Mode-locked Solid-state Lasers Research Articles

Kerr-lens mode-locking of an Yb:SALLO laser generating 25 fs pulses at 1090 nm

We report on the generation of sub-30 fs pulses from a Kerr-lens mode-locked ytterbium solid-state laser based on a disordered Yb:SrLaAlO4 (Yb:SALLO) crystal as a gain medium. The Yb:SALLO laser, pumped by a spatially single-mode Yb-fiber laser at 979 nm, produces soliton pulses as short as 25 fs at 1090 nm, with an average output power of 149 mW at a pulse repetition rate of ∼80.7 MHz. The power scaling potential of the Kerr-lens mode-locked laser is exploited by achieving watt-level (1.54 W) average output power at 1081 nm for a somewhat longer pulse duration of 34 fs. This result corresponds to an impressive laser efficiency of 49.7% and a peak power of 468 kW.

Investigation of low pulse repetition passively mode-locked Nd:YVO4 lasers via multi-pass periodic trajectories in a confocal cavity.

We derive the parametric equations for the geometric rays of a periodic orbit inside a confocal cavity. Based on the derived formula, we demonstrate a passively mode-locked solid-state laser with a low pulse repetition rate to obtain a pulse train traveling along zigzag multi-pass trajectories. We achieve a stable mode-locked pulse train with a pulse repetition rate of 18 MHz by designing the cavity to satisfy the dual-M trajectory. Furthermore, by precisely adjusting cavity mirrors under the same experimental setup, we can reach pulse repetition rates of 12 and 9 MHz for the mode-locked laser. It is believed that the numerical calculation and the developed experiment can provide a straightforward and convenient way to achieve a low pulse repetition rate for passively mode-locked lasers.

Prompt Analysis and Design for Passively Mode-Locked Solid-State Lasers with Semiconductor Saturable Absorbers

The critical pump power for achieving passively continuous-wave mode-locking in a solid-state laser is analytically derived from the spatially dependent rate equations and the criterion for the intracavity pulse energy. A prompt way is proposed to straightforwardly design the cavity for passively mode-locked solid-state lasers. Complete experiments are performed to demonstrate the proposed cavity design and, simultaneously, to verify the theoretical model for the critical pump powers. It is interestingly observed that even though a larger modulation depth causes a higher critical pump power, it can generate a shorter pulse width in return.

Real-Time Exploration on Buildup Dynamics of Diode-Pumped Passively Mode-Locked Nd:YVO4 Laser with SESAM

The buildup dynamics of diode-pumped passively mode-locked solid-state laser is thoroughly explored using the real-time measurement with temporal sampling rate of up to 40 GHz. A concise cavity is developed to ensure the transient dynamics purely arising from the gain medium and saturable absorber. Experimental results reveal that the laser output in the buildup process exhibits numerous passively Q-switched pulses followed with a damped relaxation oscillation prior to the stable mode locking. Furthermore, it is confirmed that the laser output has already displayed single clean mode-locked pulses inside the first several Q-switched envelopes before stepping into the stage of relaxation oscillation. The present real-time exploration is expected to provide important information for practical applications with temporal modulation of the pump intensity.

44-fs pulse generation at 2.05 µm from a SESAM mode-locked Tm:GdScO3 laser.

Pulses as short as 44 fs (6 optical cycles) with a spectral width of 120 nm are generated from a mode-locked solid-state laser near 2 µm employing an orthorhombic Tm:GdScO3 perovskite crystal. The average power amounts to 188 mW at a repetition rate of ∼77.6 MHz. The strong inhomogeneous line broadening in GdScO3 suggests optimum conditions for few-optical-cycle pulse generation of rare-earth ion doped GdScO3 bulk lasers.

Mode-locked laser oscillation with spectral peaks at molecular rovibrational transition lines.

We demonstrate spectral peak formation in a mode-locked solid-state laser that contains a gas cell inside the cavity. Symmetric spectral peaks appear in the course of sequential spectral shaping through resonant interaction with molecular rovibrational transitions and nonlinear phase modulation in the gain medium. The spectral peak formation is explained as that narrowband molecular emissions triggered by an impulsive rovibrational excitation are superposed on the broadband spectrum of the soliton pulse by constructive interference. The demonstrated laser, which exhibits comb-like spectral peaks at molecular resonances, potentially provides novel tools for ultrasensitive molecular detection, vibration-mediated chemical reaction control, and infrared frequency standards.

