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Diode-pumped rare-earth-doped quasi-three-level lasers
KTH, School of Engineering Sciences (SCI), Physics.
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.
Series
Trita-FYS, ISSN 0280-316X ; 2005:70
Keyword [en]
Optics, laser optics
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-544ISBN: 91-7178-220-6 (print)OAI: oai:DiVA.org:kth-544DiVA: diva2:14374
Public defence
2005-12-16, Sal FD5, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100901Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2010-09-01Bibliographically approved
List of papers
1. Generation of blue light at 469 nm by efficient frequency doubling of a diode-pumped Nd:YAG laser
Open this publication in new window or tab >>Generation of blue light at 469 nm by efficient frequency doubling of a diode-pumped Nd:YAG laser
2002 (English)In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 38, no 7, 324-325 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Antireflection coatings, Continuous wave lasers, Crystals, Etalons, Laser resonators, Mirrors, Neodymium lasers, Optical fiber coupling, Optical resolving power, Pumping (laser), Second harmonic generation, Stimulated emission, Blue light generation, Dielectric mirrors, Frequency doubling, Laser rod, Semiconductor lasers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8887 (URN)10.1049/el:20020209 (DOI)000174939500017 ()
Note
QC 20100901Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2017-12-14Bibliographically approved
2. Efficient generation of blue light by frequency doubling of a Nd:YAG laser operating on 4F3/2 → 4I9/2 transitions
Open this publication in new window or tab >>Efficient generation of blue light by frequency doubling of a Nd:YAG laser operating on 4F3/2 → 4I9/2 transitions
2003 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 76, no 2, 135-141 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Continuous wave lasers, Energy transfer, Frequency doublers, Pumping (laser), Frequency doubling, Neodymium lasers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8888 (URN)10.1007/s00340-002-1079-1 (DOI)000182170800007 ()
Note
QC 20100901Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2017-12-14Bibliographically approved
3. Modeling of energy-transfer upconversion and thermal effects in end-pumped quasi-three-level lasers
Open this publication in new window or tab >>Modeling of energy-transfer upconversion and thermal effects in end-pumped quasi-three-level lasers
2004 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, 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.

Keyword
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
Identifiers
urn:nbn:se:kth:diva-8889 (URN)10.1364/AO.43.004753 (DOI)000223415700017 ()2-s2.0-4444243195 (Scopus ID)
Note
QC 20100901Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2017-12-14Bibliographically approved
4. Quasi-three-level Nd:YAG laser under diode pumping directly into the emitting level
Open this publication in new window or tab >>Quasi-three-level Nd:YAG laser under diode pumping directly into the emitting level
2006 (English)In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 261, no 1, 109-113 p.Article in journal (Refereed) Published
Abstract [en]

We present theoretical and experimental investigations on ground-state direct pumping at 869 nm into the emitting level F-4(3/2) of end-pumped quasi-three-level Nd:YAG lasers operating at 946 nm. We have demonstrated, what we believe is for the first time, a Nd:YAG laser at 946 nm directly pumped by diodes and obtained 1.6 W of output power.

Keyword
Diode-pumped solid-state lasers, Direct pumping, Quasi-three-level lasers, Diodes, Electron transitions, Ground state, Optical communication, Optical pumping, Solid state lasers, Diode-pumped solid-state lasers, Direct pumping, Emitting level, Nd:YAG laser, Quasi-three-level lasers, Neodymium lasers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8890 (URN)10.1016/j.optcom.2005.11.058 (DOI)000236864000019 ()2-s2.0-33645846916 (Scopus ID)
Note
QC 20100901. Uppdaterad från Submitted till Published 20100901.Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2017-12-14Bibliographically approved
5. Polymer encapsulated miniature Nd:YAG lasers
Open this publication in new window or tab >>Polymer encapsulated miniature Nd:YAG lasers
Show others...
2003 (English)In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 39, no 20, 1446-1448 p.Article in journal (Refereed) Published
Abstract [en]

A continuation of the previously introduced microstructured silicon carrier concept for diode-pumped solid-state lasers is presented, using novel heat-conducting polymers as a carrier. The most prominent features of the silicon carrier concept are maintained, adding to the mass production possibilities of the inexpensive polymers. The first experiments, using a continuous wave Nd:YAG microchip laser, have given an output power of 2 W at 1064 nm, showing the potential of this new approach.

