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Modeling of energy-transfer upconversion and thermal effects in end-pumped quasi-three-level lasers
KTH, Superseded Departments, Physics.
Acreo AB, Kista.
2004 (English)In: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 43, no 24, 4735-4767 p.Article in journal (Refereed) Published
Abstract [en]

An analytical model of cw quasi-three-level lasers that includes the influence of energy-transfer upconversion (ETU) has been developed. The results of the general output modeling were applied to a laser with Gaussian beams, and rigorous numerical calculations have been made to study the influence of ETU on threshold, output power, spatial distribution of population-inversion density, and fractional thermal loading. The model was applied to a laser operating at 946 nm in Nd:YAG, where the dependence of laser-beam size on laser performance was investigated in particular. A simple model for the degradation of laser-beam quality from a transversally varying saturated gain is proposed that is in good agreement with measurements of the laser in a plane-plane cavity.

Place, publisher, year, edition, pages
2004. Vol. 43, no 24, 4735-4767 p.
Keyword [en]
Color displays, Reabsoprtion losses, Underwater communication, Upconversion effects, Degradation, Energy transfer, Laser beams, Mathematical models, Optical data storage, Parameter estimation, Pumping (laser), Relaxation processes, Lasers
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-8889DOI: 10.1364/AO.43.004753ISI: 000223415700017ScopusID: 2-s2.0-4444243195OAI: diva2:14368
QC 20100901Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2011-09-23Bibliographically approved
In thesis
1. Diode-pumped rare-earth-doped quasi-three-level lasers
Open this publication in new window or tab >>Diode-pumped rare-earth-doped quasi-three-level lasers
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Many rare-earth-doped materials are suitable for laser operation and this thesis focuses on diode-pumped solid-state lasers employing crystals doped with the trivalent rare-earth ions neodymium (Nd3+), ytterbium (Yb3+) and erbium (Er3+). Especially, the quasi-three-level transitions in Nd and Yb have been studied as well as the eye-safe three-level transition around 1.5 µm in Er.

Quasi-three-level laser transitions in neodymium-doped crystals such as Nd:YAG, Nd:YLF and Nd:YVO4 have received a great deal of interest because they allow for generation of blue light by frequency doubling. For solid-state blue laser sources, there exist numerous applications as in high-density optical data storage, colour displays, submarine communication and biological applications.

Efficient lasing on quasi-three-level transitions at 900¬–950 nm in Nd-doped crystals is considerably more difficult to achieve than on the stronger four-level transitions at 1–1.1 µm. The problems with these quasi-three-level transitions are a significant reabsorption loss at room temperature and a small stimulated emission cross section. This requires a tight focusing of the pump light, which is achieved by end-pumping with high-intensity diode lasers. Nd:YAG lasers at the 946 nm transition have been built and a maximum power of 7.0 W was obtained. By inserting a thin quartz etalon in the laser cavity, the 938.5 nm laser line could be selected and an output power of 3.9 W was then obtained.

By using nonlinear crystals, frequency-doubling of laser light at both 946 nm and 938.5 nm was achieved. Efficient generation of blue light at 473 nm has been obtained in periodically poled KTP, both in single-pass extra-cavity and intracavity configurations. More than 0.5 W was obtained at 473 nm by intracavity doubling. Intracavity second harmonic generation of the 938.5 nm transition gave slightly more than 200 mW at 469 nm.

During recent years, Yb-doped double-tungstate crystals like KGW and KYW have shown efficient laser operation. A comparative, experimental study of the laser performance and thermal-lensing properties between standard b-cut Yb:KGW and Yb:KGW cut along a novel athermal direction is presented. The results show that the thermal lens is about two times weaker and less astigmatic in the athermal-direction-cut crystal, for the same absorbed power. Also, Er-Yb-doped KGW and KYW have been investigated and the fluorescence dynamics have been measured for the Yb (2F5/2), Er (4I13/2) and Er (4S3/2) levels around 1 µm, 1.5 µm and 0.55 µm, respectively.

The influence of upconversion is a detrimental effect both in Nd-doped and Er-Yb-doped lasers. Analytical models starting from rate equations have been developed for these lasers including the influence of upconversion effects. The results of the general models have been applied to 946 nm Nd:YAG lasers and to Er-Yb-doped double-tungstate crystals in order to find the optimum doping concentrations for high gain for an eye-safe laser at 1.53 µm.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. viii, 86 p.
Trita-FYS, ISSN 0280-316X ; 2005:70
Optics, laser optics
National Category
Physical Sciences
urn:nbn:se:kth:diva-544 (URN)91-7178-220-6 (ISBN)
Public defence
2005-12-16, Sal FD5, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
QC 20100901Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2010-09-01Bibliographically approved

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