Bulk Laser Research Articles

MXene saturable absorber for nanosecond pulse generation in a mid-infrared Ho,Pr:LLF bulk laser

In this paper, high quality few-layer MXene-Ti3C2Tx was fabricated by the LPE method and successfully applied as saturable absorber for a passively Q-switched (PQS) Ho,Pr:LLF laser operating at 2.95 µm. The maximum average output power was determined to be 105 mW with a slope efficiency of 5%. The shortest pulse width and the largest pulse repetition rate were determined to be 266.7 ns and 83.24 kHz, corresponding to the single pulse energy and pulse peak power of 1.26 µJ and 4.73 W, respectively. It is the first demonstration of MXenes applied in mid-infrared (MIR) PQS solid-state bulk lasers, to the best of our knowledge. The results not only verify the broadband nonlinear saturable absorption properties of MXenes, but also pave the way for exploring their applications in photonic devices.

High-power and high-efficiency short wavelength operation of a Tm:YLF laser at 1.83 μm.

A high-power and high-efficiency diode-end-pumped Tm:YLF laser at 1.83μm is demonstrated for the first time, to our best knowledge. To make the laser operate at 1.83μm, a simple way of controlling the transmittance of the output coupler is used, and the criteria of the transmittance of the output coupler at the emission peaks of Tm:YLF are theoretically analyzed, which are verified by experimental results. Based on the theoretical analysis, laser oscillation at only 1.83μm is realized. Maximum output power at 1833nm is 8.5W with corresponding slope efficiency of 53.4% regarding absorbed pump power. In addition, tunability of this laser from 1827nm to 1837nm is obtained. Laser beam quality at 1833nm is measured to be 1.4 at maximum output power. The achieved laser performance represents considerable improvement compared to any other bulk laser emitting around 1.83μm.

Graphene mode-locked Tm,Ho-codoped crystalline garnet laser producing 70-fs pulses near 21 µm

Bilayer graphene synthesized by chemical vapor deposition is successfully applied as a saturable absorber (SA) for the passive mode-locking of a Tm,Ho:CLNGG laser at 2093nm. Near transform-limited pulses as short as 70 fs, i.e., 10 optical cycles, are produced at a 89 MHz repetition rate with 69 mW average output power. To the best of our knowledge, these are the shortest pulses ever reported from graphene-SA mode-locked Tm, or Ho-lasers in the 2 µm spectral region, including bulk and fiber lasers.

Mid-infrared Er:CaF2–SrF2 bulk laser Q-switched by MXene Ti3C2Tx absorber

We report a diode-pumped passively Q-switched Er:CaF2–SrF2 laser at 2.73 μm with MXene Ti3C2Tx as a saturable absorber (SA). A maximum average output power of the pulsed laser was measured at 286 mW, with a shortest duration of 814 ns and a repetition rate of 45.3 kHz. The corresponding single-pulse energy and peak power were calculated to be 6.32 μJ and 7.76 W, respectively. The results suggest the promising potential of MXene as an efficient SA for short pulse lasers in the mid-infrared spectral band.

Diode-pumped high-power sub-100 fs Kerr-lens mode-locked Yb:CaYAlO4 laser with 185 MW peak power

We demonstrated a diode-pumped high-power Kerr-lens mode-locked Yb:CaYAlO4 (Yb:CALYO) laser with a dual-confocal cavity, directly generating 59-fs pulses with 6.2 W average power, which is the highest average power from any sub-60 fs Yb-doped solid-state lasers. With the repetition rate of 50 MHz, the corresponding single pulse energy was 124 nJ and the peak power was 1.85 MW, which to the best of our knowledge is the highest peak power delivered directly from a sub-100 fs Yb-based bulk lasers ever.

Extreme and Topological Nonlinear Optics of Open Systems

A review of results of an investigation of the theory of optical wave packets with extreme properties with respect to a controllable pulse shape or to the complexity of the internal structure of radiation beam pulses is presented. Special attention is paid to the manifestations of dissipative effects of the electromagnetic energy inflow and outflow. Precisely these factors lead to peculiar rules of conservation of purely electromagnetic quantities in dissipative media, in which the electromagnetic energy irreversibly decreases in the case of absorption and increases with gain. These rules impose certain restrictions on the possibility of transformation of the shape of pulses and allow one to qualitative describe their evolution. A higher efficiency of the action of unipolar or quasi-unipolar radiation pulses on classical and quantum microobjects is shown and possible ways of formation of these pulses are discussed. For bulk laser media with saturable absorption, the topological properties of localized radiation structures and their transformations with a smooth change in the parameters of the medium (pump level) are described. The preservation of the topological structure upon changes in parameters within the stability range yields the possibility of their distinguishing when coding information by topological solitons of the considered type.

