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The strong absorption of liquid water in the infrared (IR) molecular fingerprint region constitutes a challenge for applications of vibrational spectroscopy in chemistry, biology, and medicine. While high-power IR laser sources enable the penetration of ever thicker aqueous samples, thereby mitigating the detrimental effects of strong attenuation on detection sensitivity, a basic advantage of heterodyne-measurement-based methods has—to the best of our knowledge—not been harnessed in broadband IR measurements to date. Here, employing field-resolved spectroscopy (FRS), we demonstrate in theory and experiment fundamental advantages of techniques whose signal-to-noise ratio (SNR) scales linearly with the electric field over those whose SNR scales linearly with radiation intensity, including conventional Fourier-transform infrared (FTIR) and direct absorption spectroscopy. Field-scaling brings about two major improvements. First, it squares the measurement dynamic range. Second, we show that the optimum interaction length with samples for SNR-maximized measurements is twice the value usually considered to be optimum for FTIR devices. In order to take full advantage of these properties, the measurement must not be significantly affected by technical noise, such as intensity fluctuations, which are common for high-power sources. Recently, it has been shown that subcycle, nonlinear gating of the molecular fingerprint signal renders FRS robust against intensity noise. Here, we quantitatively demonstrate this advantage of FRS for thick aqueous samples. We report sub-μg/mL detection sensitivities for transmission path lengths up to 80 μm and a limit of detection in the lower μg/mL range for transmission paths as long as 200 μm.

Modern design tools allow solving a wide set of the most challenging multilayer design problems, but they require a deep knowledge of synthesis methods, and good expertise in applying various design tricks to obtain a good solution. During the last two decades computational performance of modern computers allows one to consider more computationally demanding approaches, including those ones based on deep search methods. Deep search approaches require enumeration of all possibilities on each iteration of a method. The number of different possibilities (layer insertion locations for the needle optimization, layer boundaries for the gradual evolution iteration, layer number for the design cleaner, etc.) is growing with the complexity of the coating. Therefore, the computational time of any deep search method considering all possibilities is also growing dramatically. To mitigate this challenge, we propose to use self-adapting algorithms accumulating information on main computational metrics (the numbers of required iterations, the evolution of merit functions versus iteration, the behavior of the merit function gradient norm). Accumulated information can be efficiently used to complete the computations of promising variants and to interrupt iterations of unfavorable variants very early. Proposed self-adapting and self-learning method serves as a superstructure upon well-known multilayer optimization methods, such as needle optimization, gradual evolution, design cleaner, etc. A huge advantage of the new self-learning method is that it does not require any careful fine tuning during computations. New method can run in completely automatic mode and nevertheless provide high quality solutions of challenging design problems.

Multilayer optical components for ultrafast laser applications operating in the mid-infrared (MIR) spectral range from 3 to 15 μm exhibit optical and physical properties essentially different from those ones of the coatings operating in the visible-near-infrared spectral range, namely, they should (i) comprise layers from special MIR thin-film materials; (ii) contain much thicker layers; (iii) deal with adhesion problems due to high stresses; (iv) deal with regions of O-H absorption in the MIR range; (v) exhibit positive group delay dispersion; (vi) be ultra-broadband in order to support short pulses. The mid-infrared thin film materials Ge, ZnS, YbF3, and LaF3 were carefully characterized. ZnS/YbF3 and Ge/YbF3 dichroic filters specified in the visible, near- and mid-infrared spectral ranged were designed, produced, and characterized. The filters operate at Brewster angle 67.5°. Almost one-octave broadband dispersive mirrors operating in the mid-infrared spectral range were developed for the first time. The mirrors consist of Ge and YbF3 layers, which have not been used before for manufacturing of multilayer dispersive optics. The mirrors compensate group delay dispersion of ultrashort laser pulses accumulated by propagation through 4 mm ZnSe windows and additional residual phase modulation of an ultrashort laser pulse. Using the mirrors, the 86 fs pulses were compressed up to 55 fs.

