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On diode-pumped solid-state lasers
KTH, School of Engineering Sciences (SCI), Applied Physics.
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The research that is presented in this thesis can be divided into two major parts. The first part concerns longitudinally pumped, bulk Er-Yb lasers. In these lasers, the main limitation is the thermal shortcomings of the phosphate glass host material. From the laser experiments and the spectroscopic measurements on crystalline host materials, as well as an investigation to bring further light to the physical background of the involved dynamics, the thesis presents some novel results that contribute to the search for a crystalline replacement. The second part concerns novel laser concepts applied to Yb-doped double tungstate lasers. Different crystal orientations are investigated, such as an athermal orientation for reduced thermal lensing and a conical refraction orientation for complete polarization tuning. Furthermore, the introduction of volume Bragg gratings in the cavity enables wide spectral tuning ranges and extremely low quantum defects.

Regarding the first part, the main results are the achievement of 15 % slope efficiency in a monolithic, continuous-wave Yb:GdCOB laser and the achievement of Q-switching of the same laser. The Q-switched pulse durations were around 5-6 ns and the Q-switched slope efficiency was 11.6 %. For both lasers, a maximum output power of 90 mW was obtained, which is close to ordinary glass lasers under similar conditions. A spectroscopic investigation into the Er,Yb-codoped double tungstates was also performed and the results have enabled mathematical modeling of the fluorescence dynamics in these materials. Finally, the temperature dependence of the dynamics in Er,Yb:YAG was studied and the results have given some insight into the physical background of the mechanisms involved.

Regarding the second part, different end-pumped Yb:KReW laser cavities were constructed to demonstrate the different concepts. With a laser crystal cut for propagation along the athermal direction at 17º angle clockwise from the dielectric direction Nm, the thermal lens could be reduced by 50 %. In these experiments the maximum output power was 4 W at 60 % slope efficiency. In another cavity incorporating a volume Bragg grating in a retroreflector set-up, the wavelength could be continuously tuned between 997 - 1050 nm. The spectral bandwidth was 10 GHz and the peak output power was 3 W. The same output power could also be obtained at 1063 nm with the grating positioned as an output coupler instead. If, on the other hand, the grating was positioned as an input coupler, 3.6 W output power at 998 nm was obtained at a quantum defect of only 1.6 %. Furthermore, using a crystal oriented for propagation along an optic axis, internal conical refraction could be used to establish arbitrary control of the polarization direction as well as the extinction ratio. Even unpolarized light could be enforced despite the highly anisotropic medium. With this configuration, the maximum output power was 8.6 W at 60 % slope efficiency which equals the performance of a reference crystal with standard orientation. The completely novel concepts of laser tuning with Bragg grating retroreflectors, of low quantum defect through Bragg grating input couplers and of polarization tuning by internal conical refraction can all easily be applied to several other laser materials as well.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , 76 p.
Series
Trita-FYS, ISSN 0280-316X ; 2007:81
Keyword [en]
near-infrared lasers, end-pumped lasers, Q-switching, erbium, ytterbium, GdCOB, KGW, KYW, Co:MALO, laser materials, thermal lensing, end-pumping, spectroscopy, conical refraction, volume Bragg gratings, holographic gratings, laser tuning
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4580ISBN: 978-91-7178-841-2 (print)OAI: oai:DiVA.org:kth-4580DiVA: diva2:12971
Public defence
2008-01-18, FA32, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100713Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2010-07-14Bibliographically approved
List of papers
1. Luminescent and laser properties of Yb-Er:GdCa4O(BO3)3: a new crystal for eye-safe 1.5-µm lasers
Open this publication in new window or tab >>Luminescent and laser properties of Yb-Er:GdCa4O(BO3)3: a new crystal for eye-safe 1.5-µm lasers
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2004 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 79, no 5, 577-581 p.Article in journal (Refereed) Published
Abstract [en]

We present for the first time 1.5-μm laser emission in Yb-Er:GdCa 4O(BO3)3 (GdCOB). The crystals were grown by the Czochralski method from platinum crucibles. Spectroscopic and laser tests of the crystals are described. A continuous-wave output power of 80 mW was achieved in a monolithic microchip cavity under laser-diode pumping.

