In a laser, the control of its spectral emission depends on the physical dimensions of the optical resonator, restricting it to a set of discrete cavity modes at specific frequencies1-4. Without modifying the optical cavity, this results in substantial gaps in the obtainable laser emission spectrum, as well as a fixed repetition rate, limiting the device's usability in various experiments and applications where a considerable degree of tunability is required in the spectral or temporal domain. Here we overcome this fundamental limit by demonstrating a monolithic semiconductor laser5-7 with a continuously tunable repetition rate from 4 GHz up to 16 GHz, by using a microwave driving signal that induces a spatiotemporal gain modulation along the entire laser cavity8,9, generating intracavity mode-locked pulses10-13 with a continuously tunable group velocity14. At the output, frequency combs15,16 with continuously tunable mode spacings are generated in the frequency domain, and coherent pulse trains with continuously tunable repetition rates are generated in the time domain17. Our results pave the way for fully tunable chip-scale lasers and frequency combs, which will be advantageous for use in a diverse variety of fields, from fundamental studies to applications such as high-resolution and dual-comb spectroscopy18,19.

Synchronized generation of ultranarrow superradiant lasers with stable frequency

This paper describes two front-end architectures developed in a 28 nm CMOS process for the readout of pixel detectors in future high-energy physics (HEP) colliders and advanced X-ray imaging instrumentation. The front-end channels have been developed in the framework of the PiHEX project, funded by the Italian Ministry of University and Research. PiHEX aims to improve the state of the art of pixel readout chip technology in high-luminosity colliders and X-ray imagers in the next generation of free electron lasers (FELs) by developing, in 28 nm CMOS technology, the fundamental microelectronic building blocks for pixel readout chips. Such blocks, also implementing innovative circuit ideas, will enable, in future applications, the integration of large-scale readout chips, meeting a set of challenging requirements, such as high spatial resolution, high signal-to-noise ratio, very wide dynamic range and the capability to withstand unprecedented radiation levels. Two different front-end channels were designed, integrated into two prototype chips, and tested. One architecture, featuring a pixel size of 25 µm × 100 µm, was optimized for tracking applications in high-energy physics experiments, like the ones that take place at CERN in the high-luminosity upgrade of the Large Hadron Collider (LHC), while the second one, featuring a pixel size of 110 µm × 55 µm, was devised for X-ray imaging applications in FELs.

Review on recent dark pulse generation in fiber lasers using real and artificial saturable absorber

Frequency comb generation in mid-infrared interband cascade lasers (ICLs) promises to lead to rapid and low-power-consumption chemical sensing of multiple species or broadband lines in the 3-5 μm atmospheric window. We present a complete electron-wavevector-resolved model of the ICL frequency combs based on the Maxwell-Bloch formalism that intrinsically includes the group velocity dispersion (GVD) from the active core. Using a version of this model validated against the available experimental data, we provide a resolution of several longstanding puzzles in this field. We find that the presence of a fast gain component due to the transfer of electrons from the electron injector reservoir does not preclude the generation of pulses, provided the recovery time of the saturable absorber (SA) section of the two-section devices is sufficiently short. However, the generation of single pulses and phase-locked AM combs appears difficult in the conventional design because of the accumulation of holes over successive round trips. A modified design with the reduced density of states in the hole injector is proposed to overcome this problem. Detailed simulations as a function of the injection current density, SA length and lifetime, waveguide GVD, and other parameters are presented in order to guide the future experimental implementation.

The signal-to-noise ratio and application of traditional chaotic lasers in phase interferometric scenarios are fundamentally limited by their intrinsic large amplitude fluctuations. This paper proposes and demonstrates a robust method for generating an intensity-stabilized phase chaos laser (PCL) through the controlled optical injection of a chaotic master laser into a slave distributed feedback laser. The PCL is theoretically governed by the interplay between the phase perturbation and intensity stabilization. The operational window is experimentally verified with a 6 times threshold driving current of the slave laser to leverage gain saturation for amplitude stabilization, an injection strength of 2.4% to 3.2% for efficient energy transfer, and a frequency detuning of -0.63 GHz to 3.75 GHz to facilitate nonlinear phase locking. Experiments reveal a dramatically suppressed amplitude fluctuation of 5.4 times reduction in peak-to-peak value, a broadband optical spectrum of around 8.7 GHz linewidth, and a correlation dimension of 4.86. This work provides a comprehensive framework for mastering PCL, paving the avenue for its high-precision phase-correlation applications.