The proper functioning of living systems and physiological phenotypes depends on molecular composition. Yet simultaneous quantitative detection of a wide variety of molecules remains a challenge1–8. Here we show how broadband optical coherence opens up opportunities for fingerprinting complex molecular ensembles in their natural environment. Vibrationally excited molecules emit a coherent electric field following few-cycle infrared laser excitation9–12, and this field is specific to the sample’s molecular composition. Employing electro-optic sampling10,12–15, we directly measure this global molecular fingerprint down to field strengths 107 times weaker than that of the excitation. This enables transillumination of intact living systems with thicknesses of the order of 0.1 millimetres, permitting broadband infrared spectroscopic probing of human cells and plant leaves. In a proof-of-concept analysis of human blood serum, temporal isolation of the infrared electric-field fingerprint from its excitation along with its sampling with attosecond timing precision results in detection sensitivity of submicrograms per millilitre of blood serum and a detectable dynamic range of molecular concentration exceeding 105. This technique promises improved molecular sensitivity and molecular coverage for probing complex, real-world biological and medical settings. A vibrational spectroscopy technique that measures the electric field emitted from organic molecules following infrared illumination allows their molecular fingerprints to be separated from the excitation background, even in complex biological samples.

We demonstrate ultra-rapid electro-optic sampling (EOS) of octave-spanning mid-infrared pulses centered at 9 μm, implemented by mechanically scanning a mirror with a sonotrode resonating at 19 kHz (forward and backward acquisition at 38 kHz). The instrument records the infrared waveform with a spectral intensity dynamic range of 1.6 × 105 for a single scan over a 1.6-ps delay range, acquired within 26 μs. The purely reflective nature of the delay scanning technique is compatible with broad optical bandwidths, short pulse durations (16 fs, centered at 1030 nm) and high average powers (Watt-level). Interferometric tracking of the sonotrode motion in combination with a predictor-corrector algorithm allows for delay-axis determination with down to single-digit attosecond precision. Ultra-rapid mid-infrared EOS will advance applications such as molecular fingerprinting of static samples as well as tracking of biological processes and chemical reactions and is likely to find new fields of application such as infrared-spectroscopic flow cytometry.

The necessity to precisely determine the delay between ultrashort light pulses is ubiquitous in optical metrology. For pulses originating from the same source, optical-interference-based delay tracking using a monochromatic laser affords precisions of a few attoseconds [1] . However, if the pulses originate from separate modelocked oscillators with detuned repetition frequencies – such as widely employed in dual-frequency-comb spectroscopy [2] and electronically controlled optical sampling (ECOPS) [3] – interferometric delay tracking faces two challenges: (i) the optical phase typically fluctuates independently of the repetition frequency, requiring independent control, and (ii) the interference signal is confined to the time window of the overlap, usually < 1ps.

In optical experiments involving variably-delayed ultrashort pulses, the precise calibration of the delay axis is of paramount importance. This is particularly challenging if interferometric delay tracking (with an auxiliary, monochromatic laser [1] ) cannot readily be implemented, such as in the case when the pulses originate from separate modelocked oscillators with detuned repetition frequencies. In the new scheme of electro-optic delay tracking [2] (i) an optical-phase-stable mid-infrared (MIR) waveform is obtained via intrapulse difference frequency generation (IPDFG) driven by an ultrashort near-infrared pulse and (ii) electro-optically sampled (EOS) using a second (independent) near-infrared gate pulse. IPDFG grants (sub-)attosecond lock of the intensity envelope of the driving near-infrared pulse to resulting MIR waveform [3] , while both IPDFG and EOS exhibit (multi-)percent quantum efficiencies [4] being 2 nd -order nonlinear processes. Here, we demonstrate the elongation of a MIR pulse obtained by IPDFG via a narrowband, Fabry-Perot type multilayer optical filter, providing a monochromatic MIR waveform for electro-optic delay tracking which is robust against variations of the initial MIR pulse. The zero crossings of the resulting MIR waveform are reproducible down to a few tens of attoseconds over a time window of 8 ps, which is sufficient for most condensed-phase measurements.

High group delay dispersion (GDD) is often required for ultrafast laser applications. To achieve GDD level higher than -10000 fs2 in a single mirror setting is difficult due to the high sensitivity to unavoidable production inaccuracies. To overcome the problem, total internal reflection (TIR) based dispersive mirrors have been proposed in theory. In this paper, we report our continuous effort to further design, fabricate and measure TIR based dispersive mirrors.

Electro-optic sampling (EOS) has established itself as one of the main techniques for coherent THz spectroscopy. In recent years, EOS has been pushed towards recording infrared or even optical waveforms, opening up new possibilities for spectroscopy in these spectral regions. In this contribution, we demonstrate the potential of electric-field-resolved detection via EOS for broadband, mid-infrared molecular vibrational spectroscopy. We show that field-resolved spectroscopy can achieve detection sensitivities orders of magnitude higher than state-of-the art Fourier-transform infrared spectroscopy. This is achieved by high-quantum-efficiency non-linear temporal “piercing” and, therefore, isolation of the molecular signal from the orders-of-magnitude stronger impulsive excitation. Thereby limitations due to detector dynamic range and source excitation noise can be avoided. This promises a new level of molecular sensitivity and molecular coverage for probing complex biological samples.

