Wayne L. Kway

Infrared cross-section measurements for crystals doped with Er/sup 3+/, Tm/sup 3+/, and Ho/sup 3+/

The absorption and emission cross sections of the transition between the ground spin-orbit multiplet and the lowest excited multiplet were measured for Er/sup 3+/, Tm/sup 3+/, and Ho/sup 3+/ ions in a variety of crystalline hosts. The materials that were investigated include LiYF/sub 4/, BaY/sub 2/F/sub 8/, Y/sub 3/Al/sub 5/O/sub 12/, LaF/sub 3/, KCaF/sub 3/, YAlO/sub 3/, and La/sub 2/Be/sub 2/O/sub 5/. The absolute magnitudes of the emission cross sections were determined from the absorption spectra, with the aid of the principle of reciprocity. The calculated radiative emission lifetimes derived from these measured cross sections agree well with the measured emission decay times for most materials. The potential use of these rare-earth-doped materials in pulsed laser applications requires that the ground state exhibit adequate splitting to minimize the detrimental effects of the ground state thermal population, and also that the emission cross section be sufficiently large to permit efficient extraction energy. The systems based on Ho/sup 3+/ in the eightfold coordinated sites of LiYF/sub 4/, BaY/sub 2/F/sub 8/, and Y/sub 3/Al/sub 5/O/sub 12/ appear to be the most promising. >

Evaluation of absorption and emission properties of Yb/sup 3+/ doped crystals for laser applications

The emission and absorption properties of numerous host crystals doped with Yb/sup 3+/ ions have been studied. The hosts which have been selected include LiYF/sub 4/, LaF/sub 3/, SrF/sub 2/, BaF/sub 2/, KCaF/sub 3/, KY/sub 3/F/sub 10/, Rb/sub 2/NaYF/sub 6/, BaY/sub 2/F/sub 8/, Y/sub 2/SiO/sub 5/, Y/sub 3/Al/sub 5/O/sub 12/, YAlO/sub 3/, LuPO/sub 4/, Ca/sub 5/(PO/sub 4/)/sub 3/F, LiYO/sub 2/, and ScBO/sub 3/. Spectral determinations have been made of the resonant absorption and emission cross sections between 850 and 1100 nm, and the emission decay times of the upper laser level have been measured. The emission cross sections have been evaluated using the absorption cross section and principle of reciprocity, and again using the Fuchtbauer-Ladenberg formula. Agreement between the two methods is within 20% for most materials. The results are discussed in the framework of requirements for an effective diode-pumped Yb/sup 3+/ laser system. Ca/sub 5/(PO/sub 4/)/sub 3/F:Yb is predicted to exhibit the most useful laser properties and is expected to be far superior to Y/sub 3/Al/sub 5/O/sub 12/:Yb in many key microscopic parameter values. >

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...

Laser and spectroscopic properties of Sr 5 (PO 4 ) 3 F:Yb

Sr5(PO4)3F (S-FAP) has been investigated as a new Yb-doped laser crystal belonging to the apatite structural family. The spectroscopy of the Yb3+ ion and the laser properties of the medium have been investigated. The maximum absorption cross section of Yb in S-FAP is 8.6 × 10−20 cm2, and the maximum emission cross section is 7.3 × 10−20 cm2. The measured emission lifetime of Yb3+ is 1.26 ms. An Yb:S-FAP laser has been demonstrated with a Ti:sapphire laser pump operating at 899 nm. The Yb:S-FAP laser was measured to have slope efficiencies as high as 71%. The spectroscopy and laser studies are reported, as well as certain thermal, mechanical, and optical properties.