ABSTRACT Ultraviolet (UV) nonlinear optical (NLO) crystals with excellent performance are indispensable for advancing high‐precision laser technologies. Anionic groups directly govern the key optical properties including second‐harmonic generation (SHG) response, birefringence, and phase‐matching capability. The [B 3 O 7 ] 5− unit is a classic NLO‐active building block, but its inherent structural limitations (e.g., non‐uniform arrangement in parent crystals) often lead to insufficient birefringence and restricted short‐wavelength phase‐matching potential. Herein, we proposed a synergistic fluorination and organic modification strategy to tailor the [B 3 O 7 ] 5− group, successfully designing and synthesizing two novel magnesium fluoroborate malonate compounds: Mg(BF 2 C 3 O 4 H 2 ) 2 (H 2 O) 2 (MgBCOFH‐1) and Mg(BF 2 C 3 O 4 H 2 ) 2 C 3 O 4 H 4 (H 2 O) 2 (MgBCOFH‐2). Both compounds feature an unprecedented [BF 2 C 3 O 4 H 2 ] − building unit derived from the structural evolution of [B 3 O 7 ] 5− . Notably, MgBCOFH‐1 and MgBCOFH‐2 exhibit enhanced birefringence values of 0.100 and 0.073 @ 546 nm, respectively, significantly surpassing that of the parent [B 3 O 7 ]‐based LiB 3 O 5 (LBO, 0.042 @ 546 nm). More importantly, MgBCOFH‐2 achieves a phase‐matching wavelength of 223 nm (a 54 nm blue‐shift relative to LBO) alongside a moderate SHG intensity (∼1 × KDP @ 1064 nm), making it a promising candidate for a fourth‐harmonic UV laser generation. This work establishes a rational structural modification paradigm for upgrading conventional NLO‐active building blocks and provides insights into the development of high‐performance short‐wavelength UV NLO crystals.

Electrically controlled laser generation in a photonic crystal - liquid crystal - metal microcavity

We demonstrate theoretically the 3.5 μm laser generation based on Tm-assisted self-generated 1980 nm laser side-pumping. The gain medium is a double-clad fluoride fiber with a Tm-doped inner cladding and an Er-doped core. A 793 nm laser diode (LD) pumps Tm ions in the inner cladding to generate a 1980 nm laser, replacing the dedicated external 1980 nm fiber pump source. Combined with a 980 nm LD, Er ions in the core are enabled to generate a 3.5 μm laser. When pumped with sufficient power at 980 nm and a fixed 20 W power at 793 nm, and given a core absorption of 1 dB/m at 1980 nm, the output power of the 3.5 μm laser remains ∼4.9 W in different Er-doped concentrations. Compared with the traditional method, this approach achieves more uniform population inversion along the fiber and a slightly higher 1980 nm to 3.5 μm laser conversion efficiency. This research represents a novel method for simplifying 3.5 μm laser systems and could theoretically improve power scaling via cladding pumping.

We demonstrated a stable dual-wavelength Q-switched fiber laser using a Ti3Al(C0.5, N0.5)2-PVA saturable absorber (SA) deposited on a D-shaped fiber, generating pulses at 1531.36 and 1558.38 nm. The fabricated SA exhibited a modulation depth of 19.6% and a saturation intensity of 0.07 MW/cm². Integrated into the laser cavity, the SA enabled Q-switching over a pump power range of 38–75 mW, with repetition rates increasing from 35.3 kHz to 51.9 kHz and pulse widths narrowing from 6.58 µs to 3.57 µs. A high signal-to-noise ratio of 50 dB confirmed pulse stability. The laser achieved a maximum output power of 5.7 mW and pulse energy of 84.75 nJ. These results highlight Ti3Al(C0.5, N0.5)2 as a promising SA for compact, efficient pulsed fiber lasers operating around 1.55 µm.