We have compared two kinds of dispersive mirrors (DMs) produced by magnetron sputtering and ion beam sputtering. One of them is a broadband DM which is known as double-angle DM, providing a group delay dispersion (GDD) of $$-40 \mathrm{{fs}}^2$$-40fs2 in the range of 550–1050 nm. The other one is a robust highly dispersive mirror, which provides a GDD of about $$-275 \mathrm{{fs}}^2$$-275fs2 at 800 nm and covers the wavelength range from 690 to 890 nm. For the first time, a comparison between magnetron-sputtering-produced and ion-beam-sputtering-produced dispersive mirrors is performed.

Metal–dielectric phase-shifting multilayer optical elements have been developed, providing broadband, virtually dispersion-free polarization manipulation down to the few-cycle level. These optical elements are A g / A l 2 O 3 mirrors that operate in the spectral range from 500 to 100 nm, exhibiting reflectance higher than 95%, and a differential phase shift between the s- and p-polarization of about 90° distributed over four bounces. The mirrors have been designed, produced, and reliably characterized based on spectral photometric and ellipsometric data using a non-parametric approach as well as a multi-oscillator model. The optical elements were implemented into a few-cycle laser system, where they transformed linearly polarized few-cycle light pulses to circular polarization.

Many existing well-known multilayer design methods are based on so-called greedy algorithms. New deep search algorithms developed for needle optimization, gradual evolution, and design cleaner methods are presented. The algorithms possess machine learning features. The advantages of the deep search methods are demonstrated on a set of examples including the OIC Design Contest 2019.

A new method which employs two mirrors produced in one coating run with anti-phase group delay dispersion (GDD) is proposed to suppress GDD oscillations. The anti-phase GDD is realized by the spectral shift between the two mirrors caused by the non-uniformity and post-deposition annealing, for the first time to the best of our knowledge. The group delay (GD) and GDD oscillations are significantly suppressed by the two anti-phase GDD mirrors. Pulse analysis proves that the pulse quality can be improved after applying the new method. The pulses become shorter and have smaller pre- and post-pulses.

An error self-compensation mechanism is investigated for use during the deposition of optical coatings with broadband optical monitoring. The correlation of thickness errors caused by monitoring procedure is mathematically described. It is shown that this correlation of errors may result in the effect of selfcompensation of errors.

Complementary pair of dispersive multilayers operating in the 2-4 µm spectral range were designed and produced for the first time. The mirrors comprise layers of Si and SiO2 thin-film materials. The pair exhibits unparalleled reflectance exceeding 99.7% and provides a group delay dispersion of (-200) fs2. The mirrors can be used in Cr:ZnS/Cr:ZnSe femtosecond lasers and amplifiers.

Femtosecond enhancement cavities have enabled multi-10-MHz-repetition-rate coherent extreme ultraviolet (XUV) sources with photon energies exceeding 100 eV - albeit with rather severe limitations of the net conversion efficiency and of the duration of the XUV emission. Here, we explore the possibility of circumventing both these limitations by harnessing spatiotemporal couplings in the driving field, similar to the "attosecond lighthouse," in theory and experiment. Our results predict dramatically improved output coupling efficiencies and efficient generation of isolated XUV attosecond pulses.

Recently, the mid-infrared (MIR) spectral region has become more and more interesting for bio-medical laser applications since large organic molecules exhibit their fundamental vibrational and rotational modes in this range[1]. In this rapidly developing research area, high-quality optical interference coatings are highly demanded. In many laser systems (see, for instance [2]), it is required to separate initial high-power near-infrared beams originated from a driving laser from lower power MIR components emerged in a nonlinear crystal through a nonlinear process (for example, frequency difference generation). The corresponding multilayer dichroic filters reflecting the radiation in the near-infrared range and transmitting the MIR radiation are required. The coatings exhibit desired reflectance and phase in a near-infrared range and high transmittance in a required MIR region. The acceptable levels of reflectance and transmittance, width of the high-reflectance and high-transmittance ranges, polarization states as well as the angle of incidence are dependent on the laser setup. Along with the specified spectral performance, non-optical properties such as good adhesion, low mechanical stress, thermal stability, are of outmost importance. Low stress is crucial in order not to deform the laser beam wave front of the entire laser system and to avoid thermal lensing. Therefore, the choice of the appropriate evaporation materials and optimization of the high-vacuum deposition processes on the one hand and selection of optimal design solutions on the other hand are key elements in development of advanced multilayer optics for laser systems.