Sensitive saturable absorber and optical switch of epsilon-near-zero medium

We investigated the nonlinear absorption and optical switching properties of a typical Epsilon-near-zero (ENZ) thin film made of indium tin oxide (ITO) in the near-infrared region. ITO has a low saturable absorption intensity with the advantages of electric field enhancement. The Q-switching performance in the near-infrared region was demonstrated with the ITO as a passive Q-switcher in the bulk lasers for the first time, to the best of our knowledge. This work shows that ENZ materials have promising applications in ultrafast photonics and may be helpful for the development of further nonlinear optoelectronic devices.

Atomic dispensers for thermoplasmonic control of alkali vapor pressure in quantum optical applications

Alkali metal vapors enable access to single electron systems, suitable for demonstrating fundamental light-matter interactions and promising for quantum logic operations, storage and sensing. However, progress is hampered by the need for robust and repeatable control over the atomic vapor density and over the associated optical depth. Until now, a moderate improvement of the optical depth was attainable through bulk heating or laser desorption – both time-consuming techniques. Here, we use plasmonic nanoparticles to convert light into localized thermal energy and to achieve optical depths in warm vapors, corresponding to a ~16 times increase in vapor pressure in less than 20 ms, with possible reload times much shorter than an hour. Our results enable robust and compact light-matter devices, such as efficient quantum memories and photon-photon logic gates, in which strong optical nonlinearities are crucial.

Ytterbium calcium fluoride waveguide laser.

Calcium fluoride is a well-known material for optical components. It is also suited for doping with rare-earth ions, e.g., ytterbium ones. Yb:CaF2 is an efficient gain medium for high-power and ultrashort-pulse bulk lasers around 1 μm. We report on the first Yb:CaF2 planar waveguide laser. High-optical-quality single-crystalline waveguiding Yb:CaF2 thin films are grown on bulk CaF2 substrates by Liquid Phase Epitaxy. The spectroscopic study indicates the predominant coordination of isolated Yb3+ ions in trigonal oxygen-assisted sites, C3v(T2). The optical gain in Yb:CaF2 waveguide is demonstrated. A 1.4 at.% Yb:CaF2 planar waveguide laser generated 114 mW at 1037 nm with a slope efficiency of 12.9%. Yb:CaF2 films are promising for power-scalable waveguide mode-locked lasers and amplifiers.

1.83-μm high-power and high-energy light source based on 885-nm in-band diode-pumped Nd:YAG bulk laser operating on 4F3/2→4I15/2 transition.

We report on 1.8-μm laser generation based on a 885-nm diode laser in-band pumping of conventional Nd:YAG bulk crystal. The maximum output power reaches 2.72 W at 1834 nm with slope efficiency of about 12.1% with respect to the absorbed power. With a Cr:ZnSe saturable absorber, passively Q-switched operation is also demonstrated with maximum average output power of 1.25 W. The achieved shortest pulse width, maximum pulse energy and peak power are 54 ns, 125.9 μJ and 2.27 kW, respectively. The results are very competitive to many reported Tm3+ lasers at 1.9 μm. However, this 1834-nm wavelength is indeed difficult to generate from Tm3+ solid-state lasers, which bridges the wavelength gap for potential applications.

ReSe2 passively Q-switched Nd:Y3Al5 O12 laser with near repetition rate limit of microsecond pulse output

We first report on a stable ReSe2 passively Q-switched Nd:Y3Al5O12 bulk laser near room temperature, which can generate near-repetition rate limit of microsecond pulse output at full depth modulation. A new kind of two-dimensional transition metal dichalcogenide, ReSe2, is exploited as an excellent saturable absorber at 1.06μm with extremely high rate of loss modulation. The microsecond pulse repetition rate of as high as 274 kHz can be achievable under the pump power of 7.3 W, with the pulsewidth of 1.08μs and the pulse energy of 2.5 μJ. As the pump power varies from 4.4 to 7.3 W, the pulse repetition rate is tunable from 204 to 274 kHz. The good stability in operation is evaluated with power fluctuation less than 1%. The ultrahigh repetition rate of microsecond pulse source can be suitable for differential absorption lidar of monitoring atmospheric environment, which can meet the specific requirements of adequate interaction duration and sufficient sampling rate to improve the signal-to-noise ratio.

