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Intra-cavity frequency-doubled Yb: KYW laser using periodically poled Rb-doped KTP with a volume Bragg grating input coupler
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.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
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2014 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 115, no 2, 161-166 p.Article in journal (Refereed) Published
Abstract [en]

An Yb:KYW laser intra-cavity frequency doubled to the green at 514.7 nm using a periodically poled Rb:KTP crystal with an output power exceeding 1 W is presented. Spectral narrowing and locking at the fundamental wavelength has been achieved by using a volume Bragg grating as the input coupler.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2014. Vol. 115, no 2, 161-166 p.
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-121986DOI: 10.1007/s00340-013-5587-yISI: 000334493900003Scopus ID: 2-s2.0-84899966004OAI: oai:DiVA.org:kth-121986DiVA: diva2:619919
Funder
Swedish Research Council
Note

QC 20140516

Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Compact solid-state lasers in the near-infrard and visible spectral range
Open this publication in new window or tab >>Compact solid-state lasers in the near-infrard and visible spectral range
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The subject of this thesis is the exploration of new concepts for compact solid-state lasers in the visible and near-infrared spectral range using new components such as volume Bragg gratings for wavelength stabilisation and wavelength tuning. Also single-walled carbon nanotubes for mode-locking and Q-switching of lasers have been studied.We have developed a new method for the tuning of solid-state lasers by replacing a dielectric mirror with a transversally chirped volume Bragg grating, which allows smooth wavelength tuning without additional elements inside the laser cavity. The result is a more compact laser, since the tuning mechanism and output coupler are incorporated in one component. Another benefit is an increased efficiency, since additional elements inside the cavity will always add to the total loss of the laser. This has been demonstrated for a broadband ytterbium laser around 1 µm and a single-longitudinal-mode Nd:YVO4 laser around 1.06 µm. A volume Bragg grating has also been used to construct an efficient, narrow-linewidth ytterbium fiber laser and the employment of a volume Bragg gratingas the pump mirror of a solid-state laser for frequency-doubling has been investigated. Both lasers represent a practical solution, eliminating the use of additional intracavity elements.

Second-harmonic generation is an efficient way to access the visible spectral range using diode-pumped solid-state lasers. However, these lasers can suffer from large amplitude fluctuations, which has been analyzed in more detail for an optically-pumped semiconductor disk-laser and a volume Bragg grating locked ytterbiumlaser. The control of those amplitude fluctuations is very important, since many applications like fluorescence microscopy require a laser with a constant output power and as little noise as possible.

In addition to this, we have demonstrated, that saturable absorbers based on quan-tum dots and carbon nanotubes can be used to mode-lock compact laser at a wavelength around 1.03 µm. Those lasers have many interesting applications incommunications, clock generation, metrology and life sciences.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xii, 78, xi p.
Series
Trita-FYS, ISSN 0280-316X ; 2013:13
Keyword
volume Bragg gratings, single-longitudinal-mode laser, laser tuning, Q-switching, mode-locking, carbon nanotubes, semiconductor lasers, neodymium, ytterbium, nonlinear optics, KTP
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-121976 (URN)978-91-7501-764-8 (ISBN)
Public defence
2013-05-30, FD5, Albanova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130507

Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2015-03-30Bibliographically approved
2. Thermal properties of volume Bragg gratings and its implications on lasers
Open this publication in new window or tab >>Thermal properties of volume Bragg gratings and its implications on lasers
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis contains the results of research on the spectral control of lasers, specifically, the thermal limitations of volume Bragg gratings (VBGs), employed as laser-cavity end mirrors. The investigations consisted of both experiments and numerical simulations. For the experiments, a diode-pumped Yb:KYW laser with a VBG that had an absorption coefficient of 2.8% cm-1, in the 1 μm spectral region, was constructed. The computer model comprised of a transfer-matrix model and a three-dimensional, finite element model, working together.

The absorption of the reflected laser beam changed the reflecting properties of the VBG, which affected the laser’s stability and other performances. The primary effect was a broadening of the grating spectrum accompanied by decreased diffraction efficiency. The reduced reflectivity lead to a leakage of the radiation through the grating during lasing. Both the experiments and the simulations showed that the laser became successively more unstable when the power was increased. Also, the simulations showed that this increased sensitivity was due to a reshaping of the intensity distribution profile inside the grating, which, in turn, lead to a sharp reduction of the diffraction efficiency. For circulating powers above this limit, the laser output rolled off and the power was instead leaking out through the VBG.