Vibrational spectroscopy techniques constitute powerful analytical tools for complex chemical samples. Among these techniques, field-resolved infrared spectroscopy (FRS) [1] measures the electric field of waveform-stable ultrashort pulses before and after interaction with a sample under scrutiny, thus providing complete, time-resolved macroscopic information on the collective vibrational response of the sample's microscopic constituents.

Infrared (IR) spectroscopy of liquid biopsies shows high potential to become a non-invasive, cost-efficient and fast diagnostic tool for several types of cancers, acute myocardial infarction, Alzheimer's disease as well as possibly other pathologies [1]. However, interpretation of the disease-induced changes in an IR absorption spectrum remains challenging due to high molecular complexity of the samples. Here we perform for the first time Fourier-Transform IR (FTIR) absorption and non-targeted mass spectrometry (MS) based proteomic measurements of the very same set of human blood plasma samples, collected from lung cancer patients and a control group. This combination shows that the IR spectroscopic fingerprint of lung cancer is caused by differential regulation of a number of plasma proteins. Generally, quantitative analysis of cancer-induced changes in blood composition is of paramount importance for cancer diagnostics, and for improving IR spectroscopic fingerprinting approaches in particular.

Molecular vibrational spectroscopies provide chemically-specific information on complex samples. The label-free nature of these techniques renders them highly attractive for studies of biological processes and medical diagnosis [1,2]. Among these methods, the direct, broadband interrogation of molecular vibrations at their fundamental frequencies in the infrared (IR) molecular fingerprint region, profits from large interaction cross-sections, potentially affording a unique combination of detection sensitivity and molecular coverage. However, the strong absorption of (liquid) water in this spectral range has so far severely limited the applicability of IR vibrational spectroscopy (and microscopy) in transmission geometry. In fact, in most table-top setups, the transmission path length has to be limited to < 10 μm, or attenuated total reflection techniques with even smaller penetration depth are applied. Alternatively, the sample can be dried — however this strongly alters it. For larger thicknesses, the current approach is to use high-brightness sources like quantum cascade lasers, although their applicability is limited due to their narrowband emission and modest intensity stability [3].

Intense Mid-IR pulses with controlled waveforms are an important tool to extend the ponderomotive cut-off in strong field experiments. Especially in high-harmonic generation this can be used towards the generation of water-window harmonics [1]. To compensate for the strongly reduced signal at longer wavelengths (∼ λ−6), higher repetition rates are also desirable, pushing the requirements toward high average power systems.

Advanced broadband dispersive multilayer optical components have become key elements in modern laser systems [1]. Along with well-known dispersive mirrors operating effectively in the systems based on Ti:Sa lasers (∼800 nm) and near-infrared Yb:YAG lasers (∼1030 nm), the dispersive optics technology is being used in 2-μm laser systems based on Thulium- and Holmium[2]. Further development of the technology based on 2.4 μm Cr:ZnS-lasers will extend laser output to 3.2 μm [3,4]. Availability of dispersive optics covering the spectral range from 2 to 3.2 μm is demanded for this promising technology. Until now, the best achievements in this direction was a 1/3-octave dispersive mirror operating in the range 2.2–2.7 μm with the group delay dispersion of −200 fs2 and a high-reflector compensating the third-order dispersion of −3000 fs3[5]. In the present work, a large progress in the development of dispersive optics for 2–4 μm region is reported. The novel 2/3-octave dispersive elements achieve reflectance exceeding 99.6% and group delay values of (−200 fs2) in the entire range from 2 to 3.2 μm. The advanced feature is a very small degradation of reflectance in the OH absorption wavelength range between 2.7 μm and 2.9 μm. Exploitation of typical thin-film materials such as Ta 2 O 5 /SiO 2 and Nb 2 O 5 /SiO 2 do not provide the refractive index ratios, which are large not enough to achieve both high reflectance and desired phase properties. Also, the use of thin-film materials typical for the visible-near-infrared ranges does not allow achieving negative group delay dispersion values required for the development of Cr:ZnS oscillator because of very high oscillations in group delay dispersion. In the present work, the thin-film materials Si and SiO 2 providing a high ratio of the refractive index values of 2.3 are used for the first time for the design and production of dispersive elements in the infrared spectral range 2–3.2 μm.

