We demonstrate a quasicontinuous sub-& micro;K strontium source achieved without the use of a high-finesse cavity-locked laser. Our frequency reference is based on a dispersion-optimized, fiber-based frequency comb that enables sub-kHz linewidths. The long-term stability of the comb is defined by an external rf reference: either a 10 MHz rf signal from the Dutch Metrology Institute (VSL) or a tunable rf source whose long-term stability is maintained by monitoring and stabilizing the position of a narrow-line magnetooptical trap (MOT) [Sillus et al., Rev. Sci. Instrum., 92, 033204 (2021); Heizenreder et al., Continuous cloud position spectroscopy using a magneto-optical trap, Phys. Rev. Appl. (2026)]. The comb-stabilized system is benchmarked against a conventional cavity-locked laser and achieves comparable performance in broadband and single-frequency MOTs using the narrow 1S0 -> 3P1 laser-cooling transition. We generate high-flux, sub-& micro;K samples of all three bosonic strontium isotopes and demonstrate quasicontinuous outcoupling from the MOT. These results highlight the system's suitability for compact, robust, and field-deployable continuous cold-atom devices.

Sources for high frequencies in the THz range are of interest in both precision measurements in spectroscopy as well as high carrier frequencies and bandwidth in next-generation communication. Optically generated THz frequencies allow for broad tunability based on telecom technologies. Optical frequency division via an optical frequency comb has the potential to generate ultralow phase-noise THz sources. We present a system that is capable of generating tunable THz frequencies of up to 10 THz at 0.5 THz/s scan rates, phase-locked to a common comb spectrum providing absolute frequency calibration. We show results of combining the photonic source with an electronic receiving system in the waveguide band WR 2.2 (330-500 GHz).

Our research team has achieved a significant milestone by generating pulses with sub-20-attosecond (as) timing jitter from a 200-MHz all-polarization-maintaining (PM) erbium-doped (Er:) nonlinear amplifying loop mirror (NALM) fiber laser. Accurate measurement of these temporal fluctuations was conducted using the balanced optical cross-correlation (BOC) technique. Through comprehensive investigation, we identified the critical parameters responsible for timing jitter, including dispersion and pump power, and validated their impact. The fine-tuning of the contributing factors allowed us to demonstrate an exceptionally low integrated timing jitter of only 15.59 attoseconds, integrated from 10 kHz to 10 MHz. This accomplishment stands as the lowest value ever documented for any free-running mode-locked fiber lasers that are erbium-doped.

Our team reached a remarkable milestone by generating pulses with a timing jitter of less than 20 attoseconds using a 200-MHz all polarisation maintaining (PM) erbium-doped (Er:) nonlinear amplifying loop mirror (NALM) fiber lasers. To precisely quantify these temporal variations, we employed the balanced optical cross-correlation (BOC) technique. Through meticulous investigation, we identified the key parameters responsible for timing jitter, including dispersion, pump energies for oscillators and amplifiers, as well as spectral and temporal pulse half-widths, and empirically validated their influence. This systematic analysis and adjustment of the contributing factors enabled us to showcase an exceptionally low integrated timing jitter of 14.25 attoseconds [10 kHz - 4MHz].

OBJECTIVES:With over 184,000 new cases and more than 99,000 deaths per year, malignancies of the larynx are a global health problem. Currently, a dedicated screening method enabling a direct onsite diagnosis is missing. This can lead to delayed diagnosis and worse outcomes of the patients. An endoscopic optical method enabling a direct distinction between healthy tissue, dysplastic tissue and cancerous tissue would be an ideal tool for the detection of tumors of the upper aerodigestive tract (UADT). Healthy and tumor cells differ significantly in their metabolic state due to the different metabolic pathways they use (more oxidative phosphorylation in healthy cells, more glycolysis in tumor cells). Optical metabolic imaging (OMI) measuring relative intracellular concentration of NAD(P)H and FAD redox pairs could be a promising approach for early tumor detection and differentiation of suspicious mucosal lesions. METHODS:In this study, a specially designed endoscopic two-beam two-photon fluorescence lifetime imaging (FLIM) system was used to perform two-photon two-beam FLIM of NAD(P)H and FAD to image the metabolic state in different tissue samples of the UADT. FLIM data sets of 27 tissue samples from 16 patients were recorded directly after surgery ex vivo in a special tissue culture medium at 37°C on a dedicated microscope using multiphoton excitation. RESULTS:Based on the FLIM measurements of NAD(P)H and FAD, six of the most common indices for the characterization of the cells' metabolism were calculated. Three of them, the ratio of the exponential coefficients (amplitudes) of the short and long lifetime components both for NAD(P)H and FAD (NAD(P)H a1/a2 ratio and FAD a1/a2 ratio) and the fluorescence lifetime redox ratio (FLIRR) enabled differentiation between healthy tissue, benign lesions, dysplastic tissue, and cancer tissue with statistical significance. CONCLUSIONS:We showed by measurements on freshly collected tissue samples that mucosal lesions of the UADT can be differentiated using our newly designed endoscopic FLIM device. In vivo measurements in healthy volunteers were also possible. By means of this technology, differentiation of cancerous, pre-cancerous, and healthy tissue in the UADT by OMI could be possible. Of six indices used to characterize cell metabolism we calculated, the FLIRR showed the most significant differences between tissue types.