Keyword
Conductive plastics, Encapsulation, Heat conduction, Microstructure, Microchip lasers, Neodymium lasers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8891 (URN)10.1049/el:20030924 (DOI)000186031500014 ()
Note
QC 20100901Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2017-12-14Bibliographically approved
6. High power Q-switched Nd:YAG laser mounted in a silicon microbench
Open this publication in new window or tab >>High power Q-switched Nd:YAG laser mounted in a silicon microbench
Show others...
2004 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 36, no 5, 383-385 p.Article in journal (Refereed) Published
Abstract [en]

A high-power Q-switched Nd:YAG/Cr:YAG laser mounted in a silicon microbench is presented. It reaches an average output power well above 2 W and the pulse width is in the order of 1.4 ns. The use of microstructure silicon carriers provides efficient thermal control, compact integration and alignment of active and passive optical components.

Keyword
Lasers diode-pumped, Microstructure fabrication, Q-switched, Charge coupled devices, Doping (additives), Laser pulses, Micromachining, Microstructure, Neodymium lasers, Photolithography, Pumping (laser), Scanning electron microscopy, Silicon, Laser diode pumped, Microstructure fabrication, Q switched lasers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8892 (URN)10.1016/j.optlastec.2003.10.011 (DOI)000221202600007 ()
Note
QC 20100901Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2017-12-14Bibliographically approved
7. Laser performance and thermal lensing in high-power diode pumped Yb:KGW with athermal orientation
Open this publication in new window or tab >>Laser performance and thermal lensing in high-power diode pumped Yb:KGW with athermal orientation
2006 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 83, no 1, 55-59 p.Article in journal (Refereed) Published
Abstract [en]

A comparative, experimental study of the high-power diode-pumped laser performance and thermal lensing properties between standard b-cut Yb:KGW and Yb:KGW cut along an athermal direction is presented. The results show that thermal lens properties in both the b-cut and the athermal direction-cut crystals are determined by anisotropic thermal expansion in Yb:KGW. Thermal gradients due to the pump beam cause thermal lensing even in the athermal direction-cut geometry. The thermal lens is much weaker and less astigmatic in the athermal direction-cut crystal, for the same absorbed power. These properties allow generation of better-quality laser beams with the athermal direction-cut crystal as compared to the b-cut crystal.

Keyword
Anisotropy, Laser applications, Oxidation, Pumping (laser), Laser performance, Thermal lensing, Semiconductor lasers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7829 (URN)10.1007/s00340-005-2115-8 (DOI)000235746900011 ()2-s2.0-33644663574 (Scopus ID)
Note
QC 20100714Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2017-12-14Bibliographically approved
8. Fluorescence dynamics and rate equations analysis in Er3+,Yb3+ doped double tungstates
Open this publication in new window or tab >>Fluorescence dynamics and rate equations analysis in Er3+,Yb3+ doped double tungstates
Show others...
2006 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 45, no 19, 4715-4725 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Continuous-wave lasers; Doping concentrations; Fluorescence dynamics; Rate equation analysis; Concentration (process); Equations of state of solids; Erbium compounds; Semiconductor doping; Solid state lasers; Tungsten compounds; Ytterbium compounds
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-5454 (URN)10.1364/AO.45.004715 (DOI)000238665900028 ()2-s2.0-33746174995 (Scopus ID)
Note
QC 20100713. Uppdaterad från Accepted till Published 20100713.Available from: 2006-03-13 Created: 2006-03-13 Last updated: 2017-11-21Bibliographically approved

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