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Spectral control of lasers and optical parametric oscillators with volume Bragg gratings
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [sv]

I den här avhandlingen visas hur lasrar och optiska parametriska oscillatorer (OPO:er) kan styras spektralt med hjälp av volymbraggitter.

Volymbraggitter utgörs av ett periodiskt varierande brytningsindex som skrivits i ett fototermorefraktivt glas. Gittret reflekterar därmed en specifik våglängd som bestäms av perioden hos modulationen, och kan tillverkas med smal bandbredd och hög reflektans beroende på modulationens längd och styrka.

En teoretisk modell har utvecklats för reflektiva volymbraggitters egenskaper om den infallande strålen har en större vinkelspridning än gittrets vinkeltolerans. Detta kan bl.a. inträffa i en laserkavitet där gittret används vid snett infall, och en teoretisk beskrivning är därför ett viktigt redskap för att kunna designa sådana lasrar.

Spektral kontroll av ett antal fasta tillståndslasrar med hjälp av volymbraggitter har i försök påvisats, och lasern har därvid både kunnat avstämmas spektralt samtidigt som en avsmalnad spektral bandbredd erhållits. Lasern kan göras väldigt enkel genom att byta ut en av kavitetsspeglarna mot gittret. Tack vare gittrets goda spektrala urvalsmekanism kan lasern låsas var som helst i förstärkningsspektrumet. De tekniker och lasrar som demonstrerats experimentellt är följande:

Lasring i en enda longitudinell mod erhölls både för en diodpumpad ErYb:glas-laser vid 1553 nm med ca 10 mW:s effekt och 90 kHz linjebredd samt för en diodpumpad Nd:GdVO4-laser vid 1066 nm med 0.85 W:s effekt. Lasrarnas våglängd kunde avstämmas över större delen av gittrets bandbredd på ca. 30 GHz. Genom att bygga Nd:GdVO4-lasern med en monolitisk kavitet kunde även en spektralt synnerligen stabil laser erhållas med under 40 MHz bandbredd. Tillämpningar för dessa lasrar finns både inom spektroskopi samt som källor för intrakavitetsfördubbling till synliga våglängder.

Genom att använda gittret som inkopplingsspegel går det även att framställa lasrar med en väldigt låg kvantdefekt, som därför får minskad värmeutveckling i lasermediet. Detta medger i sin tur att lasrar med höga medeleffekter kan konstrueras, som kan användas bl.a. för olika former av materialbearbetning. I detta arbete har lasrar med låg kvantdefekt byggts med Yb:KYW som laserkristall; både en laser vid 998 nm på 3.6 W som diodpumpades vid 982 nm och med en bandbredd på 10 GHz, samt en laser vid 990 nm på 70 mW som pumpades av en Ti:safir-laser vid 980 nm.

Om volymbraggittret används vid snett infall kan den reflekterade våglängden avstämmas genom att gittret roteras. Denna princip användes i en diodpumpad Yb:KYW-laser till att erhålla en brett avstämbar laservåglängd mellan 996 nm och 1048 nm med en maximal effekt på 3 W och med 10 GHz bandbredd. Genom att placera gittret i en retroreflektor kunde avstämningen göras utan att kaviteten behövde linjeras om. En laser som denna kan exempelvis användas för olika typer av materialkarakterisering och spektroskopi.

Med optiska parametriska oscillatorer (OPO:er) kan laserljus omvandlas till nya våglängder. Därmed kan OPO:er användas som koherenta ljuskällor där inga effektiva lasrar existerar. OPO-processen kan göras effektiv om en pulsad pump används, och den genererade våglängden kan enkelt styras med hjälp av periodiskt polade (PP) icke-linjära kristaller, såsom PP-KTiOPO4, som användes i detta arbete. En nackdel med OPO:er är att i allmänhet är den genererade signalen tämligen spektralt bredbandig. Signalens bandbredd kan dock avsmalnas betydligt om ett spektralt filter såsom ett volymbraggitter används. Genom att byta ut en av speglarna i OPO-kaviteten mot gittret kan utformningen av OPO:n göras väldigt enkel.

I en OPO med en signalvåglängd på 975 nm kunde en avsmalning av bandbredden till 50 GHz påvisas med hjälp av ett braggitter. Detta motsvarar 20 gångers minskning jämfört med om en konventionell spegel används. Som mest erhölls en pulsenergi på 0.34 mJ i signalen. Genom att rotera gittret kunde våglängden avstämmas 21 THz. För att förenkla avstämningen konstruerades även en OPO med gittret i en retroreflektor, samtidigt som kaviteten var av ringtyp. I denna OPO vid en våglängd på 760 nm och med en pulsenergi i signalen på upp till 0.42 mJ erhölls en bandbredd på 130 GHz och ett avstämningsområde på 2.6 THz. Slutligen har en OPO vid 1 µm konstruerats med ett gitter med en transversellt varierande period, s.k. chirp. Därigenom kan våglängden avstämmas väldigt enkelt genom att bara flytta gittret transversellt.