Femtosecond enhancement cavities (fs-EC), i.e., passive free-space resonators, are commonly used for raising the peak and average power of femtosecond laser pulses to the levels necessary for XUV frequency comb generation via high-order harmonic generation [1] and for augmenting the sensitivity of spectroscopic measurements [2]. Building on previous work on the generation of temporal dissipative Kerr-solitons in fiber- and monolithic microresonators (temporal cavity solitons) [3,4], we demonstrate efficient soliton generation in a fs-EC [5].

Two beamsplitters operating across the near-infrared (770-1050 nm) and mid-infrared (4-8 µm) spectral ranges are developed. For the first time, the beamsplitters based on thin-film materials combinations of ZnS/YbF3 and Ge/YbF3 are investigated. The multilayers operate at the Brewster angle of ZnSe substrate. There are no special temperature conditions. The dichroic coatings are designed, produced, and carefully characterized. Potentials of the ZnS/YbF3 and Ge/YbF3 thin-film material combinations are discussed based on analytical estimations, as well as on optical and non-optical characterization results. The ZnS/YbF3 pair provides high reflectance in the near-infrared spectral range. The Ge/YbF3 solutions exhibit very broadband reflection zones. The Ge/YbF3 coatings are thinner and comprise fewer layers than ZnS/YbF3 multilayers. Ge/YbF3 pair has high potential for design and production of NIR-MIR coatings.

Dispersive mirrors operating in a broadband infrared spectral range are reported for the first time. The mirrors are based on Si/SiO2 thin-film materials. The coatings exhibit reflectance exceeding 99.6% in the spectral range from 2 to 3.2 µm and provide a group delay dispersion of -100 fs2 and -200 fs2 in this range. The fabricated mirrors are expected to be key elements of Cr:ZnS/Cr:ZnSe femtosecond lasers and amplifiers. The mirrors open a new avenue in the development of ultrafast dispersive optics operating in the infrared spectral range.

Temporal dissipative solitons in nonlinear optical resonators are self-compressed, self-stabilizing and indefinitely circulating wave packets. Owing to these properties, they have been harnessed for the generation of ultrashort pulses and frequency combs in active and passive laser architectures, including mode-locked lasers1–4, passive fibre resonators5 and microresonators6–11. Here, we demonstrate the formation of temporal dissipative solitons in a free-space enhancement cavity with a Kerr nonlinearity and a spectrally tailored finesse. By locking a 100-MHz-repetition-rate train of 350-fs, 1,035-nm pulses to this cavity-soliton state, we generate a 37-fs sech²-shaped pulse with a peak-power enhancement of 3,200, which exhibits low-frequency intensity-noise suppression. The power scalability unique to free-space cavities, the unprecedented combination of peak-power enhancement and temporal compression, and the cavity-soliton-specific noise filtering attest to the vast potential of this platform of optical solitons for applications including spatiotemporal filtering and compression of ultrashort pulses and cavity-enhanced nonlinear frequency conversion. Temporal dissipative soliton formation in a free-space femtosecond enhancement cavity with a thin Kerr medium is reported. Locking a 350-fs, 1,035-nm pulse train with a repetition rate of 100 MHz to this cavity-soliton state generates a 37-fs sech2-shaped pulse with a peak-power enhancement of 3,200.

We report Si/SiO2 mirrors operating in the spectral range 2-3.2 um. The coatings exhibit reflectance exceeding 99.6% and provide group delay dispersion of (-100 fs2) and (-200 fs2.) The mirrors are key elements of Cr:ZnS/Cr:ZnSe femtosecond lasers and oscillators.

We developed broadband dichroic filters for pump-probe spectroscopy studying ultrafast dynamics of biological molecules. The filters operating at Brewster angle of ZnSe transmit mid-infrared and reflect near-infrared radiation. Thin-film material combinations were ZnS/YbF3 and Ge/YbF3.

