| 1. |
- Bjurshagen, Stefan, et al.
(författare)
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946-nm Nd : YAG laser under ground-state direct diode-pumping at 869 nm
- 2005
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Ingår i: 2005 Conference on Lasers & Electro-Optics (CLEO), Vols 1-3. - WASHINGTON, DC : OPTICAL SOC AMERICA. - 1557527954 ; , s. 328-330
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Konferensbidrag (refereegranskat)abstract
- We have demonstrated, what we believe is for the first time, direct diode-pumping at 869 rim into the emitting level of a quasi-three-level Nd:YAG laser operating at 946 nm.
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| 2. |
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| 3. |
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| 4. |
- Bjurshagen, Stefan, et al.
(författare)
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Crystal growth, spectroscopic characterization, and eye-safe laser operation of erbium- And ytterbium-codoped KLu(WO4)2
- 2008
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Ingår i: Applied Optics. - 1559-128X. ; 47:5, s. 656-665
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Tidskriftsartikel (refereegranskat)abstract
- Erbium (Er)- and Ytterbium (Yb)-codoped monoclinic KLu(WO4) 2 single crystals were grown by top seeded solution growth-slow cooling method for several different doping concentrations. Growth parameters have been optimized to obtain macrodefect-free single crystals. Er energy levels involved in the 4I13/2 → 4I 15/2 were determined by 6 K polarized optical absorption. The maximum emission cross section for this electronic transition has been evaluated, being 2.85 × 10-20 cm2 for E||Nm at 1535 nm. Laser oscillation in the 1.5 μm range was obtained by pumping the Yb ion at 980 nm and sensitizing Er. The maximum output power achieved was 152 mW, with 1.2% slope efficiency.
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| 5. |
- Bjurshagen, Stefan
(författare)
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Diode-pumped Nd : YAG lasers for generation of blue light by frequency doubling
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quasi-three-level lasers in neodymium-doped crystals such asNd:YAG, Nd:YLF and Nd:YVO4have received a great deal of interest becausethey allow generation of blue light by frequency doubling. Forsolid-state blue laser sources, there exist numerousapplications as in high-density optical data storage, colourdisplays, submarine communication and biologicalapplications. Efficient lasing on quasi-three-level transitions at 900-950nm in Nd-doped crystals is considerably more difficult toachieve than on the stronger four-level transitions at 1-1.1µm. The problems with these quasi-three-level transitionsare a significant reabsorption loss at room temperature and avery small stimulated emission cross section. This requires atight focusing of the pump light, which is achieved byend-pumping with high-intensity diode lasers. n this thesis, progress in diode-pumped solid-state lasersfor generation of blue light by frequency doubling has beenmade. Nd:YAG lasers at the 946 nm transition have been builtand a maximum power of 7.0 W was obtained. By inserting a thinquartz etalon in the laser cavity, the938.5 nm laser linecould be selected. An output power of 3.9 W was obtained. By using nonlinear crystals, frequency-doubling of laserlight at both 946 nm and 938.5 nm by second harmonic generation(SHG) was achieved. SHG of the 946 nm transition gives bluelight at 473 nm. Efficient generation of blue light has beenachieved in periodically poled KTP, both in single-passextra-cavity and intracavity configurations. More than 0.5 Wwas obtained at 473 nm by intracavity doubling. Intracavity SHGof the 938.5 nm transition gave slightly more than 200 mW at469 nm. The influence of energy-transfer upconversion (ETU) is adetrimental effect in Nd-doped lasers. An analytical model hasbeen developed for continuous wave quasi-three-level lasersincluding the influence of ETU. The results of the generaloutput modelling are applied to a laser with Gaussian beams,and rigorous numerical calculations have been done to study theinfluence of ETU on threshold, output power, spatialdistribution of population-inversion density and fractionalthermal loading. The model is applied to a laser operating at946 nm in Nd:YAG, where thermal lensing and the dependency oflaser-beam size are investigated in particular. A simple modelfor the degradation of laser beam quality from a transversallyvarying saturated gain is also proposed, which is in very goodagreement with measurements of the laser in a plane-planecavity.
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| 6. |
- Bjurshagen, Stefan, 1975-
(författare)
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Diode-pumped rare-earth-doped quasi-three-level lasers
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Bjurshagen, Stefan, et al.
(författare)
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Efficient generation of blue light by frequency doubling of a Nd:YAG laser operating on 4F3/2 → 4I9/2 transitions
- 2003
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Ingår i: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 76:2, s. 135-141
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Tidskriftsartikel (refereegranskat)abstract
- Efficient room-temperature operation of F-4(3/2) --> I-4(9/2) transitions in diode-end-pumped Nd:YAG lasers at 946 nm and 938.5 nm is reported. 7.0-W continuous-wave output power at 946 nm and 3.9 W at 93 8.5 nm have been obtained. An analytical model has been developed for the quasi-three-level laser including the influence of energy-transfer upconversion. Frequency doubling of these transitions in periodically poled KTP generated blue light at 473 nm and 469 nm. Both single-pass extra-cavity as well as intracavity schemes have been investigated.
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| 8. |
- Bjurshagen, Stefan, et al.
(författare)
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Fluorescence dynamics and rate equations analysis in Er3+,Yb3+ doped double tungstates
- 2006
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 45:19, s. 4715-4725
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Tidskriftsartikel (refereegranskat)abstract
- The fluorescence dynamics in Er3+ and Yb3+ doped KGd(WO4)(2) and KY(WO4)(2) has been investigated. Lifetimes have been measured for the Yb(F-2(5/2)), Er(I-4(13/2)), and Er(S-4(3/2)) levels around 1, 1.5, and 0.55 mu m, respectively. The Yb(F-2(5/2)) lifetimes show a decreasing trend toward the limiting Er(I-4(11/2)) lifetime with increasing Er-to-Yb concentration ratio, whereas the Er(I-4(13/2)) lifetimes are mostly unaffected by the doping concentrations. A rate equation analysis has been performed to explain the observed behavior and gain is calculated for a continuous-wave laser at 1.53 mu m to find the optimum doping concentrations for high gain.
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| 9. |
- Bjurshagen, Stefan, et al.
(författare)
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Generation of blue light at 469 nm by efficient frequency doubling of a diode-pumped Nd:YAG laser
- 2002
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 0013-5194 .- 1350-911X. ; 38:7, s. 324-325
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Tidskriftsartikel (refereegranskat)abstract
- Efficient operation of a diode-pumped Nd: YAG laser at 938.5 nm is reported. A continuous wave output power of 3.9 W is obtained. Single-pass frequency doubling in periodically poled KTP delivered a power of 88 mW at 469 nm. By intracavity frequency doubling an output of 200 mW in the blue region is achieved.
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| 10. |
- Bjurshagen, Stefan, et al.
(författare)
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Modeling of energy-transfer upconversion and thermal effects in end-pumped quasi-three-level lasers
- 2004
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 43:24, s. 4735-4767
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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