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Passive Q-switching at 1.54 µm of an Er-Yb:GdCa4O(BO3)3 laser with a Co2+:MgAl2O4 saturable absorber
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0002-2508-391X
KTH, School of Engineering Sciences (SCI), Physics.ORCID iD: 0000-0001-7688-1367
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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.

Place, publisher, year, edition, pages
2005. Vol. 81, no 1, 49-52 p.
Keyword [en]
Crystalline materials; Erbium; Gadolinium compounds; Magnesium compounds; Q switching; Thermal conductivity; Ytterbium
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-5453DOI: 10.1007/s00340-005-1832-3ISI: 000230033800010Scopus ID: 2-s2.0-21044449285OAI: oai:DiVA.org:kth-5453DiVA: diva2:9823
Note
QC 20100713Available from: 2006-03-13 Created: 2006-03-13 Last updated: 2017-11-21Bibliographically approved
In thesis
1. Novel materials for Yb and Er-Yb doped microchip lasers
Open this publication in new window or tab >>Novel materials for Yb and Er-Yb doped microchip lasers
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The objective of this thesis has been to investigate novel host material configurations for high-power end-pumped Er-Yb co-doped, or Yb doped microchip lasers and try to increase their performance. In Er-Yb co-doped systems, the main limitation is the thermal shortcomings of the phosphate glass host material. The thesis presents some novel results that contribute to the search for a crystalline replacement. In Yb doped systems, most end-pumped schemes reported have been using relatively low-power single-emitter diodes. The thesis presents experiments with Yb:KGW microchips end-pumped by high-power diode bars. Another common limitation of end-pumped Yb microchip lasers is the thermal lens that destabilizes the cavity and decreases the beam quality. The approach to reduce the thermal lens by using an athermal propagation direction has been evaluated and the results are presented in the thesis.

In the search for a crystalline host material for Er-Yb systems, borates have been found increasingly interesting. Consequently, we started out by investigating Gadolinium-calcium-oxoborate, GdCOB, which could be grown in platinum crucibles. It was found that the cw performance of such monolithic microchips is quite comparable to glass hosts in terms of slope efficiency, but the threshold is significantly larger. As for Q-switched performance, which is essential to most Er-Yb applications, the first efficient Q-switched results with a crystalline host is presented in the thesis. Similar to the cw regime, the slope efficiencies are comparable to glass, while the threshold is quite high. However, the perhaps most important parameter, maximum output power before thermal fracture, is neither significantly improved nor worsened compared with phosphate glass. This is believed to be due to higher threshold and a stronger thermal expansion that negates the benefit of a thermal conductivity that is only 2-3 times higher. To find a host material that could withstand higher pump powers, we turned our attention to the double-tungstates KGW and KYW, which have higher thermal conductivity and higher cross-sections. They have, however, energy level lifetimes which differ significantly from glass or borates and as a consequence, a thorough spectroscopic investigation has been undertaken to optimize dopant concentrations. Laser experiments on crystals with dopant concentrations based on this investigation are expected in the near future.

When pumping Yb:KGW with a high-power diode bar, we achieved output powers of 9 – 12.4 W under different experimental conditions with incident powers of 18.3 – 26 W. The incident power of 26 W in one design was enough to fracture the crystal. Using a crystal cut for propagation along an athermal direction and comparing it with an identical b-cut crystal, we found that the thermal lens in the athermally oriented crystal was about a factor two weaker at the same absorbed power.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. vii, 56 p.
Series
Trita-FYS, ISSN 0280-316X ; 2006:19
Keyword
mid-IR lasers, laser materials
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-3874 (URN)91-7178-299-0 (ISBN)
Presentation
2006-03-31, FA31, AlbaNova, Roslagstullsbacken 21, STOCKHOLM, 13:00
Opponent
Supervisors
Note
QC 20101116Available from: 2006-03-13 Created: 2006-03-13 Last updated: 2010-11-16Bibliographically approved
2. On diode-pumped solid-state lasers
Open this publication in new window or tab >>On diode-pumped solid-state lasers
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
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:nbn:se:kth:diva-4580 (URN)978-91-7178-841-2 (ISBN)
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

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Pasiskevicius, ValdasLaurell, Fredrik

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