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(a) Extract from pulse train measurement and (b) frequency spectrum obtained by the FFT of the complete time signal. The limited bandwidth of the measurement setup results in overshoots for the time signal and a signal drop at 16 GHz as well as a decreased intensity of the higher harmonics above ∼ 10 GHz in the frequency spectrum.
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We report on passive mode locking of a semiconductor disk laser emitting pulses shorter than 250 fs at 664 nm with a repetition frequency of 836 MHz. A fast saturable absorber mirror fabricated by metal-organic vapor-phase epitaxy in a near-resonant design was used to enable the mode locking operation. It includes two GaInP quantum wells located cl...
Citations
... As a compromise, a home-built mode-locked laser has also been used in [8,9]. A similar approach in the red spectral range was always limited by the performance of the home-built modelocked laser which either shows more than one pulse per round-trip within a picosecond envelope [10,11] or indications of multi-pulse emission [12]. Only lately a stable fundamental mode-locked VECSEL was shown in the red-spectral range [13], enabling the usage of mode-locked emission for applications. ...
... However, high values of dispersion could be introduced through the wedged intracavity diamond, depending on the strength of the Fabry-Perot effect. The oblique incidence of the intracavity beam on the wedged and ar-coated diamond heatspreader allows a reduction of the Fabry-Perot effect such that it is not visible in the autocorrelation in Fig. 2(c), where side-pulses with a separation around 10 ps would appear [10] that go along with a considerable Fabry-Perot modulation of the optical spectrum. Other VECSELs [19,20] with intracavity diamond heatspreader can also show a large time-bandwidth product despite a single pulse per round-trip, so that the diamond could still contribute residual group delay dispersion. ...
Mode-locked vertical external-cavity semiconductor lasers (VECSELs) are a wavelength-versatile laser that relies on a semiconductor saturable absorber mirror (SESAM) to initiate pulsed emission while simultaneously significantly influencing the pulse’s properties. A SESAM can be characterized using a nonlinear reflectivity setup, realized here in the red spectral range around 660 nm and achieving a moderate peak-to-peak variation of 0.17%. We use our home-built mode-locked VECSEL to reach a high maximum fluence up to 430 µJ/cm² with strongly chirped 7.5 ps pulses. This allows the first-of-its-kind characterization of GaInP quantum well SESAMs, thereby revealing saturation fluences of 38 µJ/cm² and 34 µJ/cm² with modulation depths of 5% and 10.3% for SESAMs comprising one or two active quantum wells, respectively. For all structures, a nonsaturable loss of 2.8% is found and attributed to scattering loss.
... Around the quantum system additional barrier and cladding layers are used -also consisting of semiconductor materials. They compensate strain induced by the quantum system and ensure an increased charge carrier confinement [131,132]. At the top, the SESAM is terminated by a cover layer that prevents oxidation and other pollution of the semiconductor surface. ...
... In QW based systems, a modification of the saturation fluence requires more work. A change can be accomplished by the use of multiple QWs [132] but this adds additional layers to the system and might even force a re-design of the whole structure in order to keep the anti-resonant design. ...
Nanostructures like subwavelength metal nanoparticles or quantum dots build the bridge between the atomic length scale and the macroscopic one. Although they consist of thousands of atoms, they show properties only explainable by quantum mechanical approaches. Nowadays, those systems are widely used in commercially available technologies but are still object of scientific research, even down to the clarification of fundamental physical questions. The formation of strongly coupled systems, formed by two or more nanostructures, sources for entangled photons and the nonlinear response of nanosystems are topics of worldwide research in the field of nanooptics. Especially the later offers many open questions and often it is not clear, if restrictions like, e.g., symmetry restrictions from the macroscopic scale still hold in the nanoscopic universe. We address some of those open questions in this thesis experimentally as well as theoretically. The use of ultrafast pump-probe techniques allow us to reveal temporal dynamics on the femto second timescale, while spectroscopic measurements complete the picture. For theoretical modeling, we combine intuitive analytical models with numerical approaches like optimization algorithms and the Finite Element Method. Our research ranges from isolated gold nanoparticles over complex waveguide-like nanocircuits to layered semiconductor structures with embedded quantum dots. The first two chapters lay a basis of physical framework for the later investigated topics. The field of plasmonics is embedded in the theory of electromagnetism and we give an insight in the field of nonlinear optics. Moreover, we introduce computational electrodynamics with a focus on the Finite Element Method and nanostructures