Integrated quantum clocks exemplify ultracold-atom-based quantum sensors that rely on lasers as a crucial component. Precise control over the quantum states of ions and atoms used in such devices necessitates lasers with narrow linewidths, high spectral stability, and minimal phase noise. To transfer the absolute spectral characteristics to the cooling and trapping lasers, frequency combs come into play. A reduction of the intrinsic linewidths of frequency combs below a few kHz without need of locking to an optical stabilization cavity would simplify quantum clock experiments significantly. Frequency combs based on mode-locked Er:fiber oscillators are state-of-the-art systems exhibiting several advantages over solid-state lasers like compactness, alignment-free operation and robustness against environmental influences. By employing supercontinuum generation, amplification stages and nonlinear conversion processes, the wavelength range of fiber frequency combs can be extended from 420 to more than 2000 nm. Fiber frequency combs typically have comb lines with an intrinsic optical linewidth in the range of several tens of kilohertz. The broadening of the linewidth is attributed to factors such as pump-induced noise, sensitivity on environmental effects as well as on quantum noise effects. In our recent work we have demonstrated frequency combs exhibiting exceptionally low phase noise resulting in comb linewidths as low as 700 Hz. In this work we employ this technique aiming intrinsically narrow linewidths at wavelengths used in an integrated quantum clock experiment based on Strontium atoms (813 nm, 689 nm).

We present a Er:fiber based frequency comb with intrinsic comb linewidths in the order of 1 kHz at 689 nm and 813 nm. This opens the way of direct laser cooling of Strontium atoms without the need of locking the frequency comb to optical reference cavities. This was achieved by detailed examination of contributions to the oscillator's phase noise. The oscillator was engineered to be insensitive on pump-noise fluctuations resulting in a low phase noise operation mode of the frequency comb system. The frequency comb generated by the improved oscillator has been proven to show linewidths at 1 kHz at 689 nm. The stability of the absolute position of the comb tooth is determined by the stability of the Rubidium RF-source used to lock the frequency comb.

We present time resolved measurements on low dimensional nanomaterials like individual (6,4) single-walled carbon nanotubes and monolayers of MoSe2 via transient interferometric scattering (TiSCAT) microscopy. For this a novel fiber laser system was developed comprising a tunable probe arm and low noise performance. The sensitivity of the measurement is demonstrated for very low excitation powers to prevent photodamage of the sample. Signal variations close to the shot-noise limit can be resolved even with low excitation powers in the order of 1 μW. In combination with the tunability of the laser system the absorption spectrum of a single SWCNT was determined.

We will present our latest innovations about ultrafast fiber lasers and show how multiphoton microscopy can benefit from these developments. Wavelengths around 900 nm and pulse durations as short as 100 fs remain a challenge for fiber lasers. Here we present a two-color femtosecond fiber laser system with synchronous outputs. One arm emits pulses at a central wavelength of 780 nm and the novel second laser arm is continuously tunable in its central wavelength between 810 nm and 950 nm. This allows the independent excitation of NADH and FAD and therefore enables optical metabolism and oxygen imaging of cells via FLIM and PLIM measurements.

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Summary form only given. Several nonlinear microscopy and spectroscopy techniques like SHG, THG, SRS and CARS benefit from pulsed laser systems with tunable central frequency allowing selective excitation of energy levels [1-4]. We present a fiber laser based pulsed two-arm laser system which is compact, robust, cost-effective and fully automated with regard to the adjustment of the central frequency. Both arms are seeded by the same fiber oscillator at a repetition rate of 80 MHz and can be temporally overlapped by an internal 500 ps delay. One arm is based on the TOPTICA FemtoFiber ultra 780 and emits pulses at a central frequency of 780 nm with a pulse duration of around 1 ps (FWHM) and an average power of 500 mW.

Mid- infrared ultrafast pulses are of interest in different applications ranging from vibrational spectroscopy, strong field physics (stable CEP) to detection of trace quantities of compounds. The traditional approach uses solid state lasers, i.e. mature but sensitive technology that is restricted to laboratory use due to its complexity. In real-world applications, ultrashort fiber lasers offer a more rugged, portable and scalable platform for the generation of tunable, brilliant mid-IR femtosecond pulses. This paper will cover approaches for the generation of high-intensity femtosecond pulses in the mid-IR region by means of DFG. The DFG technique also opens up new avenues for frequency comb applications and tunable absolute optical frequency sources. It can be used to set up intrinsically phase stable amplified laser systems as well. The power scalability of lasers with doped Thulium fibers made it possible to generate supercontinua in the mid-IR. Our mid-IR sources along with the availability of high power fiber optics, double clad doped gain fibers and LMA fibers for the 2μm and 1μm region enables "all fiber" compact and robust sources that can be man-portable.

