Masami Sekita

Induced emission cross section of Nd:Y3Al5O12 ceramics

Optical absorption and emission spectra have been measured for Nd‐doped Y3Al5O12 ceramics obtained by a urea precipitation method. The optical properties of the ceramics are almost the same as those of single crystals grown by the Czochralski method and floating‐zone method, except for a higher background absorption of 2.5–3 cm−1. The energy‐level structure for Nd3+ in the Y3Al5O12 ceramics is determined for a 1‐at. % Nd concentration. The induced emission cross section for the 1‐at. %‐Nd‐doped ceramic is calculated to be 4.9×10−19 cm2, which falls in the range reported for the Nd:Y3Al5O12 single crystals. The Nd concentration dependence of the emission decay time at the 1064‐nm laser wavelength was also measured, and typical concentration quenching was observed. The decay time of the 1‐at. %‐Nd‐doped ceramic is 219 μs, which is slightly smaller than the reported values for single crystals.

Carbon nanofilm with a new structure and property

We have prepared a carbon film of nanometer thickness, which is called here a carbon nanofilm (CNF), starting from the oxidation of graphite. The structure and thickness of the CNF are determined by high-resolution transmission electron microscopy and electron diffraction. The structure is of a new type (S.G.: P3), in which carbon six-membered-ring planes are stacked with the sequence of ...AA.... According to electron energy loss spectroscopy, a substantial amount of oxygen is detected but the molar ratio of oxygen to carbon is possibly decreased to less than 0.1. The CNF changes from an insulator to a semiconductor when reduced on heating at 250°C.

OPTICAL SPECTRA OF UNDOPED AND RARE-EARTH-( = PR, ND, EU, AND ER) DOPED TRANSPARENT CERAMIC Y3AL5O12

Undoped and rare‐earth‐ (Pr, Nd, Eu, and Er) doped transparent Y3Al5O12ceramics have been prepared, and their optical spectra have been measured. It is found that absorption coefficient of the undoped ceramic Y3Al5O12 is almost independent of wavelength with 0.258 cm−1, which gives transmittance of the undoped ceramic Y3Al5O12 to be, for example, 95% for a 2‐mm height. Peaks in the absorption and emission spectra of Pr:Y3Al5O12 are assigned to the transitions in 4f 2 configuration. The transitions from the multiplets with total angular momentumJ=0 to multiplets with even J momentum are strong as predicted by Judd–Ofelt theory. The overall and detail structure of the absorption and emission spectra of Nd:Y3Al5O12 is the same as those in a previous publication. However, the absorption coefficient at nonabsorbing wavelengths by Nd3+ is reduced from more than 1.7 to 0.25 cm−1. A simple estimation of the population inversion threshold of the Nd:Y3Al5O12ceramic reveals that the threshold is still about 25 times larger than that of single‐crystal Nd:Y3Al5O12. Peaks in the absorption and emission spectra of Er:Y3Al5O12ceramic are assigned to the transitions in 4f 11 configuration. The transition energies agree well with those reported for single‐crystal Er:Y3Al5O12 and the other hosts within 30 cm−1. A Stark splitting scheme for some multiplets has been constructed. Peaks in the emission, absorption, and excitation spectra of Eu:Y3Al5O12ceramic are assigned to the transitions in 4f 6 configuration. The transition energies are in very good agreement with those of single‐crystal Eu:Y3Al5O12 within 8 cm−1 for the emission peaks and 3 cm−1 for the absorption and excitation peaks. Spectralcharacteristics and derivation of a broad peak in the absorptionspectrum at around 280 nm are discussed in some detail.

STARK SPLITTING SCHEME AND AN INDUCED EMISSION CROSS SECTION OF TBALO3

Detailed absorption and emission spectra on TbAlO3 are measured at room temperature and liquid-nitrogen temperature. By decomposition of the spectra, the Stark splitting scheme is established for 7F6, 7F5, and 5D4 multiplets of Tb3+ ions in TbAlO3 together with the peak energies in the Fourier transform infrared spectrum at liquid-nitrogen temperature. The multiplets are split into their maximum number of levels, which shows that the point symmetry is low for the Tb3+ ion site in TbAlO3. An induced emission cross section is estimated using the results of decomposition at liquid-nitrogen temperature to be 3.55×10−19 cm2. This value is comparable to the cross sections reported for Nd:Y3Al5O12, which is a well known solid-state laser material. The population inversion threshold is also estimated for TbAlO3 in comparison with Nd:Y3Al5O12. It is found that the threshold value for TbAlO3 is only about three times larger than that for Nd:Y3Al5O12. This TbAlO3 may have the potential to be a laser material with a ...

