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A new design of vertical external cavity surface emitting laser (VECSEL) with diamond-based high contrast gratings is proposed. The self-consistent model of laser operation has been calibrated based on experimental results and used to optimize the new proposed device and to perform comparative thermal and optical analysis of conventional and double...
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Citations
... Additionally, at least one of the cavity mirrors is separated from the structure, and a concave output coupling mirror is used to stabilize the cavity and shape the mode. These structures should have better power scalability due to their spatially uniform optical pumping, much lower thermal stresses [46], and better thermal management [47]. ...
The goal and essential parameter of laser light conversion is achieving emitted radiation of higher brightness. For many applications, the laser beam must have the highest available beam quality and highest achievable power. However, lasers with higher average power values usually have poorer beam quality, limiting the achievable brightness. Here, we present a method for improving the beam quality by using a spatially structured optical pump for a membrane external cavity laser resonator. An increase in brightness is achieved under fixed focusing conditions just by changing the pump intensity profile. A controllable output laser mode can be achieved by using a dynamically changing pump pattern.
... In terms of general performance, both types of optically pumped surface emitting semiconductor lasers with external cavity, i.e. vertical-external-cavity surface-emitting lasers (VECSELs) [3], [4], and MECSELs, can deliver Watt-level diffraction limited beams in a broad wavelength range benefiting from excellent thermal management enabled by the thin-disk gain architecture. Yet, the MECSEL allows for improved thermal management linked to the use of two heat-spreaders in immediate proximity of the active region [5], [6]. Additional power scaling can be obtained by employing double side [7] or multi-pass pumping [8]. ...
... On the same line, the ability of MECSELs to achieve a broader wavelength tunability [11] and to implement a design optimized towards mode-locking operation [12] has been also demonstrated. In terms of thermal management, the expected benefits of using two heat-spreaders [5], have been recently experimentally proven to be typically larger than a factor of two [13] when using two instead of one single heat-spreader. Consequently, the double heat-spreader approach has become a standard in MECSELs [14], [15]. ...
The operation of a semiconductor membrane external-cavity surface-emitting laser (MECSEL) employing a gain membrane with a cavity design, which is non-resonant regarding the two semiconductor - heat-spreader interfaces, is presented. The MECSEL delivers watt-level output power, in line with state-of-the-art results. The study provides new evidence that the design criteria of a MECSEL gain region are significantly relaxed compared to active regions employing distributed Bragg reflectors, for which the field distribution is set by the Bragg condition leading to tight tolerances for positioning of the emitting quantum structures. The study has relevance especially for the development of mode-locked MECSELs by minimizing the impact of defective Fabry-Pérot micro-cavity effects due to reflections between the semiconductor gain structure and the two heat-spreader elements placed on each side of the semiconductor membrane.
... In general, metals provide better cooling due to their higher values of thermal conductivity compared to semiconductors (by one order of magnitude) or dielectrics (by two orders of magnitude), while also being able to enhance the reflectivity. Simulations show that combining a thermally higher-conductive heatsink like diamond next to the active region outperforms those that have a DBR placed in between in terms of temperature rise within the active region [19,21]. Therefore, an optimized temperature control for the MESAM using a high quality intracavity diamond in combination with improved processing and bonding appears as an interesting package towards improved high-power mode locking. ...
We present a new saturable absorber device principle which has the potential for broad spectral range applications. An active region membrane is separated from the substrate and placed on a dielectric end mirror. By combining the absorbing membrane with the dielectric mirror to one device we get a membrane saturable absorber mirror (MESAM) which is similar to the well-known semiconductor saturable absorber mirror (SESAM) without the restriction of the stop-band reflectivity of the distributed Bragg reflector (DBR). Stable mode-locking with the MESAM was achieved in a red-emitting VECSEL at a pump power of 4.25 W with a pulse duration of 3.06 ps at 812 MHz repetition rate. We compare the performance and pulses of both SESAM and MESAM in a z-shaped VECSEL cavity.
... where the QWs are InP-based rendering impossible the use of GaAs/AlGaAs DBRs. To overcome the spectral limitations of the DBR and to some extent also improve the operation of the gain heterostructure by better thermal management, an alternative laser concept has emerged, the membrane external-cavity surface-emitting laser (MECSEL) [5][6][7] . In a MECSEL the gain medium is comprised only of the thin QW or QD heterostructure (without a DBR), which is then used in an external cavity architecture. ...
