We demonstrate for the first time the calibration of the wavelength scale of high-performance spectrometers using a fully stabilized optical frequency comb from an ultrafast optically pumped semiconductor disk laser (SDL) as a traceable reference. The SDL is a modelocked integrated external-cavity surface-emitting laser (MIXSEL) with the gain and saturable absorber layers fully integrated into one wafer chip, which forms one end mirror of the simple straight cavity with a pulse repetition rate of 11 GHz. This MIXSEL comb is actively stabilized and opens new possibilities for easier and more accurate frequency calibrations of standard laboratory instruments.

Optically pumped passively modelocked vertical external-cavity surface-emitting lasers (VECSELs) can generate pulses as short as 100 fs with an intracavity semiconductor saturable absorber mirror (SESAM). Very stable soliton modelocking can be obtained, however, the high-Q-cavity, the short gain lifetime, and the kinetic-hole burning can also support rather complex multipulse instabilities which we analyze in more details here. This onset of multipulse operation limits the maximum average output power with fundamental modelocking and occurs at the roll-over of the cavity round trip reflectivity. Unfortunately, such multipulse operation sometimes can mimic stable modelocking when only limited diagnostics are available.

We demonstrate for the first time that a fully stabilized ultrafast semiconductor disk laser is a suitable tool to perform wavelength calibration of high-performance spectrometers, opening new possibilities for wider and more accurate instruments calibrations.

We present dual-comb spectroscopy on water vapor with a free-running modelocked semiconductor disk laser. The simple and compact laser emits simultaneously two gigahertz pulse trains with slightly different pulse repetition rates from a single cavity.

Ultrafast vertical external-cavity surface-emitting lasers (VECSELs) are versatile laser sources and feature high-power operation. To date the best modelocking results have been achieved with a semiconductor saturable absorber mirror (SESAM). Ultrafast optically pumped semiconductor disk lasers (SDLs) are compact, cost-efficient and provide excellent beam quality at gigahertz pulse repetition rates for applications such as for example multi-photon imaging, ultrafast communication and in particular self-referenced gigahertz frequency combs. The highest peak power obtained with an ultrafast VECSEL is 4.35 kW in 400-fs pulses and the shortest pulses until now are 107 fs at 3 mW average output power. Here we present a SESAM-modelocked VECSEL with pulses as short as 96 fs and 100 mW average output power. These are to the best of our knowledge the shortest pulses achieved by a fundamentally modelocked SDL and result in a very high peak power of 0.56 kW at a pulse repetition rate of 1.63 GHz. The short pulse duration was achieved by introducing a small amount of positive group delay dispersion with a single path through an external 2-mm thick ZnSe window plate that compensated the initially negatively chirped 107-fs output pulses. Currently the power is limited by the transition from fundamental modelocking to multi-pulse operation, which reduces the pulse peak power and introduces additional noise. Therefore, we present a study of the multi-pulse behavior of the high-power 100-fs SDL resulting from the complex modelocking mechanism. This study also provides an insight into special issues of pulse characterization that may suggest stable fundamental modelocking even if this is not the case.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text D. Waldburger, S. M. Link, C. G. E. Alfieri, M. Golling, and U. Keller, "Coherent Beam Combining of a Colliding Pulse Modelocked VECSEL," in Laser Congress 2017 (ASSL, LAC), OSA Technical Digest (online) (Optica Publishing Group, 2017), paper AW4A.5. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Ultrafast optically pumped semiconductor disk lasers (SDLs) provide an enabling combination of gigahertz pulse repetition rates, short pulse durations, high peak power and good beam quality. However, the successful demonstration of shorter pulse durations with pulses as short as 100 fs has come at the expense of lower optical-to-optical pump efficiency for ultrafast SDLs based on active InGaAs quantum wells (QWs). The optical pump efficiency, which also depends on the pulse repetition rate, decreases with the pulse duration to values typically below 1% in the sub-300-fs regime. For a better understanding of this trade-off between shorter pulse durations and optical efficiency we present an empirical model based on three time constants: the carrier lifetime in the conduction band, the time required for a pulse to empty the carrier reservoir of a QW and the time needed to refill the QW through the continuously pumped GaAs barriers. With the time constants used as fitting parameters we obtain a reasonably good agreement for the measured efficiency of all previously published MIXSEL results. Furthermore we have investigated the SDLs gain dynamics and our measurements have confirmed that shorter pulses significantly reduce the gain saturation fluence. A simplified description of the QWs as a 3-level system could accurately reproduce the gain saturation curves and let us identify spectral hole burning as the main cause of the reduced gain and efficiency. This will be a challenge for further improvements of the ultrafast performance of ultrafast SDLs based on InGaAs QWs.

