175 research outputs found
High power modelocking using a nonlinear mirror
This thesis presents work on the high average power operation of pulsed diode-pumped
solid-state lasers by using a laser configuration known as the bounce geometry.
The bounce geometry has previously produced efficient, high power and
high spatial quality laser outputs in continuous-wave, Q-switched and modelocked
regimes. This thesis explores the capabilities of the bounce geometry for power
scaling, shown using Nd:YVO4 and Nd:GdVO4 in both a passively Q-switched laser
system and a variety of nonlinear mirror modelocked systems.
The high gain experienced by Nd-doped gain media pumped at 808 nm has traditionally
posed difficulties in producing stable passive Q-switching with Cr4+:YAG.
By using a novel stigmatic design of the bounce geometry that experiences lower
gain, but highly circular output, passive Q-switching with > 11 W of average power
is produced, at a pulse repetition rate of 190 kHz. This is the highest output power
ever achieved from a passively Q-switched Nd-doped vanadate laser to date.
Nonlinear mirror modelocking is a passive modelocking technique that employs a
χ(2) nonlinear medium in combination with a dichroic output coupler. The first
nonlinear mirror modelocking of a bounce geometry laser is presented, obtaining
11.3 W of average power and 57 ps pulse duration using a type-II phase-matched
KTP nonlinear crystal. Using type-I phase-matched BiBO, shorter pulses of 5.7 ps
in duration are obtained at an average power of 6.1 W. The nonlinear mirror modelocking
technique is then applied to the stigmatic bounce geometry laser, obtaining
a highly stable train of modelocked pulses with pulse duration 14 ps and an average
power of 12 W, with high spatial quality output.
Mixed vanadate lasers offer customisation of the laser fluorescence spectrum, but
tend to experience lower gain than single vanadates. Using the mixed vanadate
combination Nd:Gd0.6Y0.4YVO4 in the bounce geometry, 27.5 W of average power
in continuous-wave operation is shown. This is the highest power of any mixed
vanadate laser ever reported. By then applying the nonlinear mirror modelocking
technique to the mixed vanadate system, 16.8 W of average modelocked output
power and a pulse duration of 12.7 ps is obtained. This is simultaneously the first
time that the nonlinear mirror technique has been applied to mixed vanadate gain
media and the highest power of any modelocked mixed vanadate laser to date.
Finally, power scaling of a nonlinear mirror modelocked Nd:GdVO4 laser in the
bounce geometry is achieved through use of the double bounce geometry design
and through use of a high power pump diode. The system employing the high
power pumping produced > 30 W of average power — world record power using the
nonlinear mirror technique
Coherent master equation for laser modelocking
Modelocked lasers constitute the fundamental source of optically-coherent ultrashort-pulsed radiation, with huge impact in science and technology. Their modeling largely rests on the master equation (ME) approach introduced in 1975 by Hermann A. Haus. However, that description fails when the medium dynamics is fast and, ultimately, when light-matter quantum coherence is relevant. Here we set a rigorous and general ME framework, the coherent ME (CME), that overcomes both limitations. The CME predicts strong deviations from Haus ME, which we substantiate through an amplitude-modulated semiconductor laser experiment. Accounting for coherent effects, like the Risken-Nummedal-Graham-Haken multimode instability, we envisage the usefulness of the CME for describing self-modelocking and spontaneous frequency comb formation in quantum-cascade and quantum-dot lasers. Furthermore, the CME paves the way for exploiting the rich phenomenology of coherent effects in laser design, which has been hampered so far by the lack of a coherent ME formalism
Optics and Quantum Electronics
Contains table of contents for Section 3, reports on twenty-one research projects and a list of publications and meeting papers.Joint Services Electronics Program Contract DAAL03-92-C-0001U.S. Air Force - Office of Scientific Research Contract F49620-91-C-0091Charles S. Draper Laboratories Contract DL-H-441692MIT Lincoln LaboratoryNational Science Foundation Grant ECS 90-12787Fujitsu LaboratoriesU.S. Navy - Office of Naval Research Grant N00014-92-J-1302National Center for Integrated Photonic TechnologyNational Science Foundation Grant ECS 85-52701U.S. Navy - Office of Naval Research (MFEL) Grant N00014-91-C-0084U.S. Navy - Office of Naval Research (MFEL) Grant N00014-91-J-1956National Institutes of Health Grant R01-GM35459-08U.S. Air Force - Office of Scientific Research Grant F49620-93-1-0301MIT Lincoln Laboratory Contract BX-5098Electric Power Research Institute Contract RP3170-2
Optics and Quantum Electronics