YTTERBIUM-DOPED APATITE-STRUCTURE CRYSTALS : A NEW CLASS OF LASER MATERIALS

A new class of Yb‐lasers is summarized in this article. The apatite family of crystals, based on the hexagonal structure of the mineral fluorapatite, has been found to impose favorable spectroscopic and laser properties on the Yb3+ activator ion. Crystals of Yb‐doped Ca5(PO4)3F, Sr5(PO4)3F, CaxSr5−x(PO4)3F, and Sr5(VO4)3F have been grown and investigated. Several useful laser crystals have been identified which offer a variety of fundamental laser parameters for designing diode‐pumped systems. In general, this class of materials is characterized by high emission cross sections (3.6–13.1×10−20 cm2), useful emission lifetimes (0.59–1.26 ms), a strong pump band (σabs=2.0–10.0×10−20 cm2), and pump and extraction wavelengths near 900 and 1045 nm, respectively. Efficient lasing has been demonstrated for several of the members of this class of materials, and high optical quality crystals have been grown by the Czochralski method. A summary of the laser parameters and a discussion of the Yb:apatite class of laser...

Laser, optical, and thermomechanical properties of Yb-doped fluorapatite

The laser performance of Yb-doped fluorapatite (Ca/sub 5/(PO/sub 4/)/sub 3/F or FAP), is assessed by employing a Ti:sapphire laser operating at 905 nm as the pump source. We have measured slope efficiencies to be as high as 79%; the residual decrement from the quantum defect-limited efficiency of 87% is accounted for by the presence of passive loss at the 1043-nm laser wavelength. The important spectral properties of Yb:FAP were evaluated, including the absorption and emission cross sections, excited-state lifetime, and ground-state energy-level splitting. The emission and absorption cross sections of Yb/sup +3/ in FAP are found to be substantially larger than those of other Yb-doped media. The thermal, physical, and optical properties of the FAP host are reported as well. >

Vibrational structure in the emission spectra of Yb3+-doped apatite crystals

Abstract We have determined the ground state energy levels of Yb 3+ in crystals with the apatite structure from the low temperature emission spectra of Yb-doped crystals of calcium, strontium and barium fluorophosphates, calcium chlorophosphate and strontium fluorovanadate. Analyses of the data reveal that the previously reported laser transition arises from an electronic level of Yb interacting with the local vibrational modes of the Yb-O bond.

Investigation of the laser properties of Cr/sup 3+/:LiSrGaF/sub 6/

A boule of Cr:LiSGAF (Cr/sup 3+/:LiSrGaF/sub 6/), the Ga analog of Cr:LiSAF, was grown, a laser sample was fabricated, and its efficiency was measured using a laser-pumped laser configuration. The laser performance near 820 nm and related properties of Cr:LiSGAF are reported. The use of Sr instead of Ca results in a red shift of the absorption and emission band (along with an increase in the emission cross section). Insight into the effect of a change in the identity of the substitutional site on the properties of the laser is provided. >

Properties of Cr:LiSrAlF 6 crystals for laser operation

We have performed several physical and optical measurements on the Cr:LiSAF (LiSrAlF(6)) laser material that are relevant to its laser performance, including thermal and mechanical properties, water durabilities, and Auger upconversion constants. The expansion coefficient, Youngs modulus, fracture toughness, thermal conductivity, and heat capacity are all used to determine an overall thermomechanical figure of merit for the crystal. An investigation of the water durability suggests that the cooling solution should be maintained at pH = 7 to ameliorate problems associated with water dissolution. The Auger constant was found to become much more significant at higher Cr doping, in which excited-state migration leads to a substantial increase in the upconversion rate. We propose a design for a 50-W Cr:LiSAF laser system that is based on a detailed knowledge of all the relevant material parameters.

752 nm wing-pumped Cr:LiSrAlF/sub 6/ laser

The authors have demonstrated a LiSrAlF/sub 6/:Cr/sup 3+/ (Cr:LiSrAlF/sub 6/) laser pumped at 752 nm in the longwave wing of the /sup 4/A/sub 2/ to /sup 4/T/sub 2/ pump band. Measured optical, laser, and thermal properties of LiSrAlF/sub 6/-LiSrCrF/sub 6/ solid solutions indicate that efficient laser pumping can be achieved in the 750-780 nm region, and that AlGaAs laser diode arrays may be used to make efficient high-power diode-pumped tunable solid-state lasers. >