We report a high-power, high-efficiency continuous-wave Tm:KY(WO4)(2) (Tm:KYW) laser based on multimode in-band diode pumping at 1720 nm. In-band pumping reduces the quantum defect compared to conventional 800-nm pumping, enabling efficient high-power operation. We demonstrate up to 4.55 W of output power near 1.94 mu m with a slope efficiency of 83% with respect to absorbed pump power, approaching the quantum-defect limit. The laser provides smooth wavelength tunability from 1839 to 2100 nm and maintains near-diffraction-limited transverse beam quality across the full operating range. These results indicate that multimode in-band pumping of Tm:KYW is a simple and compact route to efficient, broadband, high-power sources in the 1.9-2.0 mu m region, providing a practical basis for future high-power Q-switched and mode-locked systems.

We report the first Kerr-lens mode-locked Tm:KYW bulk laser oscillator. Using compact multimode diode in-band pumping, also for the first time in a mode-locked Tm-based oscillator, we demonstrate a threefold increase in average power compared with previously reported Tm- and Tm,Ho-based bulk oscillators in the sub-150 fs regime operating at comparable pulse durations, while maintaining high efficiencies. Two cavity configurations operating at a repetition rate of 165 MHz are demonstrated. In the first configuration optimized for average-power scaling, the oscillator delivers 135 fs pulses with 2.05 W of average output power, corresponding to 48% optical-to-optical efficiency and 81 kW peak power. The second configuration, optimized for short pulses, generates 86 fs pulses with 1.1 W of average power, 42% optical-to-optical efficiency, and 68.2 kW peak power. These results establish Tm:KYW combined with multimode diode in-band pumping as a highly promising platform for compact, cost-efficient, and power-scalable femtosecond bulk oscillators in the 1.9–2.0 μm spectral range.

We report on the noise characterization of a free-running ring quantum cascade laser resonator emitting a single frequency mode around 7.7 mu m. Using a gas cell filled with N 2O as a frequency-to-voltage discriminator, we measured the frequency noise power spectral density of the laser from which we extracted its linewidth. The results show a full width at half maximum close to 50 kHz at 1 s integration time, which represents at least a sixfold improvement compared to state-of-the-art quantum cascade lasers operating in a spectral region above 7 mu m. We also demonstrate that such lasers can be efficiently used for frequency modulation spectroscopy, which opens up new possibilities for high resolution metrology and spectroscopic applications in the mid-infrared.

We report on the development of low-loss ion-beam-sputtered (IBS) mid-infrared coatings for hybrid supermirrors. Two highly reflective designs were realized: HR1, a four-period a-Si/SiO 2 DBR with an Al 2 O 3 bonding layer, and HR2, a six-period a-Si/Ta 2 O 5 DBR with an a-Si terminating layer for bonding. Combined with a GaAs/AlGaAs crystalline mirror, HR2-based hybrids yielded a total loss of 9.3 ppm and excess loss of 6.8 ppm at 4.45 µm, with cavity finesse up to 396,000. We used IBS-deposited a-Si directly as a bonding layer, for the first time, to our knowledge, verified its sub-angstrom roughness, and demonstrated excellent optical performance. This establishes a clear path toward scalable coatings for longer mid-infrared wavelengths, building on prior results in Nat. Commun. 14 , 7846 ( 2023 ). NCAOBW 2041-1723 10.1038/s41467-023-43367-z

Highly reflective (HR) optical coatings for the mid-infrared (MIR) spectral region are a vital component for a wide variety of applications, especially cavity-enhanced spectroscopy methods [1], [2]. However, HR coatings deposited by physical vapor deposition techniques often suffer from high excess loss $S$+$A$ (scatter/absorption) in the MIR. Recently, monocrystalline substrate-transferred supermirrors have emerged as an excellent alternative in the MIR region [1]–[3]: the latest 44.5-period GaAs/AlGaAs distributed Bragg reflectors (DBR) grown via molecular beam epitaxy (MBE) yielded extremely low S+A = 4.27 ppm and total loss 1-R = 13.6 ppm (two-mirror cavity finesse $F$ = 231000) at a center wavelength (CWL) $\lambda_{0}=4.45\ \mu \mathrm{m}$[1]. Still, the low refractive index contrast of GaAs/AlGaAs requires a high number of quarter-wave layers for optimal reflectivity R, leading to thick coatings. This impedes scaling of MBE-grown DBRs to CWLs well above $5\ \mu \mathrm{m}$ due to manufacturing constraints.

We report details on the design, manufacturing, and characterization of low-loss ion-beam-sputtered mulitlayers used for amorphous-crystalline hybrid supermirrors for mid-infrared applications, including details on anti-reflective and highly reflective coatings.