Contains table of contents for Section 3 and reports on twenty-one research projects.Joint Services Electronics Program Contract DAAL03-89-C-0001Joint Services Electronics Program Contract DAAL03-92-C-0001U.S. Air Force - Office of Scientific Research Contract F49620-91-C-0091Charles S. Draper Laboratories Contract DL-H-441629MIT Lincoln LaboratoryCharles S. Draper Laboratories, Inc. Contract DL-H-418478Fujitsu LaboratoriesNational Science Foundation Grant ECS 90-12787National Center for Integrated PhotonicsNational Science Foundation Grant EET 88-15834National Science Foundation Grant ECS 85-52701U.S. Air Force - Office of Scientific Research Contract F49620-88-C-0089U.S. Navy - Office of Naval Research Contract N00014-91-C-0084U.S. Navy - Office of Naval Research Grant N00014-91-J-1956Johnson and Johnson Research GrantNational Institutes of Health Contract 2-R01-GM35459U.S. Department of Energy Grant DE-FG02-89 ER14012-A00
Few-Cycle High Energy Mid-Infrared Pulse From Ho:YLF Laser
Over the past decade, development of high-energy ultrafast laser sources has led to important breakthroughs in attoscience and strong-field physicsstudy in atoms and molecules. Coherent pulse synthesis of few-cycle high-energy laser pulse is a promising tool to generate isolated attosecond pulses via high harmonics generation (HHG). An effective way to extend the HHG cut-off energy to higher values is making use of long mid-infrared (MIR) driver wavelength, as the ponderomotive potential scales quadratically with wavelength. If properly scaled in energy to multi-mJ level and few-cycle duration, such pulses provide a direct path to intriguing attoscience experiments in gases and solids, which even permit the realization of bright coherent table-top HHG sources in the water-window and keV X-ray region. However, the generation of high-intensity long-wavelengthMIR pulses has always remained challenging, in particular starting from high-energy picosecond 2-μm laser driver, that is suitable for further energy scaling of the MIR pulses to multi-mJ energies by utilizing optical parametric amplifiers (OPAs). In this thesis, a front-end source for such MIR OPA is presented. In particular, a novel and robust strong-field few-cycle 2-μm laser driver directly from picosecond Ho:YLF laser and utilizing Kagome fiber based compression is presented. We achieved: a 70-fold compression of 140-μJ, 3.3-ps pulses from Ho:YLF amplifier to 48 fs with 11 μJ energy. The work presented in this thesis demonstrates a straightforward path towards generation of few-cycle MIR pulses and we believe that in the future the ultrafast community will benefit from this enabling technology. The results are summarized in mainly four parts: The first part is focused on the development of a 2-μm, high-energy laser source as the front-end. Comparison of available technology in general and promising gain media at MIR wavelength are discussed. Starting from the basics of an OPA, the design criteria, constraints on the pump & seed source and proper phase-matching conditions requirement for efficient amplification are discussed. In particular, starting from the challenge of developing a Ho:YLF oscillator, pulse amplification and the problem of gain narrowing are addressed. In the second part, various nonlinear compression schemes are discussed in general and specifically, inhibited-coupling Kagome fiber based compression is discussed. The experimental results for the generation of few-cycle, μJ-level 2-μm laser pulses in a two-stage compression scheme are then presented. In the third part, the seed pulse generation for the MIR OPA by utilizing supercontinuum (SC) are presented. The theoretical background of SC generation and the constraints on the pulse duration are discussed. Finally, in the last part, the results obtained are summarized in conclusion and the outlook in presented. The front-end source developed here can be used to generate few-cycle MIR pulses by employing nonoxide based nonlinear crystals. Moreover, as both the pump and seed pulses are derived from the same laser source, it offers the possibility of generating a passively carrier-envelope phase (CEP) stable idler
Generation of terahertz-modulated optical signals using AlGaAs/GaAs laser diodes
The Thesis reports on the research activities carried out under the Semiconductor-Laser Terahertz-Frequency Converters Project at the Department of Electronics and Electrical Engineering, University of Glasgow.
The Thesis presents the work leading to the demonstration of reproducible harmonic modelocked operation from a novel design of monolithic semiconductor laser, comprising a compound cavity formed by a 1-D photonic-bandgap (PBG) mirror. Modelocking was achieved at a harmonic of the fundamental round-trip frequency with pulse repetition rates from 131 GHz up to a record-high frequency of 2.1 THz. The devices were fabricated from GaAs/AlGaAs material emitting at a wavelength of 860 nm and incorporated two gain sections with an etched PBG reflector between them, and a saturable absorber section.
Autocorrelation studies are reported, which allow the device behaviour for different modelocking frequencies, compound cavity ratios, and type and number of intra-cavity reflectors to be analyzed. The highly reflective PBG microstructures are shown to be essential for subharmonic-free modelocking operation of the high-frequency devices. It was also demonstrated that the multi-slot PBG reflector can be replaced with two separate slots with smaller reflectivity.
