Ultrafast solid-state glass lasers are frequently mode-locked using a semiconductor saturable absorber mirror (SESAM), which can provide reliable laser self-start and stable mode-locked operation. However, state-of-the-art GaAs-based SESAMs for the 1.55 µm wavelength range require highly strained InGaAs quantum well absorbers with a lattice-mismatch of ≥ 2% relative to the GaAs substrate, which leads to defect formation, reduced damage threshold, and limited design freedom. Here, we present the first fully strain-free SESAMs for solid-state glass lasers at 1.55 µm wavelength, which overcome these constraints. Our devices are grown on InP with a very low residual lattice-mismatch of < 0.1% and incorporate an iron-doped InGaAs bulk absorber. This enables continuous tunability of the SESAM modulation depth and precise control over the ultrafast SESAM recovery time - an unprecedented degree of design freedom. Furthermore, the SESAM structure combines an anti-resonant design with a highly reflective InAlAs/InGaAlAs bottom DBR and a TiO2/SiO2 top DBR, which results in record-low non-saturable losses for InP-based SESAMs of 0.6% for a modulation depth of 0.6%. With this approach, we demonstrate the first stable continuous-wave mode-locked operation of a solid-state Er,Yb:glass laser using an InP-based SESAM. We achieve 224 fs pulse duration at a maximum output power of 102.5 mW and a 79.1 MHz repetition rate, in combination with excellent noise properties of 0.005% integrated RIN over [100 Hz, 1 MHz] and 3 fs integrated timing jitter over [1 kHz, 1 MHz].

Abstract Two-photon lithography fabricates three-dimensional structures with 100-nanometer resolution; yet its industrial adoption is hindered by poor reproducibility and the need for complex manual tuning processes. While post-fabrication metrology, such as scanning electron microscopy, characterizes final morphologies, it cannot prevent manufacturing errors. Here we show a two-photon lithography platform powered by a single-cavity dual-comb laser that addresses this limitation through real-time correction. During fabrication, one laser comb, after frequency conversion, performs two-photon printing, while the dual-comb system simultaneously performs in-situ phase measurements across the full work field at 360 hertz. By feeding the phase profiles into a dynamic model, the platform automatically modulates printing parameters to correct height errors. We demonstrate this capability through a continuous 14-hour fabrication process to manufacture different millimeter-scale diffractive optical elements with less than 100-nm absolute errors. The resulting devices exhibit superior signal-to-noise ratios, process repeatability, and focus quality. This closed-loop dual-comb platform offers a cost-effective, scalable solution for high-precision, high-yield nanomanufacturing.

Fiber-coupled terahertz (THz) time-domain spectroscopy (TDS) systems often employ photoconductive antennas (PCAs) as THz emitters due to their high IR-to-THz conversion efficiency. However, their THz power has been constrained to about 1 mW, as fiber-based pulse delivery limits the excitation power to under 60 mW at typical fiber laser repetition rates around 100 MHz. Here, we report the first THz TDS setup that overcomes this limitation by operating at an elevated repetition rate of 1 GHz. We show that the conversion efficiency of InGaAs:Rh-based PCAs is preserved at this one-order-of-magnitude higher repetition rate, resulting in a record emitted THz power of 1.58 ± 0.08 mW for fiber-coupled THz emitters. This significant improvement is enabled by an ultrafast dual-comb optical parametric oscillator operating at 1 GHz repetition rate, delivering two trains of 200 fs pulses centered at 1.55 μm wavelength with up to 650 mW average power. Further pulse compression to 86 fs is achieved using a 2.6 m long fiber delivery to the PCAs, combining dispersion-compensating and standard polarization-maintaining fibers. Using this setup, we demonstrate THz TDS utilizing asynchronous optical sampling at a scan rate of 414 Hz with a peak dynamic range of up to 92 dB at 20 GHz frequency resolution, and 79 dB at 1.1 GHz frequency resolution in 113 seconds integration time.

