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Novel Technologies for Mode-Locking of Solid-State Lasers
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The subject of this thesis is the investigation of novel technologies for mode-locking of diode-pumped, solid-state lasers. Novel saturable absorbers are used: quantum dots (QDs) and carbon nanotubes (CNTs), which both are low-dimensional nano-formations. In addition, mode-locking by cascaded nonlinearities is explored.

Absorber structures containing self-assembled InGaAs QDs are characterised in detail by pump-probe experiments, time-resolved photoluminescence spectroscopy, and measurement of the nonlinear reflectivity. The samples show sub-picosecond relaxation times of the reflectivity, modulation depths between 0.18% and 2.9%, as well as low saturation fluences on the order of 1–10μJ/cm2. The structures’ design parameters are related to their transient and nonlinear performance.

The characterised QD saturable absorbers are then used for mode-locking of diode-pumped, solid-state lasers, delivering picosecond pulses with optical spectra in the region of 1020–1040nm. In particular, a QD absorber with a saturation fluence of 4μJ/cm2 and a relaxation time <200fs is successfully employed for fundamental mode-locking of an Yb:KYW laser at a repetition rate of 1GHz. This laser emits pulses with a duration of 1.7ps at an output power of 339mW. Apart from this, an Yb-thin-disc laser is demonstrated, emitting pulses with a duration of 1.6ps at an output power of 13W, thereby showing, that the absorber withstands fluences of up to 2.4mJ/cm2 without being damaged.

An absorber with a linear loss of only 1% is obtained by embedding CNTs in a thin plastic film, coated onto a glass substrate. Using this absorber, mode-locking of an optically-pumped semiconductor disc-laser is achieved. The laser emits pulses with a duration of 1.12ps at a repetition rate of 613MHz and with an average output power of 136mW.

For cascaded mode-locking, a periodically-poled KTP crystal is placed inside a laser cavity and the two second-order nonlinearities from second-harmonic generation and back-conversion are used to emulate a third-order nonlinearity with an effective nonlinear refractive index of 2.33·10−17m2/W. For precise control of the nonlinearity, the laser’s spectrum is fixed to a wavelength of 1029.1nm by a volume Bragg grating. The laser emits pulses with a duration of 16ps at a repetition rate of 210MHz and with an output power of 690mW.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , xiii, 131 p.
Series
Trita-FYS, ISSN 0280-316X ; 2013:48
Keyword [en]
laser, mode-locked laser, pulsed laser, quantum dot, carbon nanotube, nonlinear optics, saturable absorber, Kerr-lens mode-locking, ultra-fast laser, picosecond laser, pulsed laser, semiconductor saturable absorber
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-131455ISBN: 978-91-7501-840-9 (print)OAI: oai:DiVA.org:kth-131455DiVA: diva2:656442
Public defence
2013-11-05, FA32, AlbaNova Universitetscentrum, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20131016

Available from: 2013-10-16 Created: 2013-10-15 Last updated: 2013-10-16Bibliographically approved
List of papers
1. Semiconductor Quantum-Dot Saturable Absorber Mirrors for Mode-Locking Solid-State Lasers
Open this publication in new window or tab >>Semiconductor Quantum-Dot Saturable Absorber Mirrors for Mode-Locking Solid-State Lasers
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2014 (English)In: The Physics and Engineering of Compact Quantum Dot-based Lasers for Biophotonics / [ed] Edik Rafailov, Berlin: Wiley-VCH Verlagsgesellschaft, 2014, 1, 123-172 p.Chapter in book (Other academic)
Place, publisher, year, edition, pages
Berlin: Wiley-VCH Verlagsgesellschaft, 2014 Edition: 1
Keyword
solid-state lasers, mode-locked ultra-short pulse trains, Cr:forsterite laser, Yb-laser, molecular beam epitaxy, pulse repetition rates, semiconductor, quantum dots, saturable absorbers
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-131452 (URN)2-s2.0-84926397365 (Scopus ID)978-3-527-41184-9 (ISBN)
Note

QC 20131016

Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2013-10-16Bibliographically approved
2. Transient behaviour of quantum-dot saturable absorber mirrors at varying excitation fluence
Open this publication in new window or tab >>Transient behaviour of quantum-dot saturable absorber mirrors at varying excitation fluence
2014 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 116, no 4, 919-927 p.Article in journal (Refereed) Published
Abstract [en]