Some work was also done on the realisation of a dual-wavelength source using a broad-area laser diode in an external grating-loaded cavity. However, the source failed to deliver the spectrally-narrow lines required for optical heterodyning applications. Photomixer devices incorporating a terahertz antenna for optical-to microwave down-conversion were fabricated, however, no down-conversion experiments were attempted. Finally, novel device designs are proposed that exploit the remarkable spectral and modelocking properties of compound-cavity lasers.
The ultrafast laser diodes demonstrated in this Project can be developed for applications in terahertz imaging, medicine, ultrafast optical links and atmospheric sensing
Real-time measurements of dissipative solitons in a mode-locked fiber laser
Dissipative solitons are remarkable localized states of a physical system
that arise from the dynamical balance between nonlinearity, dispersion and
environmental energy exchange. They are the most universal form of soliton that
can exist in nature, and are seen in far-from-equilibrium systems in many
fields including chemistry, biology, and physics. There has been particular
interest in studying their properties in mode-locked lasers producing
ultrashort light pulses, but experiments have been limited by the lack of
convenient measurement techniques able to track the soliton evolution in
real-time. Here, we use dispersive Fourier transform and time lens measurements
to simultaneously measure real-time spectral and temporal evolution of
dissipative solitons in a fiber laser as the turn-on dynamics pass through a
transient unstable regime with complex break-up and collision dynamics before
stabilizing to a regular mode-locked pulse train. Our measurements enable
reconstruction of the soliton amplitude and phase and calculation of the
corresponding complex-valued eigenvalue spectrum to provide further physical
insight. These findings are significant in showing how real-time measurements
can provide new perspectives into the ultrafast transient dynamics of complex
systems.Comment: See also M. Narhi, P. Ryczkowski, C. Billet, G. Genty, J. M. Dudley,
Ultrafast Simultaneous Real Time Spectral and Temporal Measurements of Fibre
Laser Modelocking Dynamics, 2017 Conference on Lasers and Electro-Optics
Europe & European Quantum Electronics Conference, paper EE-3.5 (2017
Femtosecond Cr⁴⁺: forsterite laser for applications in telecommunications and biophotonics
In this thesis, the development of a femtosecond Cr⁴⁺:forsterite solid-state laser is described where the mode-locking procedure was initiated using two novel saturable absorbers. One was a GaInNAs quantum-well device and the other a quantum-dot-based saturable absorber. These devices had not previously been exploited for the generation of femtosecond pulses from a solid-state laser but in the course of this project, successful mode-locked laser operation in the femtosecond domain was demonstrated for both devices.
When the GaInNAs device was incorporated in the Cr⁴⁺:forsterite laser, transform-limited pulses with durations as short as 62fs were obtained. The performance of this femtosecond laser was significantly superior to that for previous quantum-well based saturable absorbers in the 1300nm spectral region. The dynamics of the device were investigated with the aim of refining subsequent devices and to explore the potential to grow future devices for use at longer wavelengths.
At the outset of my research work quantum-dot based saturable absorbers had not be used for the mode locking of solid-state lasers in the femtosecond regime. The work presented in this thesis showed that quantum-dot structures could be exploited very effectively for this purpose. This was initially achieved with the quantum-dot element being inclined at an off-normal incidence within the cavity but experimental assessment together with further development of the device allowed for implementation at normal incidence. Reliable operation of the femtosecond laser was demonstrated very convincingly where transform-limited pulses of 160fs duration were generated.
Having developed practical femtosecond Cr⁴⁺:forsterite lasers, the final part of the project research was directed towards exemplar applications for a laser operating in the 1300nm spectral region. These were biophotonics experiments in which assessments of both deep tissue penetration and two-photon chromosome cutting were undertaken. This work confirmed the suitability of the 1300nm laser radiation for propagation through substantial thicknesses of biological tissue (~15cm). The demonstration of highly localised two-photon cutting of Muntjac deer chromosomes also represented a novel result because single-photon absorption could be avoided effectively and the temporal broadening of the femtosecond pulses in the delivery optics arising from group velocity dispersion around 1300nm was minimal
Optics and Quantum Electronics
Contains table of contents for Section 2 and reports on eleven research projects.Joint Services Electronics Program Contract DAAL03-89-C-0001National Science Foundation Grant EET 87-00474U.S. Air Force - Office of Scientific Research Contract F49620-88-C-0089Charles S. Draper Laboratory Contract DL-H-404179National Center for Integrated PhotonicsNational Science Foundation Grant ECS 87-18417NEC Research InstituteNational Science Foundation Grant ECS 85-52701Medical Free Electron Laser Program Contract N00014-86-K-0117National Institutes of Health Grant 5-RO1-GM35459Lawrence Livermore National Laboratory Contract B048704U.S. Department of Energy Grant DE-FG02-89-ER14012Columbia University Contract P016310
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