Summary form only given. Passively modelocked optically pumped semiconductor disk lasers (SDLs) [1] based on InGaAs quantum wells (QWs) such as vertical external-cavity surface-emitting lasers (VECSELs) or modelocked integrated surface-emitting lasers (MIXSELs) are an appealing ultrafast laser technology for applications that require compelling combinations of short femtosecond pulses and gigahertz pulse repetition rates. Recent development of pulse shortening strategies resulted in record-short 107-fs pulses from a VECSEL [2] and 253-fs pulses from a MIXSEL [3]. However, this progress in shorter pulse durations has come with the trade-off of significantly lower optical-to-optical pump efficiency even below 1% and only moderate average output power of around 100 mW so far.Here, we develop a rate equation model to investigate the carrier dynamics in the SDL gain and absorber QWs with the aim to better understand the underlying physical reasons for this trade-off. In contrast to ab initio approaches [4], our goal is to simplify the model and still obtain full agreement with our experimental results.

We demonstrate the utility of femtosecond semiconductor disk lasers for multi-photon microscopy with several in vivo imaging experiments. These compact and affordable short pulse lasers are promising new sources for widespread bio-imaging.

Compact optically pumped passively modelocked semiconductor disk lasers (SDLs) based on active quantum wells (QWs) such as vertical external-cavity surface-emitting lasers (VECSELs) or modelocked integrated external-cavity surface-emitting lasers (MIXSELs) are wavelength-versatile sources that offer a unique combination of gigahertz pulse repetition rates and short pulse durations. In this paper, we present record-short pulses of 184 fs from a gigahertz MIXSEL emitting at a center wavelength of 1048 nm. This result comes at the expense of low optical-to-optical pump efficiency (<1%) and average output power limited to 115 mW. We experimentally observe that shorter pulses significantly reduce the macroscopic gain saturation fluence and develop a QW model based on rate equations to reproduce the gain saturation behavior and quantitatively explain the VECSEL and MIXSEL modelocking performances. We identify spectral hole burning as the main cause of the reduced gain at shorter pulse durations, which in combination with the short lifetime of the excited carriers strongly reduces the optical pump efficiency. Our better understanding will help to address these limitations in future ultrafast SDL designs.

A dual-comb modelocked semiconductor disk laser generates simultaneously two optical frequency combs from a single cavity using an intracavity birefringent crystal. This free-running laser enables free-running dual-comb spectroscopy on water vapor.

Dual-comb spectroscopy offers the potential for high accuracy combined with fast data acquisition. Applications are often limited, however, by the complexity of optical comb systems. Here we present dual-comb spectroscopy of water vapor using a substantially simplified single-laser system. Very good spectroscopy measurements with fast sampling rates are achieved with a free-running dual-comb mode-locked semiconductor disk laser. The absolute stability of the optical comb modes is characterized both for free-running operation and with simple microwave stabilization. This approach drastically reduces the complexity for dual-comb spectroscopy. Band-gap engineering to tune the center wavelength from the ultraviolet to the mid-infrared could optimize frequency combs for specific gas targets, further enabling dual-comb spectroscopy for a wider range of industrial applications.