Behaviors of multiple pulsing in high power saturable-absorber mode-locked Yb:KGW laser

By investigating the mode-locked pulse characteristics with varying pump power, we report on the soliton pulse breakup and multiple pulsing of a high power femtosecond Yb:KGW laser at a 10 W level of output power. The pulse breakup from single to double pulses at an output power of 6.3 W, exhibits a step-like abrupt change in the spectrum and temporal duration. Even under multiple pulsing operation, the mode-locked pulses follow the soliton-like pulse formation model such that the pulse duration is inversely proportional to the pulse energy and the time-bandwidth product is close to the transform limit. The multiple pulsing and breakup characterized in this study provide an efficient and reliable method to confirm the single pulse operation of high power mode-locked solid-state lasers.

High Beam Quality and High Power Mode-locked Solid-state Laser for Photocathode Drive Laser System

High Beam Quality and High Power Mode-locked Solid-state Laser for Photocathode Drive Laser System

Stoichiometric modulation on optical nonlinearity of 2D MoS x Se2−x alloys for photonic applications

Abstract The composition-engineered band structures of two-dimensional (2D) ternary transition-metal dichalcogenides (TMDCs) semiconductor alloys directly dominate their electronic and optical properties. Herein, in this paper, a detailed theoretical and experimental study on the composition-dependent nonlinear optical properties of 2D MoS x Se2−x alloys was carried out. The first-principles calculations were performed to investigate the compositionally modulated properties of monolayer 2D MoS x Se2−x (x = 0.25, 0.5, 1.0, 1.5, and 1.75) in terms of the carrier effective mass, carrier density and mobility, as well as band-gaps. Furthermore, high-quality few-layered MoS x Se2−x (x = 0.2, 0.5, 1.0, 1.5, and 1.8) nanosheets were fabricated by using liquid phase exfoliation method. The third-order nonlinear optical response was investigated by open-aperture Z-scan technique, revealing composition-dependent saturable absorption, and light modulation properties, which were correlated to the theoretical calculations and further confirmed by using MoS x Se2−x nanosheets as saturable absorbers (SAs) for all-solid-state pulsed lasers. In particular, a mode-locked solid-state laser with pulse width of 227 fs was realized with MoS0.2Se1.8 as SA, for the first time to our best knowledge. Our work not only provides a comprehensive understanding of the compositionally and defectively modulated nonlinear optical responses of ternary TMDCs alloys, but also paves a way for the development of 2D materials-based novel optoelectronic devices.

Kerr-lens mode-locked Tm-doped sesquioxide ceramic laser.

Kerr-lens mode-locked solid-state laser operation at ∼2µm is investigated. Using a Tm3+-doped (Lu,Sc)2O3 "mixed" sesquioxide ceramic as a gain medium, pulses as short as 58 fs are generated at ∼2081nm via soft-aperture Kerr-lens mode locking. The average output power amounts to 220 mW at a pulse repetition rate of 84.8 MHz. The emitted spectrum at the long-wavelength wing extends to >2.2µm which is attributed to vibronic transitions of the Tm3+ ions. The latter is found to be essential for generating pulses with durations in the 50 fs range.

Intra-oscillator broadband THz generation in a compact ultrafast diode-pumped solid-state laser.

We demonstrate broadband and powerful terahertz (THz) generation at megahertz repetition rate based on intra-oscillator optical rectification (OR) in gallium phosphide (GaP). By placing the nonlinear crystal directly inside the cavity of a Kerr-lens mode-locked ultrafast diode-pumped solid-state laser (DPSSL) oscillator, we demonstrate a compact and single-stage THz source. Using only 7 W of diode-pump power, we drive OR in a GaP crystal with 22 W of average power at ∼80 MHz repetition rate. In a first configuration, using a 0.3-mm-thick GaP and 105 fs driving pulses, we generate up to 150 µW of THz radiation with a spectrum extending to 5.5 THz. In a second configuration allowing for sub-50-fs pulse duration, we generate up to 7 THz inside a 0.1-mm-thick GaP crystal. This performance is well suited for THz time-domain spectroscopy and THz imaging. Intra-oscillator THz generation in sub-100-fs DPSSLs is a promising way to scale down footprint, complexity and cost of powerful broadband THz sources.