Developing high-brightness, low-noise supercontinuum (SC) sources is critical for a variety of ultrafast photonics applications. A key challenge in achieving low-noise operation is the suppression of incoherent nonlinear effects and the associated noise amplification. All-normal dispersion (ANDi) SC sources exhibit considerably reduced noise levels compared to conventional soliton-based methods, but their previous lowest-noise demonstrations were limited by amplified spontaneous emission from amplified femtosecond pump laser systems, which seeds incoherent nonlinearities and degrades SC quality. Consequently, the ultimate low-noise limits of coherent SC generation have not been demonstrated by experimental results. Here, we report ultra-low noise, shot-noise-limited SC generation by directly driving the SC process with the un-amplified output of a high-power dual-comb Yb:CALGO oscillator centered at 1053 nm. The resulting SC combs each have a spectrum spanning 820–1280 nm (−20 dB), 1.6 W average power, 1.03 GHz repetition rate, and a comb-line power of ≈10 μW. We conduct detailed noise studies of the SC by analyzing various ≈15-nm-wide spectral bands. All bands reach a shot-noise-limited relative intensity noise below −160 dBc/Hz at 100-kHz to few-MHz noise frequencies. Furthermore, the central spectral bands exhibit an unprecedented noise suppression of the pump laser’s technical noise above ≈2 kHz by >20 dB, which agrees with our semiclassical simulations. Finally, we simultaneously couple both combs into a single ANDi fiber to generate a dual-comb SC with highly symmetric spectra and correlated noise properties between the combs. Coherently averaged linear optical sampling measurements on the dual-comb SC exhibit a high signal-to-noise ratio, showcasing its potential for real-time spectroscopic measurements.

We report, to the best of our knowledge, the first demonstration of dual-comb operation from a femtosecond optical parametric oscillator (OPO) at a 1-GHz pulse repetition rate. The singly-resonant OPO is fundamentally synchronously pumped by a high-power low-noise Yb:CaF2 diode-pumped solid-state laser, enabling a compact system design, high parametric gain, and stable uniform pulse trains for both the signal and idler outputs. Dual-comb generation is realized in a spatially multiplexed single-cavity configuration for both the OPO and the pump laser. The center wavelength is tunable from 1415 nm to 1645 nm (signal) and 2960 nm to 4085 nm (idler) with average powers up to 650 mW and 200 mW per comb, respectively. The source delivers on average an instantaneous bandwidth of 2.5 THz, a power-per-combline up to 270 µW in the short-wave infrared and 75 µW in the mid-wave infrared is available. We demonstrate the potential of this source for fast dual-comb spectroscopy by detecting ambient methane (∼2 ppm) at 1645.5 nm over a 41-m path length, achieving a normalized spectral signal-to-noise ratio of 42.0 dB Hz1/2. This measurement was performed without any active stabilization.

In this invited talk we present several milestone results that highlight the abilities of our dual-comb MIXSEL technology in the long-wavelength regime.

We report the first demonstration of dual-comb operation from a femtosecond optical parametric oscillator (OPO) at a 1-GHz pulse repetition rate. The singly-resonant OPO is fundamentally synchronously pumped by a high-power low-noise Yb:CaF2 diode-pumped solid-state laser, enabling a compact system design, high parametric gain, and stable uniform pulse trains for both the signal and idler outputs. Dual-comb generation is realized in a spatially multiplexed single-cavity configuration for both the OPO and the pump laser. The center wavelength is tunable from 1415 nm to 1645 nm (signal) and 2960 nm to 4085 nm (idler) with average powers up to 650 mW and 200 mW per comb, respectively. The source delivers on average an instantaneous bandwidth of 2.5 THz, a power-per-combline up to 270 μW in the short-wave infrared and 75 μW in the mid-wave infrared is available. We demonstrate the potential of this source for fast dual-comb spectroscopy by detecting ambient methane (∼ 2 ppm) at 1645.5 nm over a 41-m path length, achieving a normalized spectral signal-to-noise ratio of 42.0 dB Hz1/2. This measurement was performed without any active stabilization.

We demonstrate a spatially multiplexed dual-comb mode-locked Er:Yb:glass solid-state oscillator at 500 MHz. The laser outputs two coherent pulse trains (~40 mW, 230 fs), enabling high-resolution dual-comb spectroscopy without any stabilization.

We present a coaxial dual-comb LiDAR integrated into a laser micromachining station, enabling in-situ 3D profiling of machined parts with sub-micrometer axial precision, offering a cost-effective solution with high precision capability.

Hyperspectral LiDAR (HSL) enables the simultaneous acquisition of the surface geometry and spectral signatures of remote natural targets, making it valuable for various applications such as material probing, automated point cloud segmentation, and vegetation health monitoring. We present a first proof-of-concept study of a broadband dual-comb HSL system based on a 1-GHz dual-comb supercontinuum (SC). The SC spans from 820 to 1300 nm, generated via coherent spectral broadening of a free-running single-cavity dual-comb oscillator at 1053 nm in a single nonlinear photonic crystal fiber. The HSL system achieves a sub-μm ranging precision on a non-cooperative target at an update rate of 670 Hz. The shot-noise limited electronic dual-comb interferograms furthermore encode the spectral information of the target reflection across the SC bandwidth. This allows the capture of precise 3D point clouds with spectral signatures, unlocking new possibilities for spectrum-based material classification.