. In this article, we will develop linear and nonlinear filtering methods for a large class of nonlinear wave equations that arise in applications such as quantum dynamics and laser generation and propagation in a unified framework. We consider both stochastic calculus and white noise filtering methods and derive measure-valued evolution equations for the nonlinear filter and prove existence and uniqueness theorems for the solutions. We will also study first-order approximations to these measure-valued evolutions by linearizing the wave equations and characterize the filter dynamics in terms of infinite-dimensional operator Riccati equations and establish solvability theorems.

This study investigates the influence of capillary inner diameter on the relative intensity of 69.8 nm laser emission under a main pulse current of 19 kA. Laser output at 69.8 nm was achieved for capillaries with inner diameters of 2.5, 3.0, and 3.2 mm, with the strongest emission observed at 3.0 mm. This work represents the first demonstration of a 69.8 nm laser generated by capillary discharge at a main pulse current other than 12 kA. The relationship between initial gas pressure and laser intensity was experimentally determined for each capillary diameter. The optimal initial pressures for 2.5, 3.0, and 3.2 mm capillaries were 21, 18, and 16 Pa, respectively. As the inner diameter increased, the pressure range for laser generation shifted toward lower values, with the widest operating range observed for the 3.0 mm capillary. No 69.8 nm laser emission was detected for capillaries with inner diameters of 3.5-5.6 mm, indicating that larger diameters are unfavorable for lasing. Theoretical analysis, consistent with experimental conditions, suggests that effective 69.8 nm laser generation occurs at electron temperatures of 113-145 eV and electron densities of (4.4 × 1017) - (1.3 × 1018) cm-3. These plasma parameter ranges provide valuable guidance for realizing 69.8 nm laser emission in future experiments.

A high-power, narrow-linewidth, continuous-wave 355 nm laser based on single-pass third-harmonic generation of a fiber laser in two LBO crystals is presented. Both type I and type II critical phase-matching in LBO crystals was investigated for the sum-frequency generation stage. A maximum output power of 5 W with a root-mean-square power stability of 0.73% was achieved by using a type-I critical PM LBO crystal, with a single-pass conversion efficiency of 1.7% from 1064 nm to 355 nm. The relative intensity noise of the 355 nm laser was below -110 dB/Hz in the frequency range above 200 Hz. Such a single-pass THG laser system, with its compact architecture and robustness, has great potential for applications in semiconductor manufacturing and inspection.

Polyaniline-Enabled Mode-Locking for Supercontinuum Generation in an Erbium-Doped Fiber Laser

A high-average-power narrow linewidth coherent nanosecond (ns) pulsed laser operating in a broad wavelength range is a crucial source for optical sensors, spectroscopy, lidar, generation of deep-ultraviolet lasers, and many more applications. Here, we propose an innovative technical approach for the generation of high-average-power single-frequency ns laser tunable from 766 nm to 775 nm and 1535 to 1570 nm based on a coherent optical parametric generator (OPG), utilizing a single-frequency ns green laser as the pump source in conjunction with a continuous-wave tunable 1.5 µm single-frequency laser as the seeding source. The OPG is based on a non-critical phase-matching LBO crystal, pumped by an 84 W 515 nm 6.10 ns 100 kHz pulsed single-frequency laser, second harmonic of a home-made 135 W fiber-solid hybrid master-oscillator power amplification system, and seeded by a 1.5 µm single-frequency fiber laser tunable from 1535-1570 nm. Consequently, the OPG achieves high-power single-frequency ns pulse output tunable from 766 nm to 775 nm and 1535 nm to 1570 nm, as signal and idler, respectively. At 775 nm, the signal laser obtains an average power of 33.76 W, corresponding to a conversion efficiency of 40.19% with a pulse width of 5.16 ns and a peak power of 65.42 kW, while maintaining excellent beam quality (Mx2=1.26, My2=1.23). In addition, the idler laser reaches a maximum average power of 16.00 W with a pulse width of 5.00 ns and a peak power of 32.00 kW at 1535 nm. To the best of our knowledge, this research realizes the highest average power of dual-band tunable single-frequency ns pulse laser output based on a seeded LBO-OPG.