En tillämpning av dessa OPO:er är såsom ljuskällor i olika typer av laserbaserade sensorer, i vilka en specifik och stabil våglängd erfordras. Dessutom kan de smalbandiga OPO:erna användas som första steg i ickelinjära processer i flera steg. Smal bandbredd är då viktig för effektiviteten i den påföljande ickelinjära omvandlingen i nästa steg.

Abstract [en]

The object of this thesis is to explore the usage of reflective volume Bragg gratings in photo-thermo-refractive glass for spectral control of solid-state lasers and optical parametric oscillators, to build tunable and narrowband coherent light-sources.

In order to provide a design tool for use of reflective volume Bragg gratings in laser cavities, a theory was developed that describes the performance of the gratings if the incident beam has finite width with an angular spectrum that is comparable to the grating's angular acceptance bandwidth.

Spectral control was demonstrated in a number of cw solid-state lasers, in terms of narrow bandwidth and tunable wavelength, by use of a volume Bragg grating. The design could be made very simple by replacing one of the cavity mirrors with the grating. Thanks to the grating's strong spectral selectivity, the lasers could be locked anywhere in the gain spectrum, while the laser bandwidth was substantially narrowed. In particular, the following lasers were demonstrated: Single-longitudinal-mode lasing in ErYb:glass at 1553 nm with 90 kHz linewidth and in Nd:GdVO4 at 1066 nm with a linewidth below 40 MHz. Very low quantum defect in Yb:KYW lasers, diode-pumped at 982 nm and lasing at 998 nm with 10 GHz bandwidth, as well as Ti:sapphire-pumped at 980 nm and lasing at 990 nm. An Yb:KYW laser that was widely tunable from 996 nm to 1048 nm with 10 GHz bandwidth.

In nanosecond pulsed optical parametric oscillators (OPOs) based on periodically poled KTiOPO4, narrowband operation and a tunable wavelength were demonstrated with a volume Bragg grating as a cavity mirror. At a signal wavelength of 975 nm, the bandwidth was 50 GHz, a reduction by 20 times compared to using a conventional mirror. A tuning range of 21 THz was also demonstrated. In another OPO at a signal wavelength of 760 nm, a ring-cavity design was demonstrated to provide convenient tuning. A tuning range of 2.6 THz and a bandwidth of 130 GHz was shown. Also, narrowband operation and tuning in an OPO around 1 µm was demonstrated by use of a transversely chirped Bragg grating.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , xiv, 95 p.
Series
Trita-FYS, ISSN 0280-316X ; 2008:13
Keyword [en]
volume Bragg gratings, single-longitudinal-mode laser, laser tuning, erbium, neodymium, ytterbium, nonlinear optics, optical parametric oscillator, KTP, tunable optical parametric oscillator, narrowband optical parametric oscillator
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4691ISBN: 978-91-7178-914-3 (print)OAI: oai:DiVA.org:kth-4691DiVA: diva2:13465
Public defence
2008-04-25, FB53, Albanova, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100813Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2010-08-13Bibliographically approved
List of papers
1. 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
2. Tunable single-longitudinal-mode ErYb:glass laser locked by a bulk glass Bragg grating
Open this publication in new window or tab >>Tunable single-longitudinal-mode ErYb:glass laser locked by a bulk glass Bragg grating
2006 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 11, 1663-1665 p.Article in journal (Refereed) Published
Abstract [en]

A single-longitudinal-mode Er-Yb:glass laser with a linewidth of 90 kHz is demonstrated by locking the laser wavelength to 1552.6 nm with a bulk glass Bragg grating. Using a piezoelectric actuator, the wavelength could be tuned over a range of 0.25 nm (31 GHz) in steps of 17 pro (2.1 GHz), with an output power of a few milliwatts.

Keyword
Actuators; Fiber Bragg gratings; Glass; Laser mode locking; Optical materials; Piezoelectric devices; Glass Bragg grating; Glass lasers; Piezoelectric actuators
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8199 (URN)10.1364/OL.31.001663 (DOI)000237728200025 ()2-s2.0-33745738980 (Scopus ID)
Note
QC 20100813Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2015-03-30Bibliographically approved
3. Single-longitudinal-mode Nd-laser with a Bragg-grating Fabry-Perot cavity
Open this publication in new window or tab >>Single-longitudinal-mode Nd-laser with a Bragg-grating Fabry-Perot cavity
2006 (English)In: Optics Express, ISSN 1094-4087, Vol. 14, no 20, 9284-9292 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate 0.85 W of power in a single longitudinal mode at 1066 nm from a Nd: GdVO4 laser. The laser consists of only two components, the gain medium and a volume Bragg grating in glass, in a simple linear cavity comprising a combination of a Fabry-Perot cavity and a narrowband filter. Thanks to the narrowband Bragg grating, the single longitudinal mode is maintained for a cavity length up to 8 mm, while a continuous tuning of 25 GHz is achieved for a shorter cavity and lower power.