We present results from studying the carrier dynamics in self-assembled InAs/GaAs quantum-dot saturable absorbers intended for mode-locking of solid-state lasers. Four samples are examined, featuring controlled variations in the resonance condition of the electric field inside the absorber, the number of quantum-dot (QD) layers and the thickness of the GaAs barriers between these QD layers. Pump-probe experiments are conducted at a wide range of excitation fluences and reveal a fast relaxation component of the initial bleaching at low excitation fluences, while a slowly relaxing induced transparency becomes dominant at higher excitation fluences. Time-resolved photoluminescence measurements reveal a large and slowly relaxing induced transparency due to a capture of excess carriers from the barrier bands into the QDs and a slow radiative recombination there. The resonance condition as well as the thickness of the barriers between the QD layers can be used to control the relaxation behaviour. The fastest response is obtained in a structure with an increased number of QD layers at each individual anti-node of the electric field, which is attributed to the appearance of efficient non-radiative recombination channels and capture centres. These centres are probably related to dislocations and other defects appearing in thick QD stacks.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-131454 (URN)10.1007/s00340-014-5778-1 (DOI)000341369600017 ()2-s2.0-84906951488 (Scopus ID)
Note

Updated from submitted to published.

QC 20141009

Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2017-12-06Bibliographically approved
3. Gigahertz repetition rate mode-locked Yb:KYW laser using self-assembled quantum dot saturable absorber
Open this publication in new window or tab >>Gigahertz repetition rate mode-locked Yb:KYW laser using self-assembled quantum dot saturable absorber
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2013 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 110, no 3, 327-333 p.Article in journal (Refereed) Published
Abstract [en]

Fundamental mode-locking is achieved in a 1.036 GHz cavity using a semiconductor quantum dot saturable absorber mirror with a fast relaxation time component of down to 550 fs. The dispersive cavity delivers 1.7 ps wide pulses with spectra supporting sub-picosecond pulse durations and an MA(2) of 1.3. An average output power of up to 339 mW at wavelengths around 1,032 nm is achieved and the saturable absorber's damage threshold is identified as a limitation for further power scaling.

Keyword
Power, Ghz, Microscopy, Locking
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-120538 (URN)10.1007/s00340-013-5375-8 (DOI)000316198700009 ()2-s2.0-8489142439 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 224668Swedish Research Council
Note

QC 20130411

Available from: 2013-04-11 Created: 2013-04-11 Last updated: 2017-12-06Bibliographically approved
4. Carbon nanotube mode-locked optically-pumped semiconductor disk laser
Open this publication in new window or tab >>Carbon nanotube mode-locked optically-pumped semiconductor disk laser
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2013 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 15, 17806-17813 p.Article in journal (Refereed) Published
Abstract [en]

An optically pumped semiconductor disk laser was mode-locked for the first time by employing a single-walled carbon nanotube saturable absorber. Stable passive fundamental mode-locking was obtained at a repetition rate of 613 MHz with a pulse length of 1.23 ps. The mode-locked semiconductor disk laser in a compact geometry delivered a maximum average output power of 136 mW at 1074 nm.

Keyword
Solid-State Lasers, Saturable Absorber, High-Power, Locking, Pulses
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-121987 (URN)10.1364/OE.21.017806 (DOI)000322366300042 ()2-s2.0-84880951935 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130930. Updated from submitted to published.

Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2017-12-06Bibliographically approved
5. Cascaded mode-locking of a spectrally controlled Yb: KYW laser
Open this publication in new window or tab >>Cascaded mode-locking of a spectrally controlled Yb: KYW laser
2014 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 116, no 2, 493-499 p.Article in journal (Refereed) Published
Abstract [en]

Self-starting and stable mode-locking of an Yb:KYW laser in the picoseconds pulse regime has been achieved by exploiting a positive cascaded Kerr lens in periodically poled KTP. The use of a volume Bragg grating (VBG), for locking the output spectrum of the laser, was essential to achieve a stable mode-locked operation in this wide gain bandwidth laser material. The laser emitted stable, nearly transform-limited pulses with a duration of 16 ps, at a repetition rate of 210 MHz, and with an energy of 3.2 nJ. The mode-locked spectrum was centred at 1,029.1 nm and featured a FWHM bandwidth of 85 pm, which was effectively determined by the VBG. Combination of a large cascaded Kerr nonlinearity with spectral limiting by a VBG represents so far the best opportunity for stable mode-locking of a broadband laser to produce near-transform-limited picosecond pulses.

Keyword
Laser accessories, Locks (fasteners), Ytterbium, Broad-band lasers, Kerr nonlinearity, Mode-locked spectra, Periodically poled KTP, Pico-second pulse, Repetition rate, Transform-limited pulse, Volume bragg grating (VBG)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-131453 (URN)10.1007/s00340-013-5725-6 (DOI)000339727000028 ()2-s2.0-84904473166 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20140904

Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2017-12-06Bibliographically approved

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