that are of interest in the subsequent work. The following two chapters focus on second-harmonic generation on the nanoscale. We demonstrate theoretically and experimentally, that the current understanding has to be expanded. In contrast to the past understanding, subwavelength particles made of a symmetric material do not necessarily have to possess a geometrical asymmetry to emit second-harmonic light. In fact, it is already sufficient if an optical or plasmonic mode of appropriate symmetry is present. We prove our hypothesis in a complex plasmonic nanocircuit, carefully exclude influences that could weaken our statement and, moreover, explore the nonlinear operation of the nanocircuit to its full extend. The later is described by an intuitive analytical model. The next chapter marks the transition towards time resolved experimental techniques. We investigate the temporal dynamics of a low density, quantum dot based semiconductor saturable absorber mirror. We reveal time constants of the recovery process after saturation and determine characteristic constants of the saturation process itself, offering enough information for a future application as mode locking device in an ultrafast red emitting vertical-external-cavity surface emitting laser. Moreover, we also conduct experiments with varying wavelength, that reveal the structure's behavior in spectral proximity to the desired operation wavelength. The last chapter of the thesis focuses again on plasmonic nanostructures but lays focus on the temporal dynamics of quasi free, hot electrons and their role in nonlinear optical processes. Up to now, this relation, as well as the connection to the bandstructure of the material itself, remains rather unclear. We present our experimental approach, involving a multi-color pump-probe setup. We create hot electrons in the conduction band with a 400nm pump pulse, probe the structure with a delayed infrared probe pulse and investigate the impact on the nonlinear signals. Namely, second-harmonic generation, third-harmonic generation and multi-photon luminescence. We observe partly differing changes in all three of them regarding the sign of the modulation as well as recovery and decay times. In the subsequent measurements, we sacrifice the spectral information for a better signal-to-noise ratio by a Lock-In detection scheme with a single photon counting device. Therefor, we focused on the dominating signal, given by changes in the photo luminescence. We investigate excitation power dependent changes in the pump-probe peak and present first steps towards a theoretical model involving a two-temperature model for the thermalization of the generated hot electrons. Moreover, we present a technique for ultrafast multi-color pulse characterization. We use difference-frequency generation in order to obtain cross-correlation frequency resolved optical gating traces from nonlinear micro crystals and also gold nanorods themselves in the sample plane of the experiment.
... While this trend has been remarkably well addressed for continuous-wave operation [2], the work with mode-locked VECSELs has mainly concentrated on the ∼1-μm spectral window [3], where both gain mirror and semiconductor saturable absorber mirror (SESAM) technologies take advantage of the mature InGaAs/GaAs material system. Development of mode-locked VECSELs at other wavelengths has mainly probed the potential of new SESAM material systems for wavelengths ranging from ∼670 nm [4,5] to ∼2 μm [6], without subsequent refined work concerning power scaling or pulse shortening. This is because pushing the frontiers of specific operation parameters at new wavelengths would require the availability of mature technology for both gain mirrors and SESAMs technology, which is not the case when departing from the 1 μm wavelength range. ...
Mode locking of a 1.34 μm vertical external cavity surface emitting laser is demonstrated using a GaSb-based semiconductor saturable absorber mirror (SESAM). The SESAM includes six AlGaSb quantum wells (QWs) with an absorption edge at ∼ 1.37 μm . The proposed approach has two key benefits: the QWs can be grown lattice matched, and only a small number of Bragg reflector layers is required to provide high reflectivity. Pump–probe measurements also reveal that the AlGaSb/GaSb structure exhibits an intrinsically fast absorption recovery on a picosecond timescale. The mode-locked laser pulse train had a fundamental repetition rate of 1.03 GHz, a pulse duration of ∼ 5 ps , and a peak power of ∼ 1.67 W . The demonstration paves the way for exploiting GaSb-based SESAMs for mode locking in the 1.3–2 μm wavelength range, which is not sufficiently addressed by GaAs and InP material systems.
... However, less attention has been paid to nonlinear optical response and photonics devices designed through spin-orbit splitting of 3d electrons in the visible region. Recently, MoS 2 and semiconductor saturable absorber mirror (SESAM) based on well-designed GaInP quantum wells have been used in passive mode locking as the optical modulators in the visible range by using its electron interband transition processes [21][22][23]. Besides, NiO was employed as a mode-locker at the wavelengths of 1065.45 and 1343.12 nm by electron intraband transition arising from ground state ( 3 A 2g ) to excited state ( 3 T 2g ) [20]. ...