Influence of laser processing parameters on porosity in Inconel 718 during additive manufacturing

The melt pool characteristics in terms of size and shape and the porosity development in laser powder bed fusion–processed Inconel 718 were investigated to determine how laser power and scan speed influence the porosity in the microstructure. The melt pool characteristics developed with both single-track and multilayer bulk laser deposition were evaluated. It was found that the melt pool characteristic is critical for the porosity development. It is shown that the porosity fraction and pore shape change depending on the melt pool size and shape. This result is explained based on the local energy density of a laser during the process. High-density (> 99%) Inconel 718 samples were achieved over a wide range of laser energy densities (J/mm2). A careful assessment shows that the laser power and scan speed affect differently in developing the pores in the samples. The porosity decreased rapidly with the increase in laser power while it varied linearly with the scan speed. A proper combination, however, led to fully dense samples. The study reveals an optimum condition in terms of laser power and scan speed that can be adopted to fabricate high-density Inconel 718 parts using laser powder bed fusion–based additive manufacturing process.

Femtosecond-laser-written Ho:KGd(WO4)2 waveguide laser at 2.1 μm.

We report on efficient laser operation of the first holmium monoclinic double tungstate waveguide laser fabricated by femtosecond direct laser writing. A depressed-index buried channel waveguide with a 60μm diameter circular cladding was inscribed in 5at.% Ho3+:KGd(WO4)2. It was characterized by confocal microscopy and μ-Raman and μ-luminescence spectroscopy, indicating well-preserved crystallinity of its core. Pumped by a thulium bulk laser, the holmium waveguide laser generated 212mW at 2055nm with a slope efficiency of 67.2%. The waveguide propagation losses were 0.94±0.2 dB/cm.

Few-layer MXene Ti3C2Tx (T = F, O, or OH) saturable absorber for visible bulk laser

The novel two-dimensional MXenes have been investigated in the photonics field in areas such as broadband nonlinearity, pulse laser generation and passive photonic diode, and so on. In this contribution, the nonlinear optical response at the visible band and the demand pulse laser generation based on MXenes was initially realized. The few-layer MXene Ti3C2Tx was fabricated and utilized as a saturable absorber (SA) to realize passive Q-switched visible bulk laser covering the spectral range of orange (607 nm), red (639 nm), and deep red (721 nm). At the three wavelength, the maximum average output powers and the shortest pulse widths were (111 mW, 426 ns) for 607 nm, (150 mW, 264 ns) for 639 nm, (115 mW, 328 ns) for 721 nm, respectively. Our experimental results indicate the MXene Ti3C2Tx SA could be an efficient and promising optical modulator in the visible domain.

Bismuth quantum dots as an optical saturable absorber for a 1.3 μm Q-switched solid-state laser.

Two-dimensional bismuth has attracted extensive attention for its unique properties, such as a moderate bandgap, high carrier mobility, and high stability. In this work, a uniform bismuth quantum dots saturable absorber (BiQDs-SA) was successfully fabricated by the liquid-phase exfoliation method. It was successfully employed in a passively Q-switched bulk laser operating at the telecommunication wavelength of 1.3μm. The as-fabricated BiQDs-SA-based 1.3μm Q-switched laser not only exhibits low timing jitter but also shows long-term stability for several days. The maximum average output power of 125mW was obtained with the shortest pulse width of 510ns and repetition rate of 135kHz, corresponding to single-pulse energy and pulse peak power of 0.9μJ and 1.8W, respectively. The results indicate that BiQDs-SA is a potential optical modulator for passively Q-switched solid-state lasers.

Growth, spectroscopy and high power laser operation of Yb:YAl3(BO3)4 crystal: Continuous-wave, mode-locking and chirped pulse regenerative amplification

We report on growth, spectroscopy and continuous-wave, mode-locking lasing and chirped pulse regenerative amplification of Yb:YAl3(BO3)4 (Yb:YAB) crystal. Efficient CW laser operation with 9.2 W output power, 46% optical-to-optical and 74% slope efficiencies was demonstrated. Efficient SESAM mode-locked Yb:YAB bulk laser was demonstrated for σ-polarization with 4 W average output power at 70 MHz pulse repetition frequency (PRF) and 195-fs pulse duration resulting in the pulse energy of 57 nJ and pulse peak power of 0.3 MW. Optical-to-optical efficiency of 27% in mode-locked regime is demonstrated. Chirped pulse regenerative amplifier based on Yb:YAB crystal demonstrated with maximum output power of 4.6 W (6 W of chirped pulses and optical-to-optical efficiency of 25%) and 695 fs pulse duration at 100 kHz PRF for the first time to the best of our knowledge.