Pure-quartic solitons (PQSs), as an emerging branch of the soliton family, have flourished and achieved significant progress in near-infrared fiber laser systems. Extending their generation to the mid-infrared (mid-IR) region and revealing associated nonlinear dynamics are of great interest. Herein, we numerically investigate the generation and dynamic behaviors of mid-IR PQSs at 3 µm in a passively mode-locked Dy 3+ -doped fluoride fiber laser. The simulation results demonstrate that mid-IR PQSs, in contrast to their near-IR counterparts, can be generated under a negative fourth-order net cavity dispersion of significantly smaller magnitude (∣ β 4 ∣ L <4.5×10 −3 ps 4 ). Furthermore, under the fourth-order net cavity dispersion β 4 L =−1.8×10 −3 ps 4 , annihilation and crawling dynamics of mid-IR PQS molecules are observed by selecting the appropriate saturable energy of the Dy 3+ -doped fluoride fiber. These findings offer critical theoretical insights for the generation and manipulation of mid-IR PQS mode-locked fiber lasers.

The Yb:CaYAlO4 (Yb:CALYO) crystal, which boasts a very broad emission spectrum and moderate thermal conductivity, is highly promising for the generation of high-power femtosecond lasers with short pulse durations. However, research into Yb:CALYO-based high-power femtosecond amplifiers has been limited. Here, we report on a Yb:CALYO-based dual-crystal regenerative amplifier capable of delivering high average power and high pulse energy. The maximum single-pulse energy of 6.5 mJ was achieved at a 5-kHz repetition rate, corresponding to an average power of 32.5 W. Additionally, the maximum average power of 65.2 W was achieved at a 50-kHz repetition rate, corresponding to a single-pulse energy of 1.3 mJ. In both instances, the pulse durations were shorter than 200 fs, accompanied by good power stability. To the best of our knowledge, these results represent the highest average power and pulse energy ever achieved from a Yb:CALYO-based femtosecond amplifier, indicating that Yb:CALYO is an excellent candidate for high-power femtosecond lasers with both high energy and short pulse duration. It is believed that it could develop femtosecond lasers at the 10-mJ level with average power exceeding 100 W and sub-200 fs pulse duration.

The unique characteristics of 2-5 μm mid-infrared supercontinuum (SC) lasers, making them ideal tools for a wide range of applications. However, conventional technical approaches face significant challenges in generating high-power mid-infrared SC lasers beyond the 4 μm band through a single mid-infrared fiber, which substantially limits the practical applications of mid-infrared SC light sources. Precise tapering enables flexible manipulation of fiber nonlinearity and dispersion, optimizing both output power and spectral bandwidth for enhanced SC generation. This paper presents a 10.08 W all-fiber mid-infrared SC light source based on tapered fluorotellurite fiber. Compared to its untapered counterpart, the tapered fluorotellurite fiber achieved a 1500 nm long-wavelength extension with a spectral range of 2-4.8 μm at 10.08 W. Notably, the power fraction beyond 3000 nm increased sevenfold, from 4% to 30%. To the best of our knowledge, this is the first report of an all-fiber high-power mid-infrared SC source with the widest spectral range based on tapered fluorotellurite fiber.

Mechanisms of THz radiation generation in multi-color laser–plasma interactions: a review across diverse media

Enhancement of Vacuum-Ultraviolet Laser Generation through Near-Threshold Harmonics Driven by a Few-Cycle Two-Color Laser Field