Herbert W. Newkirk

Laser performance of LiSrAlF6:Cr3+

We have lased the new material, LiSrAlF6:Cr3+ (Cr3+:LiSAF). The single crystals were grown by the horizontal zone melting technique. The spectroscopic properties of Cr3+:LiSAF are similar to those of other low‐field Cr3+‐doped systems, although the emission cross section is strongly π polarized and is also somewhat larger than has been measured for other fluoride hosts. The free‐running lasing wavelength of Cr3+:LiSAF is 825 nm, and the tuning range extends from at least 780 to 920 nm. Using Kr laser pumping, we obtained slope efficiencies of 36% and 14% by utilizing output couplings of 4.8% and 0.8%, respectively. On the basis of these results, the extrapolated maximum efficiency of 53% is determined, to be compared to the quantum defect‐limited value of 78%. It is concluded that a moderate level of excited state absorption (ESA) loss is responsible for the reduced efficiency of the Cr3+:LiSAF system. This contrasts with the related results previously obtained for LiCaAlF6:Cr3+, where it was concluded th...

LiCaAlF/sub 6/:Cr/sup 3+/: a promising new solid-state laser material

LiCaAlF/sub 6/:Cr/sup 3+/ (Cr/sup 3+/:LiCAF) exhibits an intrinsic (extrapolated maximum) slope efficiency of 67%. For comparison, the intrinsic slope efficiencies of BeAl/sub 2/O/sub 4/:Cr/sup 3+/ (alexandrite), Na/sub 3/Ga/sub 2/Li/sub 3/F/sub 12/:Cr/sup 3+/ and ScBO/sub 3/:Cr/sup 3+/ were found to be 65, 28, and 26%, respectively. The tuning range of LiCaAlF/sub 6/:Cr/sup 3+/ was determined to be at least 720-840 nm. The conventional spectroscopic properties, such as the absorption, emission, and emission lifetimes as a function of temperature, are reported as well. >

Electrical Transport Processes in Beryllium Oxide

The electrical resistivity was determined for polycrystalline and single‐crystal BeO between 1200°–1700°C. Analysis was made of the effects of oxygen partial pressure, aliovalent impurities, and microstructure. Conductivity and relevant diffusion coefficients were calculated with these data. The results show the BeO samples to be impurity‐controlled ionic conductors, and establish the need for higher‐purity material to study intrinsic properties. Electrical migration is independent of grain boundaries and crystallographic direction. Creation of cation defects by varying the oxygen activity in the specimens is not an important process in this material. At high temperatures, above a critical roll‐over temperature determined by the impurity content, electrical transport processes occur by a vacancy mechanism with an activation energy of 65 ± 5 kcal/mole. At lower temperatures, the electrical transport process is more complex and no simple theory is applicable. It is suggested that precipitation of impurities...

Optical properties of LaMgAl11O19:Cr,Nd*

The optical properties of Cr‐doped LaMgAl11O19 (LMAO:Cr) and LMAO:Cr,Nd have been measured. Evidence of Cr to Nd radiationless energy transfer was observed. Since LMAO:Nd may become a useful laser material, the prospect of further improving laser performance through Cr‐sensitization is discussed.

Laser Performance and Spectroscopy of Cr3+ in LiCaAlF6 and LiSrAlF6

We comprehensively report on the laser measurements and relevant spectroscopic properties of the materials LiCaAlF6:Cr3+ (Cr:L1CAF) and L1SrAlF6:Cr3+ (Cr:LiSAF). Laser-pumped laser measurements show that slope efficiencies of >50% are attainable with currently available Cr:LiCAF material, and that efficiencies of 67% should ultimately be achievable. Efficiencies of 36% have been measured for Cr:LiSAF. The absorption and emission properties, and the direct measurements of the excited state absorption loss, support the data concerning the lasing efficiencies and tuning ranges. Flashlamp-pumped operation of Cr:LiCAF has provided electrical efficiencies of 1.55% thus far, and we expect to obtain performance comparable to that of alexandrite in the future (which is 4% efficiency 1n the present apparatus).