MoSSe Saturable Absorber-Based High-Power Passively Q-Switched <inline-formula> <tex-math notation="LaTeX">$2.0~\mu$ </tex-math> </inline-formula>m Bulk Laser

A ternary transitional metal dichalcogenides alloy material, molybdenum sulphoselenide (MoSSe), has been successfully fabricated and used as a saturable absorber (SA) for a passively Q-switched (PQS) Tm:YAP bulk laser operating at $2.0~\mu \text{m}$ for the first time, to best of our knowledge. The open aperture Z-scan method was used to characterize the saturable absorption properties of the prepared MoSSe SA. The maximum average output power and pulse repetition rate, shortest pulse width, highest single pulse energy, and highest pulse peak power of this laser were 2.26 W, 95 kHz, 303 ns, $24.2~\mu \text{J}$ , and 80 W, respectively. The results are distinguished from other two-dimensional materials-based $2.0~\mu \text{m}$ PQS lasers, indicating that MoSSe could be a promising material for generating high power and short pulse width lasers in the $2.0~\mu \text{m}$ spectral range.

Passively <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math> </inline-formula>-Switched 2.95-<inline-formula> <tex-math notation="LaTeX">$\mu$ </tex-math> </inline-formula>m Bulk Laser Based on Rhenium Disulfide as Saturable Absorber

Rhenium disulfide (ReS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), one of the typical representatives of 2D layered transition metals dichalcogenide materials, has attracted widespread attention for its optical modulation properties in lasers. In this letter, a high-quality ReS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanosheet film-based saturable absorber (SA) was successfully prepared by a liquid phase exfoliation method and employed into a passively <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -switched Ho,Pr:LiLuF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> bulk laser operating at 2.95 μm. The maximum output power of 103 mW was obtained with the shortest pulse duration of 676 ns and a repetition rate of 91.5 kHz, corresponding to the single pulse energy of 1.13 μJ and a pulse peak power of 1.67 W, respectively. The results indicate that ReS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is a promising SA for mid-infrared pulse generation.

Alpha-phase indium selenide saturable absorber for a femtosecond all-solid-state laser.

We successfully fabricated the high-quality few-layered α-In2Se3 and investigated its carrier dynamics and nonlinear optical absorption properties by pump-probe and open-aperture Z-scan technologies. Intra- and inter-band relaxation times were determined to be 7.2ps and 270ps, respectively, and the effective nonlinear absorption coefficient was measured as βeff=-3.9×103 cm/GW (1064nm). Based on α-In2Se3 saturable absorber, a continuous-wave mode-locking operation was realized. Pulse duration, repetition rate, and maximum output power were measured to be 352fs, 42.4MHz, and 0.56W, corresponding to pulse energy of 13.2nJ and peak power of 37.5kW. To the best of our knowledge, this is the first demonstration of non-transition metal chalcogenides applied in ultrafast all-solid-state bulk lasers. This work well verified that α-In2Se3 should be a promising optical modulator candidate for all-solid-state lasers.

Ternary chalcogenide Ta2NiS5 as a saturable absorber for a 1.9 μm passively Q-switched bulk laser.

In this Letter, a high-quality saturable absorber (SA) based on a multilayered two-dimensional ternary chalcogenide Ta2NiS5 with a narrow bandgap, has been successfully fabricated and used as a SA in a 1.9μm spectral region. The nonlinear saturable absorption properties of the as-prepared SA have been investigated by using an open-aperture Z-scan method. A passively Q-switched all-solid-state laser operating at 1.9μm has been realized with the Ta2NiS5 SA. The maximum average output power, shortest pulse width, pulse energy, and pulse peak power from the passively Q-switched (PQS) laser are 1.1W, 313ns, 22.0μJ, and 71.0W, respectively. This is the first demonstration of the saturable absorption property of Ta2NiS5, to the best of our knowledge. The results indicate well the promising potential of Ta2NiS5 as a broadband SA in realizing pulsed mid-infrared lasers with high performance.