A membrane external-cavity surface-emitting laser (MECSEL) with an InAs/InP quantum dot (QD) based gain region is demonstrated. The pumping scheme employs a 90° off-axis parabolic mirror to focus the diode laser pump beam to a nearly circular pump spot. With this pump arrangement, the QD MECSEL with SiC heat spreaders produced 320 mW output power at room temperature with direct emission in the near-infrared at 1.5 µm. We report a record value of 86 nm for the tuning range at this wavelength region, owing to a broad QD gain bandwidth and wide tunability in MECSELs.
... In this section we use a self-consistent model combining three-dimensional PWAM and two-dimensional thermal and electrical models based on finite element methods represented in cylindrical coordinates, together with diffusion and gain models that take into account numerous interactions as described with great detail in [40] and also described in S6. We already calibrated the parameters used in our numerical self-consistent model using the measured characteristics of electrically injected D-D VCSELs emitting at 980 nm as reported earlier [27,29,[41][42][43][44]. The designs of microcavities of the M-D and M-M VCSELs are appropriately modified with respect to the simple structure described earlier to enable current injection and radiative recombination of carriers in the active region. ...
Semiconductor planar microcavities significantly enhance the interaction between light and matter and are thus crucial as a fundamental research platform for investigations of quantum information processing, quantum dynamics, and exciton-polariton observations. Microcavities also serve as a very agile basis for modern resonant-cavity light-emitting and detecting devices now in large-scale production for applications in sensing and communication. The fabrication of microcavity devices composed of both common materials now used in photonics and uncommon or arbitrary materials that are new to photonics offers great freedom in the exploration of the functionalities of novel microcavity device concepts. Here we propose and carefully investigate two unique microcavity designs. The first design uses a monolithic high-index-contrast grating (MHCG) and a distributed Bragg reflector (DBR) as the microcavity mirrors. The second design uses two MHCGs as the microcavity mirrors. We demonstrate by numerical analysis that MHCG-DBR and MHCG-MHCG microcavities, whose lateral radial dimension is 16 μm, reach very large quality factors at the level of 10 ⁴ and nearly 10 ⁶ , as well as purposely designed wavelength tuning ranges of 8 and 60 nm in both configurations, respectively. Our MHCG-MHCG microcavities with a very small size of 600 nm in the vertical dimension show extremely large quality factors, which can be explained by treating the optical modes as quasi-bound states in a continuum (BICs). Moreover, we verify our theoretical analysis and calibrate our simulation parameters by comparing to the experimental characteristics of an electrically injected MHCG-DBR microcavity vertical-cavity surface-emitting laser (VCSEL) emitting at a peak wavelength of about 980 nm. We use the calibrated parameters to simulate the emission characteristics of electrically injected VCSELs in various MHCG-DBR and MHCG-MHCG microcavity configurations to illustrate the influence of microcavity designs and their quality factors on the predicted lasing properties of the devices.
... We here pursue experimental investigations on the previously proposed double-diamond high-contrast-gratings VECSEL design [11], with the important modification, that the high contrast gratings (HCG) are etched directly into the diamond substrate instead of consisting of a deposited silicon layer, therefore enabling enhanced heat dissipation by the single crystal diamond. Our fabrication approach has been facilitated by the significant advances in fabrication technology of Chemical Vapor Deposition (CVD) single crystal diamond plates in recent years [12][13][14][15]. ...
... Compared to this design, in our configuration, all the DBRs of the bottom mirror were replaced by a HCG and an output coupler was employed as a top mirror. Furthermore, instead of applying a secondary layer as in [11], our proposed HCG is fabricated directly in the single crystal diamond, therefore integrating also the heatsink into the same https://doi.org/10.1016/j.diamond.2020.107744 Received 20 December 2019; Received in revised form 31 January 2020; Accepted 4 February 2020 component. ...
... The initial parameters of the HCG were determined based on a previous study [11], and then were optimized by an iterative numerical simulation approach. The parameter search and optimization was performed based on the rigorous coupled wave analysis-based (RCWA) method [22] within a MatLab environment. ...