... Associated with the higher modulation depth and lower saturation fluence, NiO nanosheet film is reliable in the field of nanophotonics, e.g., optical switching, beam shaping, etc [32,33]. Meanwhile, NiO nanosheet saturable absorber has the advantages in the easy preparation and low cost compared with MoS 2 [21] and SESAM [22,23] that were employed as mode-lockers in the visible region. For ultrafast photonics applications, the mode-locking performance is related to the modulation depth and saturation fluence of the semiconductor saturable absorbers. ...
NiO, a 3d transition-metal oxide with the strong electron correlation, has attracted great physical attention due to the spin-orbit splitting of 3d electrons. By taking advantage of electron transition process originated from 3d spin-orbit splitting, it may be applied to many photonics areas by linear or nonlinear optical response. To further broaden the photonics applications of NiO, we originally explore the nonlinear optical response, saturable absorption, during the electronic transition due to 3d spin-orbit splitting under a strong optical field and successfully applied in the ultrafast photonics as a mode-locker for the generation of visible laser pulses, which is the result of dynamic balancing process by the electron transition arising from ground state (³A2g) to excited state (¹Eg) of spin-orbit splitting in the Ni²⁺ 3d configurations. With the NiO nanosheet film for saturable absorption, we experimentally realize a pulsed visible laser at a wavelength of 640.3 nm for the first time to our knowledge. These results indicate that the study of electron transition process generated by 3d spin-orbit splitting in 3d transition-metal oxides should be helpful for the development of ultrafast photonics and related devices design.
... In this article, we present the design and the comprehensive characterization of a self-mode-locked AlGaInP-based SDL with emission in the red spectral range, where until now, only SESAM mode-locking of VECSELs has been reported. [19][20][21][22] The gain structure is fabricated by metal-organic vaporphase epitaxy in a close coupled showerhead reactor and includes a distributed Bragg reflector with 55 AlAs/ Al 0.5 GaAs pairs. The active region contains 20 compressively strained GaInP QWs embedded in Al 0.33 GaInP barriers and Al 0.55 GaInP cladding layers. ...
We report the mode-locked operation of an AlGaInP-based semiconductor disk laser without a saturable absorber. The active region containing 20 GaInP quantum wells is used in a linear cavity with a curved outcoupling mirror. The gain chip is optically pumped by a 532 nm laser, and mode-locking is achieved by carefully adjusting the pump spot size. For a pump power of 6.8 W, an average output power of up to 30 mW is reached at a laser wavelength of 666 nm. The pulsed emission is characterized using a fast oscilloscope and a spectrum analyzer, demonstrating stable single-pulse operation at a repetition rate of 3.5 GHz. Intensity autocorrelation measurements reveal a FWHM pulse duration of 22 ps with an additional coherence peak on top, indicating noise-like pulses. The frequency spectrum, as well as the Gaussian beam profile and the measured beam propagation factor below 1.1, shows no influence of higher order transverse modes contributing to the mode-locked operation.
... Furthermore, the operating wavelength of a mode-locked VECSEL can be broadly adjusted by changing the material system of the gain and absorber medium. To date, the operating wavelengths reported with a mode-locked VECSEL range from 665 [5] to 1960 nm [6], while the best performance in terms of power and pulse duration has been demonstrated between 960 and 1080 nm [7,8], where the semiconductor media benefit from the maturity and advantages of GaAs-based materials. The shortest pulse duration was recently demonstrated near 1033 nm, with a 107 fs pulse compressed to 96 fs at a repetition rate of 1.63 GHz and with 100 mW of output power [7]. ...
The passive mode locking of vertical external cavity surface emitting lasers (VECSELs) enables the generation of high brightness ultrashort pulses at high repetition rates with unmatched performance. The peak power achievable with sub-200-fs pulse duration is mostly limited by the stability of the fundamental mode-locking regime as side pulses or harmonic mode locking emerges at high pump power. Here, we study a colliding pulse mode-locked VECSEL generating a pulse duration as short as 128 fs, with an average power of 90 mW per beam and a repetition rate of 3.27 GHz. The relevant laser parameters under different pumping regimes before and after the emergence of a side pulse are then used as input parameters for the simulation of the pulse interactions in the saturable absorber. We present a new comprehensive model for the calculation of saturable losses in the saturable absorber mirror and we study the energy transfer between the two counter-propagating pulses. This study reveals how a colliding pulse scheme reduces the saturation fluence of the absorber by a factor 2.9 and suppresses the mode competition between the two counterpropagating pulses of the ring cavity.
... In the past few years, passively SAs of visible regions were primarily centralized on crystals (e.g. Cr 4+ : YAG, Cr 4+ -doped Y 3 Al 5 O 12 ) or semiconductor saturable absorber mirrors (SESAMs) [15][16][17][18][19]. However, SESAMs require expensive fabrication, and crystals are unsuitable for fiber lasers because of the bulky structure. ...