Keyword
Continuous wave lasers; Crystalline materials; Energy transfer; Luminescence; Optical pumping; Optical radar; Phonons; Quantum optics; Relaxation processes; Semiconductor lasers; Thermal conductivity; Ytterbium compounds
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7823 (URN)10.1007/s00340-004-1605-4 (DOI)000224130100010 ()2-s2.0-5544283497 (Scopus ID)
Note
QC 20100713 QC 20110923Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2015-03-30Bibliographically approved
2. Passive Q-switching at 1.54 µm of an Er-Yb:GdCa4O(BO3)3 laser with a Co2+:MgAl2O4 saturable absorber
Open this publication in new window or tab >>Passive Q-switching at 1.54 µm of an Er-Yb:GdCa4O(BO3)3 laser with a Co2+:MgAl2O4 saturable absorber
Show others...
2005 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 81, no 1, 49-52 p.Article in journal (Refereed) Published
Abstract [en]

We report, for the first time to our knowledge, efficient passive Q-switching of the 1.54-μm laser transition in an Er-Yb-doped crystalline medium. The laser configuration is a compact microchip design that is suitable for a range of practical applications such as range finding and lidar. The slope efficiency of 11.6%, pulse duration of 5-6 ns and average output power of 88 mW are all comparable with standard Er-Yb:glass lasers.

Keyword
Crystalline materials; Erbium; Gadolinium compounds; Magnesium compounds; Q switching; Thermal conductivity; Ytterbium
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-5453 (URN)10.1007/s00340-005-1832-3 (DOI)000230033800010 ()2-s2.0-21044449285 (Scopus ID)
Note
QC 20100713Available from: 2006-03-13 Created: 2006-03-13 Last updated: 2017-11-21Bibliographically approved
3. Polarization-tunable Yb:KGW laser based on internal conical refraction
Open this publication in new window or tab >>Polarization-tunable Yb:KGW laser based on internal conical refraction
Show others...
2007 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 19, 2783-2785 p.Article in journal (Refereed) Published
Abstract [en]

Using internal conical refraction, we demonstrate an Yb:KGW laser where the polarization state can be arbitrarily altered without any additional cavity components. The extinction ratio can also be altered between 1:1 and 40:1. The maximum output power achieved was 8.6 W at a slope efficiency of 60.5% with respect to incident pump power. This equals the power performance of a standard Yb:KGW laser used for reference.

Keyword
Laser beam effects; Light extinction; Light polarization; Refraction; Ytterbium compounds; Extinction ratio; Polarization state; Slope efficiency; Semiconductor lasers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7825 (URN)10.1364/OL.32.002783 (DOI)000250499900006 ()2-s2.0-39749139758 (Scopus ID)
Note

QC 20100713

Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2016-12-14Bibliographically approved
4. 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
5. Yb3+,Er3+:YAG at high temperatures: energy transfer and spectroscopic properties
Open this publication in new window or tab >>Yb3+,Er3+:YAG at high temperatures: energy transfer and spectroscopic properties
Show others...
2007 (English)In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 271, no 1, 142-147 p.Article in journal (Refereed) Published
Abstract [en]

Energy transfer and spectroscopic properties at high temperatures have been investigated in Er,Yb:YAG crystals. It is shown that at elevated temperatures around 600-800 degrees C these characteristics become similar to those in the efficient 1.5 mu m laser medium - Er,Yb-doped phosphate glasses. (c) 2006 Elsevier B.V. All rights reserved.

Keyword
Energy transfer; Fiber optics; Glass; Lasers; Spectroscopic analysis; Elevated temperatures; Yb-doped phosphate glasses; Crystals
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7827 (URN)10.1016/j.optcom.2006.09.046 (DOI)000243984800024 ()2-s2.0-33846043655 (Scopus ID)
Note
QC 20100714Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2015-03-30Bibliographically approved
6. Efficient Yb: KGW lasers end-pumped by high-power diode bars
Open this publication in new window or tab >>Efficient Yb: KGW lasers end-pumped by high-power diode bars
Show others...
2006 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 82, no 2, 235-239 p.Article in journal (Refereed) Published
Abstract [en]

The laser performance of Yb:KGW under end-pumping with high-power diode bars has been investigated. In one configuration, the pump is delivered through an optical fiber yielding a symmetric but unpolarized pump spot. In the second configuration, the pump is delivered through an optical lens system yielding a polarized but asymmetric pump spot. Both configurations resulted in a maximum optical to optical efficiency of 47% and a maximum power of 12.4 W has been generated with the fiber coupled pump source. The output power was limited by crystal fracture, which occurred at an estimated temperature gradient of 1.2 x 10(5) K/m. Thermal lensing and laser tuning characteristics are also investigated.

Keyword
Crystal structure; Laser tuning; Light polarization; Optical fibers; Optical instrument lenses; Optical pumping; Semiconductor diodes; Temperature control; High-power diode bars; Optical efficiency; Thermal lensing; Unpolarized pump spot; Semiconductor lasers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-5455 (URN)10.1007/s00340-006-2171-8 (DOI)000236750700013 ()2-s2.0-33645711196 (Scopus ID)
Note

QC 20100714. Uppdaterad från Accepted till Published 20100714.