We report on the design, fabrication and optical performance of gain mirrors in single crystal diamond substrates for vertical external cavity surface emitting lasers (VECSELs). VECSELs have gained attention recently due to their potential for high emission power in single mode with low beam divergence, yet their maximum output power remains typically limited due to thermal roll-over resulting from insufficient heat dissipation. In order to increase the heat transfer, we exploit the excellent thermal conductivity of single crystal diamond, which is assembled in direct contact with the active structure. The optical cavity is hereby defined by an output coupler and a high reflection grating structure etched into the diamond surface. We here present the design and microfabrication of a diffraction grating that was optimized to reflect light into the 0th order, therefore combining the role of a gain mirror and a heatsink at the same time. Our process involved metal mask deposition onto the diamond surface, e-beam lithography and reactive ion etching. Characterization showed reflection above 95% at a center wavelength of 1550 nm, potentially allowing the integration of the diamond mirror into a vertical external cavity surface emitting laser.
... As a result, DBRs are typically a few micrometers thick and have a comparatively small thermal conductivity [10][11][12]. Therefore, it is beneficial to use an alternative laser architecture in which the gain region is operated in transmission and the DBR function is taken by an external mirror; this allows implementing the double-side cooling for the gain region as recently proposed for membrane external-cavity surface-emitting lasers (MECSELs) [13][14][15]. ...
We present a membrane external-cavity surface-emitting laser (MECSEL) operating around 825 nm at room temperature. With a tuning range of 22 nm, the MECSEL fills the spectral gap between 810 nm and 830 nm, and extends the wavelength coverage of this category of high-beam-quality semiconductor lasers. For high-power operation, the pump spot size and cavity mode size can be enlarged in MECSELs. We apply this technique and demonstrate power scaling. The maximum output power is increased from 0.7 W to 1.4 W. Investigations on the beam quality reveal thermal lensing with a marginally changing $ {M^2} $ M 2 value close to the diffraction limit.
... A third power scaling approach utilizes double-side cooling, where the gain element is used as a transmissive element, as illustrated in figure 4(e). The benefits of such 'DBR-free VECSELs' consisting solely of the gain region have been recently explored in [74,75]. Another more exploratory design was demonstrated in [76], where the gain element was contacted onto a prism and total internal reflection was used instead of a DBR. ...
Vertical-external-cavity surface-emitting lasers (VECSELs) are the most versatile laser sources, combining unique features such as wide spectral coverage, ultrashort pulse operation, low noise properties, high output power, high brightness and compact form-factor. This paper reviews the recent technological developments of VECSELs in connection with the new milestones that continue to pave the way towards their use in numerous applications. Significant attention is devoted to the fabrication of VECSEL gain mirrors in challenging wavelength regions, especially at the yellow and red wavelengths. The reviewed fabrication approaches address wafer-bonded VECSEL structures as well as the use of hybrid mirror structures. Moreover, a comprehensive summary of VECSEL characterization methods is presented; the discussion covers different stages of VECSEL development and different operation regimes, pointing out specific characterization techniques for each of them. Finally, several emerging applications are discussed, with emphasis on the unique application objectives that VECSELs render possible, for example in atom and molecular physics, dermatology and spectroscopy.
... Recently, to further improve heat extraction two new designs of the VECSEL laser have been proposed (Iakovlev et al. 2014;Yang et al. 2015). In both of those designs the active region was separated from the DBR. ...
... In both of those designs the active region was separated from the DBR. Iakovlev et al. (2014) proposed an active region to be enclosed from both sides by two transparent diamond heat-spreaders (after removing the substrate) and that a mirror was engraved as High Contrast Grating on the outside surface of one of those diamonds. The second mirror enclosing the resonator was designed as a self-standing dielectric one. ...
We compare the heat extraction efficiency for a standard Vertical External Cavity Surface-Emitting Laser and the distributed Bragg reflector (DBR)-free structure employing a single and double diamond heat-spreaders, respectively. Both heterostructures grown by Molecular Beam Epitaxy employ two identical active regions designed for emission at 980 nm. We show that the thermal resistance has been decreased 15 times when there is no DBR and heat is extracted from both side of active region. For DBR-free laser no thermal rollover of power conversion characteristic was observed in the range of considered input powers.
... This could be realized by growing the active region directly on the substrate (without the DBR), then removing the substrate, and finally embedding the released active region membrane between two transparent intracavity heat spreaders (made of diamond or silicon carbide). This concept for improving the cooling of a compact VECSEL has already been theoretically studied and simulated, 11 and a DBR-free VECSEL (with a released active region bonded to one side of an intracavity heat spreader) has also been realized recently. 12 In another approach to improve the thermal properties of VECSELs, we have recently performed experiments to illustrate a proof-of-principle semiconductor membrane external-cavity surface-emitting laser (MECSEL). ...
An optically pumped device features a semiconductor membrane sandwiched between diamond heat spreaders to maximize heat dissipation from the active region.