In this article, we present an alternative sampling approach for continuous-wave terahertz homodyne systems that overcomes limitations regarding the measurement of dispersive samples of currently used techniques. The wavelength-dependent phase-delay mirrors, which were developed for this work, induce a frequency-dependent phase shift of up to pi/2. This technique allows sampling of the THz-field, by tuning the laser sources in such a way that a constant frequency difference is maintained and the center frequency is shifted. In our configuration, the phase shift between transmitter and receiver arms depends only on the center frequency of the lasers. This allows for replacing the movement of a delay stage with variation of the center frequency to capture a THz trace. Consequently, measurements are not constrained by the speed of the delay line anymore. Furthermore, this phase shift is unaffected by differences in path length within the setup and does not require phase modulators. Prior simulations show that these mirrors achieve a phase shift up to pi in the C-band for a difference frequency of 280 GHz, which could be confirmed by our measurements. We successfully demonstrated the first application by measuring sample thickness.

Here we apply cavity ring-down spectroscopy to measure the intensity of a rotational-vibrational transition within the fundamental (1-0) vibrational band of carbon monoxide (CO). Laser measurements were made at a wavenumber near 2206 cm-1 on a sample of CO-in-air with an amount fraction of chi CO = 77.6 nmol mol-1. High-precision cavity ring-down spectra were acquired using hybrid amorphous-crystalline mirrors to form the optical resonator and by application of simple and robust laser scanning and control techniques. With a relative combined standard uncertainty of uS = 0.6 %, we report the R17 line intensity for the fundamental (1-0) vibrational band of 12C16O to be S = 1.028 x 10-19 cm-1 molecule-1 (isotopologue abundance, chi iso = 100 %; temperature, T = 296 K), a value which differs from HITRAN2020 by a relative amount of 2.2 %.

Optical injection locking of the repetition frequency of a quantum cascade laser frequency comb is demonstrated using intensity modulated near-infrared light at 1.55 µm, illuminating the front facet of the laser. Compared to the traditional electrical modulation approach, the introduced technique presents benefits from several perspectives, such as the availability of mature and high bandwidth equipment in the near-infrared, circumvents the need for dedicated electronic components for the quantum cascade laser, and allows a direct link between the near and mid-infrared for amplitude to frequency modulation. We show that this stabilization scheme, used with moderate near-infrared power of a few milliwatts, allows for a strong reduction of the frequency noise. We also perform a full characterization of the mechanism and provide evidence that the locking range follows Adler’s law. A comparison of our results with those in recent literature indicates that the optical approach leads to better performance compared to the traditional method, which we expect to benefit mid-infrared spectroscopy and metrological applications.

Optical parametric amplification is one of the most flexible approaches for generating coherent light at long wavelengths, but typical implementations require prohibitively large pump pulse energies to realize useful amounts of gain. In this work, we experimentally demonstrate an approach to optical parametric amplification in which an interplay between parametric gain and symmetric temporal walk-off confines the non-degenerate signal and idler to form a three-wave soliton. Gain-trapped solitons propagate stably over arbitrarily long interaction lengths, which reduces the energy required for high-gain operation by orders of magnitude. The devices demonstrated here realize large parametric gains (>70dB) with only picojoules of pump pulse energy in a 5-mm-long thin-film lithium niobate on sapphire nanowaveguide. In addition, we observe an array of desirable features including high conversion efficiencies (>50%), wide tuning ranges (>100nm), and broad spectral bandwidths (>180nm 3 dB for the 3200-nm idler). When combined with the dispersion engineering available in tightly confining nanowaveguides, this approach enables high-gain optical parametric amplifiers operating at any wavelength.

We investigate power scaling with a signal singly-resonant OPO pumped with a 125 MHz Yb:fiber CPA. We achieve an average power of 10.3 W at 3.1 µm with a free-running power stability of 0.84%.

We simulated the time-dependent temperature profiles inside a blue diode pumped Ti:Sapphire (Ti:Sa) laser amplifier for several different pulsed pump configurations using a discrete element method, including temperature-dependent thermal conductivity and specific heat capacity of Ti:Sa crystals. Furthermore, we calculated the resulting focal length of the thermal lenses using the optical path differences through the crystal.

We demonstrate ultraviolet-to-mid-infrared supercontinuum generation driven inside thin-film lithium niobate on sapphire nanowaveguides. With only 40 pJ from pump pulses centered around 2100 nm, we record a broad spectrum spanning from 380 to 2700 nm.