A nondiamond phase at the interface between oriented diamond and Si(100) observed by confocal Raman spectroscopy

We have characterized bias-assisted chemical vapor deposition diamond using the nondestructive technique of confocal Raman spectroscopy to investigate the interfacial structures and the variation in structure and quality with depth. The spectral depth profiles of oriented diamond showed that a band centered at 1210 cm−1 and the diamond peak at 1332 cm−1 coexisted at the interface between the oriented diamond and Si substrate. The relative intensity of the 1210 cm−1 band compared to that of the diamond peak varied with depth. The intensity of the band decreased and that of the diamond peak increased from the interface to the diamond surface. The quality of the oriented diamond improved with the growth time. In contrast, for the case of a randomly oriented diamond, a band centered at 1550 cm−1 was observed, the diamond peak was shifted between −6 and 6 cm−1 from the single crystal diamond peak at 1332.5 cm−1, and the spectral profile did not change with depth. No band at 1210 cm−1 was seen in this case. We ...

Interfacial structures of oriented diamond on Si(100) characterized by confocal Raman spectroscopy

Abstract We have characterized bias-assisted CVD diamond using the non-destructive technique of confocal Raman spectroscopy to investigate the interfacial structures and the variation in structure and quality with depth. The spectral depth profiles of oriented diamond showed that a band centered at 1210 cm−1 and the diamond peak at 1332 cm−1 coexisted at the interface between the oriented diamond and Si substrate. The relative intensity of the 1210 cm−1 band compared to that of the diamond peak varied with depth. The intensity of the band decreased and that of the diamond peak increased from the interface to the diamond surface. The quality of the oriented diamond improved with the growth time. In contrast, for the randomly-oriented diamond, a band centered at 1550 cm−1 was observed, the diamond peak was shifted between −6 and 6 cm−1 from the single crystal diamond peak at 1332.5 cm−1 and the spectral profile did not change with depth. No band at 1210 cm−1 was seen in this case. We conclude that a non-diamond phase with a Raman band at 1210 cm−1 and a diamond phase coexist at the interface between the oriented diamond and the Si substrate, and that this 1210 cm−1 phase is therefore a characteristic feature of the nature of the diamond-substrate bonding in oriented films. Speculations on the origin of the 1210 cm−1 are also discussed.

Induced emission cross section of Nd:Y3Al5O12 grown by floating zone method

Optical spectra and emission lifetimes are measured for three Nd:Y3Al5O12 crystals grown by the floating zone method. The properties are almost the same as those of crystals grown by the conventional Czochralski method. The induced emission cross sections obtained for the three samples are 7.4, 5.3, and 7.0×10−19 cm2. These values are comparable to those reported so far.

Induced emission cross section of a possible laser line in Nd:Y2O3 ceramics at 1.095μm

In this study, we measured the change of the optical transmittance for calcination temperatures, in steps of 10°, at two different sintering temperatures. It was found that the optical transmittance is highly dependent on the calcination temperature. The highest optical transmittance obtained was 70% for the transparent Y2O3 (yttria) ceramics produced without the use of additives and high injection presure in this study, higher than the highest reported value of 65%. Optical absorption and emission spectra of Nd:Y2O3 obtained from a low temperature synthesis process were measured. The energy level structure of Nd3+ in the Y2O3 ceramics was determined for a 1mol% Nd concentration. The induced emission cross section was calculated to be in the range of 3.2×10−19–1.1×10−17cm2 for the 1mol% Nd-doped Y2O3 ceramics. Furthermore, a laser line possibly has been identified in this study, in the Nd:Y2O3 ceramic at 1.095μm.

Stimulated emission cross section of Cr-doped GdScGa garnet

The stimulated emission cross section is calculated on the basis of emission spectrum and spontaneous lifetime measurements. The maximum stimulated emission cross section is determined to be 0.69×10−20 cm2. A comparison is made between the calculated stimulated emission cross section and one which has been determined from laser oscillation experiments. Fair agreement between them is obtained within a 20% error at wavelengths from 770 to 810 nm.

Induced emission cross sections of near-stoichiometric LiNbO3: Mg, Nd

Optical absorption and emission spectra are measured on Nd3+ ion in near-stoichiometric LiNbO3 single crystals codoped with MgO. From the decomposition of the nonpolarized spectra, the Stark splitting scheme is established for 2wt% Nd3+ ion in the near-stoichiometric LiNbO3:Mg, Nd system. The induced emission cross sections are calculated to be 2.70×10−19 and 5.57×10−20cm2 for the π and σ polarizations, respectively, based on the decomposition of the polarized spectra. These values agree well with the reported values of 1.8×10−19 and 5.1×10−20cm2 for the π and σ polarizations of the conventional congruent-melt composition crystal through the branching ratio of emission spectra despite the different approach of calculations and difference in the near-stoichiometric and congruent-melt compositions. This fact shows that the slight difference in the host composition does not affect the cross section. The population inversion threshold is calculated to be 2.0×1016 for the Nd(2wt%) near-stoichiometric LiNbO3:Mg...