Ultraflat Langmuir–Blodgett assembled graphene oxide saturable-absorber films for pulsed near-infrared laser generation

Large-scale production of ultraflat broadband saturable-absorber films is highly desired for passive mode-locked solid-state lasers. However, the current vapour deposition and spin coating routes for fabricating saturable absorbers (SAs) are suffering from the limited flexibility in substrate choice and complexity of mass production processes. Here, we demonstrate an ultraflat carboxyl-functionalized graphene oxide (GO-COOH) SA film via Langmuir–Blodgett (LB) assembly for solid state laser mode-locking. Hydrophilic carboxyl groups from GO sheets weaken the aggregation effect thus contribute to the uniform and stable dispersion of GO sheets in water. Such GO suspensions are made into an ultrathin large-area graphene-based SA film by a LB assembly process ensuring high surface uniformity. The room-temperature and highly repeated operation for GO LB films avoids the thermal damage of GO sheets and improves the membrane repeatability. Consequently, the ultrathin GO-COOH SA shows the modulation depth (2.3%) and low saturation intensity (24.7 KW cm−2) under 1064 nm laser irradiation. By inserting the GO SA into a Nd:GdVO4 laser, both passive Q-switched (QS) and passive Q-switched mode-locked (QML) operations are also attained. The slope efficiency of QS laser is up to 35.6% and the maximum single pulse energy is 1.48 μJ. In particular, the QML pulses can be achieved stably and repeatedly with an average output power of 1.33 W and a pulse energy of 13.2 nJ. Our strategy provides a new concept for improving the modulation stability of graphene-based SAs and promoting their industrial application in pulsed solid-state lasers.

All-solid-state mode-locked 1064 nm Nd:YVO4 laser with Fe[formula omitted]O[formula omitted] nanoparticles saturable absorber

In this work, ferroferric-oxide (Fe3O4) nanoparticles (FONPs) were used as saturable absorber (SA) for passively mode-locked solid-state lasers (SSLs). Based on the interaction between laser and FONPs, a continuous mode-locked operation was achieved. Results showed that FONPs had a large nonlinear saturated absorption property at 1μm. We obtained a mode-locked operation with a pulse duration of 463 ps at 125 MHz repetition rate using this novel SA. The maximum average output power, single pulse energy, and peak power of mode-locked laser were 856 mW, 6.85 nJ, and 14.79 W, respectively. To the best of our knowledge, this study is the first to achieve a passively mode-locked SSL operation with FONPs as the SA.

SWCNT-SA mode-locked Tm:LuYO3 ceramic laser delivering 8-optical-cycle pulses at 2.05 µm

Passive mode locking of a T m : L u Y O 3 ceramic laser in the 2 µm spectral region is demonstrated by employing a single-walled carbon nanotube-saturable absorber. Almost chirp-free pulses as short as 57 fs, i.e., 8 optical cycles are produced at a repetition rate of 72.6 MHz (63 mW average power). The corresponding optical spectrum centered at 2045 nm, exhibits a bandwidth of 80 nm, which corresponds to almost chirp-free pulses. To the best of our knowledge, the results represent the shortest pulses generated by mode-locked Tm solid-state lasers.

Recent Advances in the Photonic Integration of Mode-Locked Laser Diodes

Mode-locked fiber and solid state lasers have played an essential role in several scientific and technological developments. The integration of mode-locked lasers on chips could enable their use in a wide range of applications. The advancement of semiconductor mode-locked laser diodes has been going on for several decades, but has recently seen the development of novel devices based on generic InP and III-V-on-silicon photonic integration platforms. These photonic integration platforms enable the use of standardized components and low-loss waveguides within the laser cavity, allowing for the design of advanced extended cavities. In this manuscript we give a review of these novel devices and compare their performance.