Available from: 2006-03-13 Created: 2006-03-13 Last updated: 2017-11-21Bibliographically 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: 2012-03-14Bibliographically approved
8. Finite beams in reflective volume Bragg gratings: theory and experiments
Open this publication in new window or tab >>Finite beams in reflective volume Bragg gratings: theory and experiments
2008 (English)In: IEEE Journal of Quantum Electronics, ISSN 0018-9197, Vol. 44, no 1, 81-89 p.Article in journal (Refereed) Published
Abstract [en]

We present a theoretical model to describe finite beams incident on reflective volume Bragg gratings. We also give experimental results that verify our model. From these results, we identify certain properties of reflective volume Bragg gratings, such as beam waist, incidence angle and beam profile, that have direct impact on the design of laser cavities that include such gratings. We also show how these gratings can act as spatial mode filters.

Keyword
Holographic gratings; Laser beam distortion; Spatial filters
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8198 (URN)10.1109/JQE.2007.910448 (DOI)000252720600010 ()2-s2.0-43249091205 (Scopus ID)
Note
QC 20100714Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2015-03-30Bibliographically approved
9. Widely tunable Yb:KYW laser with a volume Bragg grating
Open this publication in new window or tab >>Widely tunable Yb:KYW laser with a volume Bragg grating
2007 (English)In: Optics Express, ISSN 1094-4087, Vol. 15, no 3, 1003-1010 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate a narrowband, continuously tunable Yb: KYW laser locked by a volume Bragg grating at oblique incidence in a retroreflector configuration. The tuning range was 997 nm to 1050 nm (15 THz) with bandwidth < 0.1 nm and a maximum output power of 4.7 W. In a high- quality beam with M-2 < 1.3, the maximum output power was 1.7 W. We also demonstrate 3 W output power at 1064 nm from the same Yb: KYW laser with the grating at normal incidence.

Keyword
Bandwidth; Fiber Bragg gratings; Laser beams; Laser mode locking; Laser tuning; Ytterbium; Output power; Retroreflectors; Volume Bragg grating; Yb:KYW lasers; Solid state lasers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8204 (URN)10.1364/OE.15.001003 (DOI)000244682200029 ()2-s2.0-33846863604 (Scopus ID)
Note
QC 20100714Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2015-03-30Bibliographically approved
10. Tunable Yb:KYW laser using volume Bragg grating in s-polarization
Open this publication in new window or tab >>Tunable Yb:KYW laser using volume Bragg grating in s-polarization
2008 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 91, no 1, 85-88 p.Article in journal (Refereed) Published
Abstract [en]

We report on a volume-Bragg-grating tunable Yb:KYW laser. By using s-polarized light on the grating, we obtain an output power of 3 W in a single beam, doubled compared to earlier p-polarization results. The laser tunability was from 996 nm to 1048 nm. Detailed measurements of the laser spectrum revealed a bandwidth of 10 GHz.

Keyword
Bandwidth; Laser beams; Laser tuning; Light polarization; Laser spectrum; Bragg gratings
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8205 (URN)10.1007/s00340-008-2937-2 (DOI)000254247100017 ()2-s2.0-43249100263 (Scopus ID)
Note
QC 20100714Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2015-03-30Bibliographically approved
11. Quasi-two-level Yb:KYW laser with a volume Bragg grating
Open this publication in new window or tab >>Quasi-two-level Yb:KYW laser with a volume Bragg grating
2007 (English)In: Optics Express, ISSN 1094-4087, Vol. 15, no 21, 13930-13935 p.Article in journal (Refereed) Published
Abstract [en]

Using a volume Bragg grating as input coupler, we demonstrate an Yb:KYW laser with a very small quantum defect (1.6%) and an output power of 3.6 W. The laser was longitudinally diode-pumped at 982 nm and the laser wavelength was determined by the grating to 998 nm, with a laser bandwidth of 10 GHz (33 pm). Due to the low quantum defect, the laser should be readily scalable to 20 W or more without critical thermal effects.

Keyword
Bandwidth; Bragg gratings; Laser radiation; Quantum theory; Thermal effects; Wavelength; Critical thermal effects; Input couplers; Quantum defect; Volume Bragg grating; Waveguide couplers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8202 (URN)10.1364/OE.15.013930 (DOI)000251223100050 ()2-s2.0-35348949596 (Scopus ID)
Note
QC 20100714Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2015-03-30Bibliographically approved

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