A copper-nanowire (CuNWs)-based saturable absorber (SA) is utilized as a new Q-switcher for pulsed operations in visible regions. The plasmon resonance effect of CuNWs contributes to inducing the saturable absorption property. By incorporating the CuNWs-based SA into a red praseodymium Pr
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>
-doped ZBLAN fiber laser cavity, the red light shifts from a continuous wave (CW) state to a stable pulsed operation state. When it changes the injected pump power, the pulse repetition rate can be varied from 239.8 to 312.4 kHz. The narrowest pulse duration of this laser is 394 ns. Moreover, the maximum output power under a Q-switching operation is 9.6 mW. The results indicate that a CuNWs-based SA is an available Q-switcher for the red laser, revealing the potential of metal nanomaterials for short-pulse generation in visible regions.
... However, one could notice that there already exits several kinds of SAs working at the spectral ranges [38][39][40][41][42], including the transition-metal-doped crystals, the semiconductorsaturable-absorber-mirrors (SESAMs), and so on. For example, Kannari et al. have reported on the use of Cr 4+ : YAG [38] and Cr 4+ -doped Y 3 Al 5 O 12 [39] in pulsed praseodymium (Pr 3+ )-doped YLF 4 lasers, respectively. ...
In this paper, a compact passively Q-switched praseodymium (Pr³⁺)-doped fiber laser at the wavelength of 635 nm with black phosphorus (BP) saturable absorber (SA) was first investigated. BP nanoflakes were manufactured by the liquid-phase-exfoliation method and then embedded into polyvinyl-alcohol (PVA) film for the experimental usage and a fiber pigtail mirror (FPM, by coating dielectric film onto the fiber-end face) was applied to realize a compact Pr³⁺-doped red fiber laser. By transferring a block of the BP-PVA thin film onto the FPM and then incorporating into the compact Pr³⁺-doped fiber laser, the Q-switched operation at 635 nm was achieved. The pulse-repetition rate of the visible-wavelength Q-switched fiber laser can be widely tuned from 108.8 to 409.8 kHz and the shortest pulse duration of this laser is 383 ns. These results reveal that the BP is an available SA for red-light lasers.
... Bek et al. 62 7 InP QD layers 655 nm 1.0 ps 1 mW 852 MHz Bek et al. 63 20 GaInP SCQWs a 665 nm 250 fs 0.5 mW 836 MHz Ranta et al. 64 20 Ga . 46 In .54 ...
The performance of ultrafast semiconductor disk lasers has rapidly advanced in recent decades. The strong interest from industry for inexpensive, compact, and reliable ultrafast laser sources in the picosecond and femtosecond domains has driven this technology toward commercial products. Frequency metrology and biomedical applications would benefit from sub-200-femtosecond pulse durations with peak powers in the kilowatt range. The aim of this review is to briefly describe the market potential and give an overview of the current status of mode-locked semiconductor disk lasers. Particular focus is placed on the ongoing efforts to achieve shorter pulses with higher peak powers.
... 11 Besides these design guidelines, SESAM parameters can be controlled in an even wider range by using quantum dots instead of quantum wells, since these allow an independent control of saturation fluence and modulation depth. 12 In the visible spectrum, red-emitting SESAM mode-locked VECSELs have been realized [13][14][15] since 2013 with pulse durations in the picosecond and femtosecond regime. However, due to the limited availability of pulsed laser systems in the red spectral range, only few characterization measurements on the SESAM parameters 16 have been performed. ...
... We use a v-shaped cavity, which has already been described previously. 14,16 The semiconductor structures are placed as end mirrors and the highly reflective output coupler with a radius of curvature of 50 mm acts as folding mirror. The distances of the two resonator arms are adjusted for a minimum spot size of the laser mode on the SESAM (diameter ∼ 20 µm) and a mode diameter of ∼ 100 µm on the gain chip to ensure the absorber saturates at lower pulse energies. ...
We present a passively mode-locked AlGaInP-VECSEL fabricated by metal-organic vapor-phase epitaxy emitting at around 655 nm. This wavelength region is reached by using InP-QDs in the active zone of the gain structure and the SESAM. Both semiconductor structures have a near anti-resonant design with the QD layers embedded in Al0.10GaInP barriers and Al0.55GaInP cladding layers. The repetition frequency of the emitted pulse train is about 850 MHz. Due to the intra-cavity use of a plane diamond heat spreader, side pulses are observed with a pulse duration of the single pulses in the order of one picosecond.
