with a
slope efficiency of 27%. The pulse length was 26 ps at a repetition rate of 78 MHz. The
ceramic exhibited no peak power degradation during a 20-hour test of doubling efficiency
with periodically-poled, near-stoichiometric lithium tantalate.
Highly transparent Nd- or (Nd,Yb)-doped Sc<sub>2</sub>0<sub>3</sub> ceramics are produced by the method of solid-state mixing of oxides. High-resolution spectroscopy indicates the spectroscopic and structural properties of the doping ions in these ceramics are similar with those of single crystals, although the maximum doping could be much higher. Very efficient Nd-to-Yb energy transfer is observed, which can be used for sensitisation of Yb laser emission.
There has been considerable interest in the trivalent rare earth-ion-doped ceramic laser materials because of its numerous advantages over melt growth methods, including faster production times, solid solution allowing the fabrication of multi-phase transition materials, highly homogeneous materials and the ability to engineer profiles and structures before sintering. Much progress has been made in improving the optical quality from ceramics, as well as exploring new materials. Successfully developed concentrated Nd:YAG ceramics was opened the way for drastic heat reduction by directly upper laser level pumping. In this present, after the spectroscopic investigation of rare-earth doped garnet materials includes ceramics, we report about the heat generation properties with the radiative quantum efficiency. Lately developed RE<sup>3+</sup>-ion-doped disordered laser ceramic materials, Y<sub>3</sub>Sc<sub>x</sub>Al<sub>5-x</sub>O<sub>12</sub>, which are a solid solution of YAG and Y<sub>3</sub>Sc<sub>2</sub>Al<sub>3</sub>O<sub>12</sub> (YSAG), have been interested in because of its compositional tuning of parameter <i>x</i>. The disordered Y<sub>3</sub>ScAl<sub>4</sub>O<sub>12</sub> (YAG/YSAG) ceramics exhibit relatively low minimum pump intensity (<i>I</i><sub>min</sub>) and broad emission bandwidth. The value of <i>I</i><sub>min</sub> in the Yb:Y<sub>3</sub>ScAl<sub>4</sub>O<sub>12</sub> ceramics was found to be 2/3 compared with the Yb:YAG single crystal under 970nm zero-line pumping. Efficient laser oscillation of 72% slope efficiency was
obtained for input power. Next, we have demonstrated passively mode-locked Yb:Y<sub>3</sub>ScAl<sub>4</sub>O<sub>12</sub> disordered ceramic laser by using a semiconductor saturable-absorber mirror. Pulses as short as 280 fs having an average power of 62 mW at 1035.8 nm was obtained. As a conclusion, the possibility of tailored fluorescence spectral profile in layer-by-layer type ceramic composite will be discussed.
We report the first demonstration of polycrystalline Nd-doped YAG ceramics with almost perfect pore-free structure and Nd-doped YAG single crystal by advanced ceramic processing. The laser conversion efficiency of pore-free polycrystalline Nd:YAG ceramics is extremely high and its optical quality is comparable to that of commercial high quality Nd:YAG single crystal. Moreover, we have succeeded also in fabrication of Nd:YAG single crystal, which enables laser oscillation, by solid-state reaction method. Laser oscillation efficiency was very low when the pores were remained inside single crystal, however the laser oscillation efficiency of pore-free Nd:YAG single crystal was slightly higher than that of polycrystalline Nd:YAG ceramics having grain boundaries. From this fact, it was found that the optical scattering inside the Nd:YAG ceramics occurs mainly at the residual pores and the scattering at the grain boundary is very little. In addition, we confirmed that high concentration Nd:YAG single crystal can be fabricated by sintering method. Applying the above single crystallization technology by sintering method, we have demonstrated the fabrication of layer-by-layer single crystal composite and micron size spherical single crystal.
Since the composite laser media using single crystal such as Nd:YAG and undoped YAG was reported in 1998, the composite with various structures provided to experimental or industrial field. However, conventional bonding condition is not enough for laser application, and fabrication process is extremely complex and long delivery owing to necessity of polishing and diffusion bonding. Ceramic composite laser gain media having layer by layer and clad-core structure were fabricated successfully for the first time by advanced ceramic processing. Advanced ceramic technology provides a direct formation of composite having complex structure without polishing and diffusion bonding. The bonding condition of ceramic composite was confirmed to almost optically perfect, so we could oscillate successfully using composite laser media.
Spectroscopic and emission decay investigation on single crystal Nd:YAG (with up to 3at.%Nd) and transparent ceramic (up to 9at.%Nd) samples indicate that the state of Nd ions (the sites occupied by the Nd ions, the crystal field and electron-phonon interactions, energy transfer between the Nd ions) are identical. Coupled with the similarity of the thermo-mechanical properties and with specific features of ceramics, such as a high production yield, possibility to produce very large components with uniform Nd doping up to very high concentrations, reduced production cost, these studies show that the transparent ceramic Nd:YAG can be used for construction of lasers. These conclusions are supported by efficient laser emission data.
Transparent YAG ceramics with nearly the same optical characteristics as those of a single crystal were fabricated by a solid-state reaction method using high-purity powders. The average grain size and relative density of the 1.1 at % Nd:YAG ceramics obtained were about 50 micrometers and 99.98% respectively. An oscillation experiment was performed on a cw laser by the diode laser excitation system using the fabricated ceramics. The experimental results indicated an oscillation threshold and a slope efficiency of 309 mW and 28% respectively. These values were equivalent or superior to those of 0.9 at % Nd:YAG single crystal fabricated by the Czochralski (CZ) method.