Passively Mode-Locked Solid-State Laser With Absorption Tunable Graphene Saturable Absorber Mirror

Two-dimensional layered materials have attracted huge interest in the generation of ultrafast laser for their excellent saturable absorption properties. However, it is still challenging to precisely control their saturable absorption properties. Here, by alternatively changing the electric field intensity on the surface of high-reflection mirror, we successfully control the nonlinear absorption properties (e.g., saturable fluence, modulation depth) of graphene-based saturable absorber mirrors (GSAM) at the optical telecommunication wavelength of 1.3 μm and their applications in solid-state lasers for the first time. Modulation depth of 1.2% is obtained from a GSAM with deposition of a λ/8 (λ = 1.3 μm) thick SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer between the monolayer graphene and a high-reflection mirror, while modulation depth is increased to 4.3% with a λ/4 thick SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer insertion in another GSAM. Pulses with the duration of 20 ps (λ/8 thick SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> insertion) and 7.4 ps (λ/4 thick SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> insertion) are achieved, respectively, based on the two mirrors. Our results indicate that this method is easy and reliable to versatility modulate the saturable absorption properties of other two-dimensional layered materials beyond graphene for the generation of ultrafast solid-state lasers.

Compact solid-state waveguide lasers operating in the pulsed regime: a review [Invited

Over the last years, there has been tremendous progress with compact pulsed lasers based on various solid-state gain media, such as crystals and glasses doped with laser-active ions. With the integration of increasingly diverse saturable absorber materials, these small sources are capable of delivering stable pulses with durations as short as femtoseconds and repetition rates exceeding 10 GHz. These promising sources are known as solid-state waveguide lasers, which have become synonymous with miniaturization, integration, and functionality. This article overviews the progress in the development of passively Q-switched and mode-locked solid-state waveguide lasers employing diverse saturable absorbers. The most commonly used laser configurations, state-of-the-art waveguide fabrication techniques, and experimental demonstrations of pulsed waveguide lasers are summarized and reviewed. Selected well-noted topics, which may shape the future directions in this field, are also presented.

Narrowing spectral linewidth in passively mode-locked solid-state lasers.

A novel scheme to realize a mode-locked laser with a narrow spectral linewidth is demonstrated by exploiting a reflected Fabry-Perot (FP) cavity to introduce an intense FP effect. Stable continuous-wave mode-locked operation is achieved with the repetition rate of 48MHz and the maximum average output power of 2.6W under an incident pump power of 11.9W. The mode-locked pulse width is systematically investigated by varying the optical thickness of the reflected FP cavity. The pulse duration is experimentally found to be in a range of 0.8 to 2.6ns. The experimental results reveal that the reflected FP cavity is the key factor leading to the pulse generation in the nanosecond regime. This Letter is believed to provide a promising method for generating optical pulses with narrow spectral linewidths.

Ultralow Saturation Intensity Topological Insulator Saturable Absorber for Gigahertz Mode-Locked Solid-State Lasers

The successful demonstration of Q-switched and mode-locked fiber-laser operations using a topological insulator (TI) as saturable absorber (SA) has opened an application window besides TI's originally expected features. However, to date, all-solid-state mode-locked lasers base on TISAs are still unavailable and became a desired goal not only due to their application as light sources, but also because of providing a way for deeper investigation of the nature of ultrafast dynamics present in TISAs. In this paper, the realization of a continuous-wave mode-locked all-solid-state laser with a repetition rate of around 1 GHz is reported using a high-quality TI SA mirror (TI-SAM) with ultralow saturation intensity, fabricated by a spin coating-co-reduction approach. An output power of 180 mW and pulse duration of 8 ps are observed. In addition, a 61 dB pulse-train quality from the radio frequency spectrum of mode-locked operation prove the feasibility of the proposed laser. To the best of our knowledge, this is the first experimental demonstration of a mode-locked solid-state laser based on TIs. In addition, this paper shows that the use of TISAs is a promising option for the realization of scaling solid-state mode-locked lasers with higher repetition rates, reaching order of GHz.

Recent Progress in Broadband Carbon Nanotube Saturable Absorbers for Ultrafast Bulk Solid-State Lasers

Carbon nanotubes (CNTs) are one of the most investigated nanomaterials for a variety of applications due to their unique electronic and optical characteristics. Over the last two decades, CNTs have been widely investigated to develop efficient passive mode-locking devices applicable for diverse ultrafast laser systems, because they exhibit high nonlinearity, photo-excited ultrafast carrier recovery, broadband applicability and relatively easy processes for device fabrication. In this overview article, recent progress of CNT-based saturable absorbers applicable for mode-locking ultrafast bulk solid-state lasers operating in a broad spectral range between 800 nm and 2100 nm will be reviewed.