Akio Ikesue

Optical properties and laser characteristics of highly Nd3+-doped Y3Al5O12 ceramics

Diode-pumped laser oscillation in highly Nd3+-doped polycrystalline Y3Al5O12 (YAG) ceramics has been demonstrated. The Nd:YAG ceramics are highly transparent; the loss of a 2.3 at. % neodymium-doped ceramic is as low as that of a 0.9 at. % Nd:YAG single crystal. The high doping of Nd3+ ions realizes large pump absorption; a 6.6 at. %-doped ceramic has an absorption coefficient of 60.4 cm−1 at 808 nm. The same concentration quenching parameter is obtained between the Nd:YAG ceramics and Nd:YAG single crystals. A laser using an 847-μm-thick 3.4 at. % Nd:YAG ceramic as a gain medium operates at 2.3 times higher output power than the same laser with a 719-μm-thick 0.9 at. % Nd:YAG single-crystal gain medium.

Three-dimensional grain boundary spectroscopy in transparent high power ceramic laser materials.

Using confocal Raman and fluorescence spectroscopic imaging in 3-dimensions, we show direct evidence of inhomogeneous Nd(3+) distribution across grain boundaries (GBs) in Nd(3+):YAG laser ceramics. It is clearly shown that Nd(3+) segregation takes place at GBs leading to self-fluorescence quenching which affects a volume fraction as high as 20%. In addition, we show a clear trend of increasing spatial inhomogeneities in Nd(3+) concentration when the doping levels exceeds 3 at%, which is not detected by standard spectrometry techniques. These results could point the way to further improvements in what is already an impressive class of ceramic laser materials.

Thermal-birefringence-induced depolarization in Nd:YAG ceramics

The thermal-birefringence effect in Nd(3+) -doped YAG ceramics has been investigated. The amount of depolarization induced by thermal birefringence in Nd:YAG ceramics is nearly the same as that in (111)-cut single crystals at the same Nd(3+) concentration. However, depolarization becomes larger as the Nd(3+) concentration increases, even at the same absorbed pump power.

Ultralow quantum-defect eye-safe Er:Sc2O3 laser.

Resonantly pumped Er(3+):Sc(2)O(3) laser operation is achieved with a quantum defect (QD) of 1.5% at liquid nitrogen temperature. The laser, in-line pumped at 1535 nm, operated at 1558 nm with a slope efficiency of over 45%. This is believed to be the lowest QD eye-safe laser ever reported. CW output of over 3.3 W was obtained in this first experiment.

Spectral Parameters of Nd3+-ion in the Polycrystalline Solid-Solution Composed of Y3Al5O12 and Y3Sc2Al3O12

We have fabricated the Nd3+-doped mixed structure, Y3ScxAl5-xO12, polycrystals by the sintering method and studied them spectroscopically as potential laser media. Using the Judd-Ofelt theory to analyze the optical strength measured in absorption spectra, the parameters of oscillator strengths and fluorescence branch ratios were calculated and found to have a linear dependence on the compositional parameter x.

Resonantly diode-pumped Ho 3+ :Y 2 O 3 ceramic 2.1 µm laser

We report what is believed to be the first laser operation based on Ho3+-doped Y2O3. The Ho3+:Y2O3 ceramic was resonantly diode-pumped at ~1.93 µm to produce up to 2.5 W of continuous wave (CW) output power at ~2.12 µm. The laser had a slope efficiency of ~35% with respect to absorbed power and a beam propagation factor of M2 ~1.1. We have measured the absorption and stimulated emission cross sections of Ho3+:Y2O3 at 77 K and 300 K and present the calculated gain cross section spectrum at 77 K for different excited state inversion levels.

Passive mode locking of a mixed garnet Yb:Y3ScAl4O12 ceramic laser

We have demonstrated a passively mode-locked Yb3+-doped Y3ScAl4O12 ceramic laser, which is a solid solution of Y3Al5O12 and Y3Sc2Al3O12, by using a semiconductor saturable-absorber mirror. The maximum average output power was as high as 150 mW with a pulse duration of 500 fs. With a 0.5% output coupler, pulses as short as 280 fs having an average output power of 62 mW at 1035.8 nm were obtained.

Experimental study of thermally induced depolarization in Nd:YAG ceramics

Spatial modulation of a laser beam with a transverse size of the order of one grain size is experimentally found at thermal depolarization in Nd:YAG ceramics. This effect, which was theoretically predicted earlier, is typical for ceramics only, with no analogs either in glasses or in single crystals.

Tailored Spectral Designing of Layer-by-Layer Type Composite Nd:Y

We have proposed an optical design by tailoring a spectral profile in a ceramic composite of layer-by-layer type Nd:Y3Al5O12/Nd:Y3ScAl4O12. The composite ceramics with enough optical properties to amplify the stimulated emission were fabricated by the sintering method with solid state reaction. After the investigation of spectroscopic property, the laser oscillation was demonstrated with slope efficiency of 39% by using an un-coated sample. This paper shows that novel developments in the technology of composite ceramics are useful because they offer a new possibility of existing laser materials.

_{3}

Diode-pumped microchip laser oscillation of highly Nd3+-doped polycrystalline YAG ceramics has been realized. The loss of a 2.3 at. % Nd3+-doped ceramic YAG is as low as that of a 0.9 at. % NdYAG single crystal. Using a 3.4 at. % NdYAG ceramic, 2.3 times higher microchip laser power is obtained than with a 0.9 at. % Nd:YAG single crystal.