Dual-comb ranging has emerged as an effective technology for long-distance metrology, providing absolute distance measurements with high speed, precision, and accuracy. Here, we demonstrate a dual-comb ranging method that utilizes a free-space transceiver unit, enabling dead-zone-free measurements and simultaneous ranging with interchanged comb roles to allow for long-distance measurements, even when the target is moving. It includes a graphics processing unit (GPU)-accelerated algorithm for real-time signal processing and a free-running single-cavity solid-state dual-comb laser with a carrier wavelength λc ≈ 1055 nm, a pulse repetition rate of 1 GHz, and a repetition rate difference of 5.06 kHz. This combination offers a fast update rate and sufficient signal strength to reach a single-shot time-of-flight precision of around 0.1 μm (i.e., <λc/4) on a cooperative target placed at a distance of more than 40 m. The free-running laser is sufficiently stable to use the phase information for interferometric distance measurements, which improves the single-shot precision to <20 nm. To assess the ranging accuracy, we track the motion of the cooperative target when moved over 40 m and compare it to a reference interferometer. The residuals between the two measurements are below 3 μm. These results highlight the potential of this approach for accurate and dead-zone-free long-distance ranging, supporting real-time tracking with nm-level precision.

We present a compact and low-noise singly-resonant femtosecond optical parametric oscillator at 1-GHz repetition rate synchronously-pumped by a 1-GHz Yb:CaF2 solid-state single-cavity dual-comb laser. The OPO's timing jitter integrated from 100 Hz to 10 MHz is 9.7 fs at 1540 nm.

We report 1-GHz watt-level ultra-low noise dual-comb supercontinuum generation in a single birefringent photonic crystal fiber using polarization multiplexing. Both combs originate from the same laser cavity and are broadened to > 450 nm bandwidth.

Passively modelocked, optically pumped semiconductor disk lasers, commonly referred to as VECSELs or MIXSELs, offer a unique combination of wavelength versatility, wafer scalability, high beam quality, and substantial average output power. While V-shaped cavities are typically used for SESAM-modelocked VECSELs, MIXSELs utilize a simplified straight cavity, integrating the saturable absorber into the VECSEL chip. Here, we demonstrate a dual-comb modelocked MIXSEL in the Short-Wave Infrared (SWIR) regime, employing InGaSb quantum well gain and saturable absorber layers. The free-running dual-comb MIXSEL generates distinct microwave comb lines based on a few interferograms, eliminating the need for stabilization. Two distinct repetition rates enable sampling without aliasing while maintaining rapid acquisition times. Moreover, the phase of the heterodyne beat interferograms can be tracked, allowing for the application of coherent averaging algorithms. This breakthrough lays the foundation for dual-comb spectroscopy in the 2-μm regime providing direct access to CO2 spectroscopy.

We investigate terahertz time-domain spectroscopy using a low-noise dual-frequency-comb laser based on a single spatially multiplexed laser cavity. The laser cavity includes a reflective biprism, which enables generation of a pair of modelocked output pulse trains with slightly different repetition rates and highly correlated noise characteristics. These two pulse trains are used to generate the THz waves and detect them by equivalent time sampling. The laser is based on Yb:CALGO, operates at a nominal repetition rate of 1.18 GHz, and produces 110 mW per comb with 77 fs pulses around 1057 nm. We perform THz measurements with Fe-doped photoconductive antennas, operating these devices with gigahertz 1 mu m lasers for the first time, to our knowledge, and obtain THz signal currents approximately as strong as those from reference measurements at 1.55 mu m and 80 MHz. We investigate the influence of the laser's timing noise properties on THz measurements, showing that the laser's timing jitter is quantitatively explained by power-dependent shifts in center wavelength. We demonstrate reduction in noise by simple stabilization of the pump power and show up to 20 dB suppression in noise by the combination of shared pumping and shared cavity architecture. The laser's ultra-low-noise properties enable averaging of the THz waveform for repetition rate differences from 1 kHz to 22 kHz, resulting in a dynamic range of 55 dB when operating at 1 kHz and averaging for 2 s. We show that the obtained dynamic range is competitive and can be well explained by accounting for the measured optical delay range, integration time, as well as the measurement bandwidth dependence of the noise from transimpedance amplification. These results will help enable a new approach to high-resolution THzTDS enabled by low-noise gigahertz dual-comb lasers. (c) 2024 Optica Publishing Group under the terms of the Optica