Furthermore, the simulations also showed that the power limit was highly dependent on the length of the employed VBG. For instance, a 2 mm long VBG could withstand approximately 9.5 times higher incident power than a 10 mm long one could. Also, it was found that the limit, expressed in the terms of the incident power, related approximately linearly to the size of the beam radius.

Abstract [sv]

Denna licentiatavhandling innehåller forskningsresultat som behandlar spektral kontroll av lasrar, specifikt genom volymbraggitters (VBG) termiska begränsningar, då de används som speglar i laserkaviteter. Undersökningarna bestod av både experiment och simuleringar. För experimenten konstruerades en diod-pumpad Yb:KYW laser med ett VBG som hade en absorptionskoefficient på 2,8% cm-1, i våglängdsområdet kring en mikrometer.

Datormodellen innefattade en modell av gitterstrukturen baserad på överföringsmatriser och en tredimensionell modell baserad på finita elementmetoden, för beräkning av värme-fördelningen.

Absorption av den reflekterade laserstrålen ändrade volymbraggittrets reflekterande egenskaper, vilket i sin tur påverkade laserns stabilitet och dess prestanda. De huvudsakliga effekterna var en breddning av gittrets spektra och en minskad diffraktionsverkningsgrad. Både experimenten och simuleringarna visade att en laser blir successivt mer instabil när den optiska effekten ökar. Simuleringarna visade även att den ökade känsligheten berodde på en förändring av intensitetsfördelningen inuti gittret, vilket accelererade reduktionen av gittrets reflekterande förmåga. Uttryckt i mot gittret infallande effekt, har lasern en tydlig övre effektgräns. När den gränsen har uppnåtts leder vidare ökning av pumpeffekten i huvudsak till ökat läckage genom volymbraggittret, och inte till ökad uteffekt hos laserstrålen.

Vidare visade simuleringarna också att en lasers effektgräns är starkt beroende av längden på det använda volymbraggittret. Till exempel tålde ett 2 mm långt gitter cirka 9,5 gånger högre infallande effekt än ett 10 mm långt gitter. Dessutom visade det sig att effektgränsen, uttryckt i infallande effekt, berodde approximativt linjärt på strålradiens storlek.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. v, 54 p.
Series
Trita-FYS, ISSN 0280-316X ; 2013:12
Keyword
Thermal effects, Volume Bragg Gratings, VBG, Lasers
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-122004 (URN)978-91-7501-744-0 (ISBN)
Presentation
2013-05-29, FA 32, Albanova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:15 (English)
Opponent
Supervisors
Note

QC 20130507

Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2015-03-30Bibliographically approved
3. Properties of Volume Bragg Gratings and Nonlinear Crystals for Laser Engineering
Open this publication in new window or tab >>Properties of Volume Bragg Gratings and Nonlinear Crystals for Laser Engineering
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on two topics: thermal limitations of volume Bragg gratings (VBGs) employed as laser-cavity mirrors and formation of color centers in KTiOPO4 and its isomorphs.

To explore the mechanisms of the thermal limitations of VBGs in high power lasers, I designed and constructed a diode-pumped, solid‑state laser with a VBG as cavity mirror that had a significantly higher absorption than what is typical. Thereby I could study the limiting thermal effects by using only moderate intra-cavity power. Additionally, I designed a computer model to numerically investigate the thermal effects in VBGs. Both the experiments and the simulations showed that the laser became successively more unstable when the power was increased. Absorption of the reflected laser beam causes broadening of the grating spectrum accompanied by decreasing diffraction efficiency. The reduced reflectivity leads to a leakage of the radiation through the grating. Moreover, the simulations showed that this increased instability was due to a reshaping of the intensity distribution profile inside the grating, which, in turn, leads to a sharp reduction of the diffraction efficiency.