Over past three decades ultrafast lasers have come a long way from the bulky, demanding and very sensitive scientific research projects to widely available commercial products. For the majority of this period the titanium-sapphire-based ultrafast systems were the workhorse for scientific and emerging industrial and biomedical applications. However the complexity and intrinsic bulkiness of solid state lasers have prevented even larger penetration into wider array of practical applications. With emergence of femtosecond fiber lasers, based primarily on Er-doped and Yb-doped fibers that provide compact, inexpensive and dependable fs and ps pulses, new practical applications have become a reality. The overview of current state of the art ultrafast fiber sources, their basic principles and most prominent applications will be presented, including micromachining and biomedical implementations (ophthalmology) on one end of the pulse energy spectrum and 3D lithography and THz applications on the other.

In-vivo microscopic long term time-lapse studies require controlled imaging conditions to preserve sample viability. Therefore it is crucial to meet specific exposure conditions as these may limit the applicability of established techniques. In this work we demonstrate the use of third harmonic generation (THG) microscopy for long term time-lapse three-dimensional studies (4D) in living Caenorhabditis elegans embryos employing a 1550 nm femtosecond fiber laser. We take advantage of the fact that THG only requires the existence of interfaces to generate signal or a change in the refractive index or in the χ3 nonlinear coefficient, therefore no markers are required. In addition, by using this wavelength the emitted THG signal is generated at visible wavelengths (516 nm) enabling the use of standard collection optics and detectors operating near their maximum efficiency. This enables the reduction of the incident light intensity at the sample plane allowing to image the sample for several hours. THG signal is obtained through all embryo development stages, providing different tissue/structure information. By means of control samples, we demonstrate that the expected water absorption at this wavelength does not severely compromise sample viability. Certainly, this technique reduces the complexity of sample preparation (i.e. genetic modification) required by established linear and nonlinear fluorescence based techniques. We demonstrate the non-invasiveness, reduced specimen interference, and strong potential of this particular wavelength to be used to perform long-term 4D recordings.

Live microscopy techniques (i.e., differential interference contrast, confocal microscopy, etc.) have enabled the understanding of the mechanisms involved in cells and tissue formation. In long-term studies, special care must be taken in order to avoid sample damage, restricting the applicability of the different microscopy techniques. We demonstrate the potential of using third-harmonic generation (THG) microscopy for morphogenesis/embryogenesis studies in living Caenorhabditis elegans (C. elegans). Moreover, we show that the THG signal is obtained in all the embryo development stages, showing different tissue/structure information. For this research, we employ a 1550-nm femtosecond fiber laser and demonstrate that the expected water absorption at this wavelength does not severely compromise sample viability. Additionally, this has the important advantage that the THG signal is emitted at visible wavelengths (516 nm). Therefore, standard collection optics and detectors operating near maximum efficiency enable an optimal signal reconstruction. All this, to the best of our knowledge, demonstrates for the first time the noninvasiveness and strong potential of this particular wavelength to be used for high-resolution four-dimensional imaging of embryogenesis using unstained C. elegans in vivo samples.

We report on the frequency doubling of an Erbium-doped master-oscillator power-amplifier system. The fundamental 72 fs pulses at a wavelength of 1.56 μm are frequency doubled to 780 nm and compressed in a Gires-Tournois-interferometer mirror pair to a duration of 55 fs with an average power of 172 mW with an efficiency of 48 %. To our knowledge these are the shortest pulses ever reported from a frequency-doubled fiber-laser system.

C. elegans embryogenesis, at the cell division stage, was imaged using third harmonic generation microscopy employing ultrashort pulsed lasers at 1028nm and 1550nm. This technique could be used for cell tracking studies without fluorescent markers.

On a femtosecond timescale, we observe how Coulomb screening and collective scattering build up in an extreme nonequilibrium electron-hole plasma photoinjected in GaAs. To this end, we generate the plasma via interband excitation with a 10 fs laser pulse. The subsequent polarization response of the system is probed with uncertainty-limited temporal resolution using ultrabroadband terahertz spectroscopy. We show that the intrinsic material becomes conductive instantaneously upon carrier injection, whereas collective effects such as Coulomb screening and plasmon scattering exhibit a delayed onset. Thus, the ultrafast formation of dressed quasiparticles is directly monitored for the first time. The timescale for these phenomena is of the order of the inverse plasma frequency. Our findings support recent quantum kinetic simulations.