We use an ultrafast diode-pumped semiconductor disk laser (SDL) to demonstrate several applications in multiphoton microscopy. The ultrafast SDL is based on an optically pumped Vertical External Cavity Surface Emitting Laser (VECSEL) passively mode-locked with a semiconductor saturable absorber mirror (SESAM) and generates 170-fs pulses at a center wavelength of 1027 nm with a repetition rate of 1.63 GHz. We demonstrate the suitability of this laser for structural and functional multiphoton in vivo imaging in both Drosophila larvae and mice for a variety of fluorophores (including mKate2, tdTomato, Texas Red, OGB-1, and R-CaMP1.07) and for endogenous second-harmonic generation in muscle cell sarcomeres. We can demonstrate equivalent signal levels compared to a standard 80-MHz Ti: Sapphire laser when we increase the average power by a factor of 4.5 as predicted by theory. In addition, we compare the bleaching properties of both laser systems in fixed Drosophila larvae and find similar bleaching kinetics despite the large difference in pulse repetition rates. Our results highlight the great potential of ultrafast diode-pumped SDLs for creating a cost-efficient and compact alternative light source compared to standard Ti: Sapphire lasers for multiphoton imaging.

For the first time, we use a stabilized dual-comb modelocked semiconductor disk laser to perform dual-comb spectroscopy. A water vapor absorption spectrum around 968 nm is measured with our very compact, simple and cost-efficient system.

This paper presents vertical external-cavity surface-emitting lasers (VECSEL) and mode-locked integrated external-cavity surface-emitting lasers (MIXSEL) structures emitting at 1 μm which currently generate record-short pulse durations for their respective technologies. A high-power 96-fs SESAM-modelocked VECSELs with 100 mW average output power at a pulse repetition rate of 1.63 GHz is demonstrated. The second VECSEL is similarly structured as the first one but is grown by molecular beam epitaxy instead of metalorganic vapor phase epitaxy and produces over 1 kW of pulse peak power with 101 fs pulses and an average output power of 150 mW at a pulse repetition rate of 1.12 GHz. The VECSELs are based on ten strain-compensated quantum wells (QWs) with an optimized distribution for a broad amplification bandwidth. The structural group delay dispersion (GDD) around the lasing wavelength is minimized, which is a key requirement for the record-short pulse durations. The VECSELs are modelocked by a QW SESAM in a V-shaped cavity together with a curved output coupler (OC). In a MIXSEL, the QW saturable absorber is integrated into the gain structure of a VECSEL, which allows together with a curved OC for modelocking in a simple straight linear cavity. Further optimization of the structural GDD and the coating of the sub-300-fs MIXSEL by Mangold et al. allowed to reduce the pulse duration to 184 fs with 115 mW of average output power at a pulse repetition rate of 4.33 GHz.

Optically-pumped SESAM-modelocked semiconductor disk lasers have become interesting ultrafast lasers with gigahertz pulse repetition rates, high average power and adjustable lasing wavelength. It is well established that colliding pulse modelocking (CPM) can generate both shorter pulses and improved stability. These improvements however typically come at the expense of a more complex ring cavity and two output beams. So far similar modelocking results have been obtained with CPM vertical external-cavity surface-emitting lasers (VECSELs) and with SESAM-modelocked VECSELs or modelocked integrated external-cavity surface-emitting lasers (MIXSELs) in a linear cavity. However coherent beam combining of the two output beams of a CPM VECSEL could result in a significantly higher peak power. This is interesting for example for applications in biomedical microscopy and frequency metrology. Here we demonstrate with a more detailed noise analysis that for both output beams of a CPM VECSEL the pulse repetition rates and the carrier envelope offset frequencies are locked to each other. In contrast to standard SESAM-modelocked VECSELs in a linear cavity, we only have been able to actively stabilize the pulse repetition rate of the CPM VECSEL by cavity length control and not by pump-power control. Furthermore, a first coherent beam combining experiment of the two output beams is demonstrated.