High-intensity visible radiation induces color centers in KTiOPO4, which can lead to severe decrease in the performance of the crystal and can cause catastrophic breakdown. The formation of color centers was investigated by measuring picosecond, blue-light induced infrared absorption (BLIIRA) in periodically-poled KTiOPO4, Rb:KTiOPO4, RbTiOPO4, KTiOAsO4 and RbTiOAsO4 through thermal lens spectroscopy using a common-path interferometer. This setup is capable of measuring absorption as low as 10-5 cm-1. The dependence of the BLIIRA signal on blue light average power and intensity as well as on the crystal temperature was studied. The results show the presence of at least two different types of color centers. A higher level of remnant absorption was observed in the phosphates compared to that of the arsenates. The largest portion of the induced absorption is attributed to photo-generated electrons and holes being self-trapped in the proximity to the Ti4+ and O2- ions, respectively, forming polaron color centers. Stabilization of these centers is aided by the presence of mobile alkali metal vacancies in the crystal.

Abstract [sv]

Denna avhandling fokuserar på både volymbraggitters (VBGs) termiska begränsningar, i tillämpning som speglar i laserkaviteter, och på bildandet av färgcentra i KTiOPO4 och isomorfa kristaller.

För att undersöka de termiska effekterna i VBGer som medför begränsningar på högeffektlasrar utfördes både experiment och simuleringar. För experimenten konstruerades en diod-pumpad Yb:KYW laser med ett VBG som har betydligt högre absorption än vad som är typiskt. Därmed kunde de termiska effekterna studeras vid måttliga intrakavitetseffekter. Simuleringarna bestod av två delmodeller; gitterstrukturen modelerades med överföringsmatriser och värmeflödet med en tredimensionell modell baserad på finita elementmetoden. Både experimenten och simuleringarna visade att en laser blir successivt mer instabil när den optiska effekten ökar. Absorptionen av laserstrålen i VBGt förändrade dess spektrala egenskaper, vilket i sin tur påverkade laserns stabilitet och prestanda. De huvudsakliga effekterna var en breddning av gittrets spektrum med en minskad reflektans. Simuleringarna visade även att den ökade instabiliteten berodde på en förändring av strålningens intensitetsfördelning inuti gittret, vilket accelererade reduktionen av gittrets reflekterande förmåga. I termer av den effekt som faller in mot gittret, har lasern en tydlig övre effektgräns. När den gränsen har uppnåtts leder vidare ökning av pumpeffekten i huvudsak till ökat läckage genom volymbraggittret, i stället för till ökad uteffekt hos laserstrålen.

Kortvågigt synlig ljus av hög intensitet inducerar färgcentra i KTiOPO4, vilket kan leda till kraftigt reducerad transparens och kan orsaka permanent skada i kristallen. För att undersöka skapandet av dessa färgcentra mättes den termiska lins som uppstår vid blå-ljus-inducerad infraröd absorption (Eng: blue-light induced infrared absorption = BLIIRA) inducerad av blåa laserpulser vid en våglängd av 398 nm och vid pulslängder i storlek av pikosekunder i periodiskt‑polad KTiOPO4, Rb:KTiOPO4, RbTiOPO4, KTiOAsO4 och RbTiOAsO4. Den termiska linsen mättes med en metod kallad gemensam-vägsträcka-interferometer (Eng: common-path interferometer), en metod känslig nog för att mäta absorption så låg som 10-5 cm-1. Dessutom undersöktes hur nivån av BLIIRA beror på medeleffekten och intensiteten hos den blåa laserstrålen samt på kristalltemperaturen. Resultaten visar att det bildas minst två typer av färgcentra med olika livslängder. Vidare observerades en högre grad av långsamt avklingande absorption i fosfaterna jämfört med arsenaterna. Den största delen av den inducerade absorptionen tillskrivs fotogenererade elektroner och hål som ”självfångas” i närheten av Ti4+ respektive O2- joner, och bildar färgcentra av polaron karaktär. Stabilisering av dessa centra underlättas av lättrörliga alkalivakanser i kristallerna.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. ix, 86 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2015:69
Keyword
volume Bragg grating, VBG, thermal effects, nonlinear optics, KTiOPO4, quasi-phase matching, photochromic damage, grey-tracking, color centers, blue-light induced infrared absorption, BLIIRA
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-173868 (URN)978-91-7595-697-8 (ISBN)
Public defence
2015-10-12, AlbaNova, FB42, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150922

Available from: 2015-09-22 Created: 2015-09-21 Last updated: 2015-09-22Bibliographically approved

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