Resonant enhancement inside an optical cavity has been a wide-spread approach to increase efficiency of nonlinear optical conversion processes while reducing the demands on the driving laser power. This concept has been particularly important for high harmonic generation XUV sources, where passive femtosecond enhancement cavities allowed significant increase in repetition rates required for applications in photoelectron spectroscopy, XUV frequency comb spectroscopy, including the recent endeavor of thorium nuclear clock development. In addition to passive cavities, it has been shown that comparable driving conditions can be achieved inside mode-locked thin-disk laser oscillators, offering a simplified single-stage alternative. This approach is less sensitive to losses thanks to the presence of gain inside the cavity and should thus allow higher conversion efficiencies through tolerating higher intensity in the gas target. Here, we show that the intra-oscillator approach can indeed surpass the much more mature technology of passive enhancement cavities in terms of XUV flux, even reaching comparable values to single-pass sources based on chirped-pulse fiber amplifier lasers. Our system operates at 17 MHz repetition rate generating photon energies between 60 eV and 100 eV. Importantly, this covers the highly attractive wavelength for the silicon industry of 13.5 nm at which our source delivers 60 nW of outcoupled average power per harmonic order.

We present a multi-mode diode-pumped Yb:CALGO laser oscillator based on cross-polarization pumping. Using this method, we demonstrate 22-fs pulses at 0.3 W, which is the shortest duration for any Yb- based bulk laser oscillator utilizing multimode-diode pumping.

Within the domain of optical frequency comb systems operating in the mid-infrared region, extensive exploration has been undertaken regarding critical parameters, such as stabilization, coherence, or spectral tunability. Despite this, certain essential parameters remain inadequately addressed, particularly concerning light source stability at high average powers. This study explores stability limitations of an optical parametric oscillator system when scaling to several watts of average power of the idler. Notably, the highest average power reported in the 3-5 mu m region, reaching 10.3 W for the idler output at 3.1 mu m, is achieved. Additionally, we analyze the phase noise and beam quality of both idler and signal beams and identify the onset of higher order modes as limiting for stability at high-power operation. Finally, we estimate the free-running optical linewidth of our idler beam to be similar to 300 kHz, undermining the high passive temporal stability of our source. These findings represent a significant advancement toward the realization of highly stable high-power optical frequency combs in the mid-infrared region, thereby facilitating applications previously constrained by light source average powers and quality limitations. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/4.0/).

We present an optical parametric oscillator synchronously-pumped with a 125 MHz Yb:fiber chirped pulse amplifier and achieve a record-high average power of 10.3 W at 3.1 µm with a free-running power stability of 0.84%.

For trace gas sensing and precision spectroscopy, optical cavities incorporating low-loss mirrors are indispensable for path length and optical intensity enhancement. Optical interference coatings in the visible and near-infrared (NIR) spectral regions have achieved total optical losses below 2 parts per million (ppm), enabling a cavity finesse in excess of 1 million. However, such advancements have been lacking in the mid-infrared (MIR), despite substantial scientific interest. Here, we demonstrate a significant breakthrough in high-performance MIR mirrors, reporting substrate-transferred single-crystal interference coatings capable of cavity finesse values from 200 000 to 400 000 near 4.5 µm, with excess optical losses (scatter and absorption) below 5 ppm. In a first proof-of-concept demonstration, we achieve the lowest noise-equivalent absorption in a linear cavity ring-down spectrometer normalized by cavity length. This substantial improvement in performance will unlock a rich variety of MIR applications for atmospheric transport and environmental sciences, detection of fugitive emissions, process gas monitoring, breath-gas analysis, and verification of biogenic fuels and plastics.

In THz homodyne systems, optical delay lines are the key to time-resolved measurements but they come with a high cost and complexity. They also limit the application of the system in industrial environment, due to their sensitivity to vibrations. Another important point is the scanning speed, for which the mechanical delay line sets severe limitations. Frequency scanning-based systems need a change in THz frequency to recover phase information. Furthermore, there is a tradeoff between phase sensitivity and necessary tuning range. This tradeoff is based on the difference in the length of transmitter and receiver arm in the setup. With our approach, we can introduce a controllable phase shift at 280 GHz by frequency tuning of both lasers. For that purpose, chirped mirrors were designed and introduced into a standard continuous wave Terahertz homodyne system, in order to induce a variable phase shift. In our chirped mirror-based configuration, the phase shift between both optical modes depends on the center frequency of the lasers. Thus, moving the delay stage can be replaced by variation of the center frequency in order to record a THz trace. This means that the measurements are no longer limited by the speed of the delay line. This phase shift is independent of the path length difference in the setup and does not need phase modulators. Simulations show, that these mirrors may achieve a phase shift up to pi inside the C-Band for a difference frequency of 280 GHz. To confirm the calculated behavior of the chirped mirrors, initial characterization measurements were performed. We modified an existing delay stage-based THz system to include the chirped mirrors in front of the receiver. This enables the direct comparison while keeping all other parameters constant.