Keyword
Glass; Laser applications; Neodymium; Optical filters; Bragg gratings; Fabry-Perot cavity; Narrowband filters
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8200 (URN)10.1364/OE.14.009284 (DOI)000240981000041 ()2-s2.0-33749415976 (Scopus ID)
Note
QC 20100813. Erratum publicerat i Opt. Express, 15, 9387 (2007).Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2015-03-30Bibliographically approved
4. Monolithic Bragg-locked Nd:GdVO4 laser
Open this publication in new window or tab >>Monolithic Bragg-locked Nd:GdVO4 laser
2007 (English)In: Optics Express, ISSN 1094-4087, Vol. 15, no 18, 11589-11594 p.Article in journal (Refereed) Published
Abstract [en]

We present a monolithic single-longitudinal-mode laser based on Nd:GdVO4 and a volume Bragg grating. The laser at 1066 nm had a bandwidth below 40 MHz at a power of 30 mW. With temperature, the laser frequency could be continuously tuned without mode hops over a range of 80 GHz. The demonstrated laser design is very compact and simple and can be used to lock the laser wavelength anywhere in the gain spectrum.

Keyword
Bandwidth; Frequency modulation; Gain measurement; Monolithic integrated circuits; Spectrum analysis; Laser wavelength; Monolithic single-longitudinal-mode laser
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8201 (URN)10.1364/OE.15.011589 (DOI)000249339800057 ()2-s2.0-34548459852 (Scopus ID)
Note
QC 20100813Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2015-03-30Bibliographically approved
5. 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
6. Experimental and theoretical investigation of a volume-Bragg-grating-locked Yb:KYW laser at selected wavelengths
Open this publication in new window or tab >>Experimental and theoretical investigation of a volume-Bragg-grating-locked Yb:KYW laser at selected wavelengths
2008 (English)In: Optics Express, ISSN 1094-4087, Vol. 16, no 9, 6443-6454 p.Article in journal (Refereed) Published
Abstract [en]

Laser action is demonstrated in Yb:KYW at wavelengths of 990 nm, 997 nm and 1066 nm, when pumped at 980 nm by a Ti: sapphire laser, with a lowest laser quantum defect of 1.0%. The laser output powers at the various wavelengths were 70mW, 160mW and 140mW, respectively. Locking of the laser wavelength and the spectrally close spacing of pump and laser were achieved by the use of a volume Bragg grating as an input coupler. A theoretical model is also presented that accurately describes the laser at various wavelengths, by solving the laser rate equations at spatial points throughout the laser crystal.

Keyword
TUNABLE YB; KY(WO4)(2); CAVITY; GLASS
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8203 (URN)10.1364/OE.16.006443 (DOI)000255663000052 ()2-s2.0-43049127223 (Scopus ID)
Note
QC 20100813. Uppdaterad från submitted till published (20100813).Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2010-08-13Bibliographically approved
7. 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
8. 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
9. Narrowband bulk Bragg grating optical parametric oscillator
Open this publication in new window or tab >>Narrowband bulk Bragg grating optical parametric oscillator
2005 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 17, 2281-2283 p.Article in journal (Refereed) Published
Abstract [en]

A narrowband, pulsed optical parametric oscillator (OPO) whose output coupler is a bulk glass Bragg grating is demonstrated. The OPO is based on periodically poled KTiOPO4 and is pumped by a pulsed, frequency-doubled Nd:YAG laser at 532 nm, generating a signal at 975 nm with a total efficiency of 35%. This novel and compact device shows a spectral bandwidth of 0.16 nm (50 GHz), a decrease by a factor of 20 compared with that when a conventional mirror is used. By using a folded cavity, we demonstrate tunable radiation with a tuning range of 60 nm and maintained spectral bandwidth.

Keyword
Bandwidth; Mirrors; Radiation; Spectrum analysis; Bragg grating; Optical parametric oscillators (OPO); Spectral bandwidth; Tuning range
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8206 (URN)10.1364/OL.30.002281 (DOI)000231436900031 ()2-s2.0-25144518343 (Scopus ID)
Note
QC 20100813Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2015-03-30Bibliographically approved
10. Narrowband and tunable ring optical parametric oscillator with a volume Bragg grating
Open this publication in new window or tab >>Narrowband and tunable ring optical parametric oscillator with a volume Bragg grating
2007 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 22, 3278-3280 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate a tunable nanosecond optical parametric oscillator with a narrowed signal spectrum. This was done by use of a volume Bragg grating based retrorefiector, which makes the tuning simple and yields a compact design. Using periodically poled KTiOPO4 as the nonlinear medium, we generated 0.42 mJ of signal energy at 760 nm with a tuning range of 5 nm (2.6 THz) and a bandwidth of 0.25nm (130 GHz) when the oscillator was pumped at 532 nm with 1.3 mJ of energy.

Keyword
Bandwidth; Bragg gratings; Signal analysis; Spectrum analysis; Signal spectrum; Tunable ring optical parametric oscillators
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8207 (URN)10.1364/OL.32.003278 (DOI)000251747600018 ()2-s2.0-40149094085 (Scopus ID)
Note
QC 20100813Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2015-03-30Bibliographically approved

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