One-micrometer wavelength ultrafast laser emission is transformed to a powerful tool for ultrabroadband mid-infrared spectroscopy., Spectroscopy in the wavelength range from 2 to 11 μm (900 to 5000 cm−1) implies a multitude of applications in fundamental physics, chemistry, as well as environmental and life sciences. The related vibrational transitions, which all infrared-active small molecules, the most common functional groups, as well as biomolecules like proteins, lipids, nucleic acids, and carbohydrates exhibit, reveal information about molecular structure and composition. However, light sources and detectors in the mid-infrared have been inferior to those in the visible or near-infrared, in terms of power, bandwidth, and sensitivity, severely limiting the performance of infrared experimental techniques. This article demonstrates the generation of femtosecond radiation with up to 5 W at 4.1 μm and 1.3 W at 8.5 μm, corresponding to an order-of-magnitude average power increase for ultrafast light sources operating at wavelengths longer than 5 μm. The presented concept is based on power-scalable near-infrared lasers emitting at a wavelength near 1 μm, which pump optical parametric amplifiers. In addition, both wavelength tunability and supercontinuum generation are reported, resulting in spectral coverage from 1.6 to 10.2 μm with power densities exceeding state-of-the-art synchrotron sources over the entire range. The flexible frequency conversion scheme is highly attractive for both up-conversion and frequency comb spectroscopy, as well as for a variety of time-domain applications.

Direct measurement of the electric field of light in the near-infrared is experimentally demonstrated, showing that careful optical filtering allows the time-resolved detection of electric field oscillations with half-cycle durations as short as 2.1 fs, even with a 5 fs sampling pulse. Access to the complete electric field evolution of a laser pulse is essential for attosecond science in general1, and for the scrutiny and control of electron phenomena in solid-state physics specifically2,3,4,5,6. Time-resolved field measurements are routine in the terahertz spectral range, using electro-optic sampling (EOS)7,8,9, photoconductive switches10,11 and field-induced second harmonic generation12,13. EOS in particular features outstanding sensitivity and ease of use, making it the basis of time-resolved spectroscopic measurements14 for studying charge carrier dynamics15,16,17,18,19,20 and active optical devices21. In this Letter, we show that careful optical filtering allows the bandwidth of this technique to be extended to wavelengths as short as 1.2 μm (230 THz) with half-cycle durations 2.3 times shorter than the sampling pulse. In a proof-of-principle application, we measure the influence of optical parametric amplification (OPA) on the electric field dynamics of a few-cycle near-infrared (NIR) pulse.

We developed a high repetition rate optical parametric chirped-pulse amplification (OPCPA) laser system based on fiber-laser-seeded Innoslab to generate few-cycle pulses around 2 µm with passively stable carrier-envelope phase (CEP) by difference frequency generation (DFG). Incorporating a piezo mirror before the DFG stage permits rapid CEP control. The OPCPA system is seeded by a stable supercontinuum generated in bulk material with the picosecond Innoslab pulses. Few-cycle pulses with durations of 17 fs and energies of over 100 μJ were produced in a single OPCPA stage. Three different nonlinear crystals: BBO, BiBO, and LNB were tested in the final parametric amplifier, and their average power related limitations are addressed.

The broadband dispersive mirror based on Si/SiO2 thin-film materials and providing group delay dispersion of -200 fs2 in the spectral range from 2 to 3.2 µm have been successfully developed and produced for the first time. The mirrors open a new avenue in the development of ultrafast optics operating in the infrared spectral range and push forward the ultrafast mid-infrared technology.

Optical monitoring strategies are especially important for reliable control of deposition processes because they allow one to monitor optical thicknesses of coating layers, which are the most important production parameters. The chapter discusses broadband and monochromatic monitoring strategies, direct and indirect monitoring approaches, and passive and active monitoring strategies. In the case of monochromatic monitoring, special attention is given to turning point, level monitoring, and monitoring by swing. The most essential effects connected with optical monitoring, such as error self-compensation effect and cumulative effect of thickness errors, are considered.

Intense, multi-color laser fields permit the control of the ionization of atoms and the steering of electron dynamics. Here, we present the efficient collinear creation of the second and third harmonic of a 790 nm femtosecond laser followed by a versatile field synthesizer for the three color fields' composition. Using the device, we investigate the strong-field ionization of neon by fields composed of the fundamental, and the second or third harmonic. The three-color device offers sufficient flexibility for the coherent control of strong-field processes and for time-resolved pump-probe studies.

A special dielectric edge filter extremely sensitive to any change in refractive indices, layer thicknesses and angle of incidence has been investigated using holographic pump-probe measurements at different intensity values. Different physical processes overlapping in time were found to occur, namely the Kerr effect, free- electron generation and their subsequent trapping. A numerical model was used to reproduce the experimental results and decouple these processes.

The Petawatt Field Synthesizer (PFS) under construction at the Max-Planck Institute for Quantum Optics is an optical parametric chirped pulse amplification (OPCPA) system designed to generate few-cycle pulses with petawatt-scale peak power [1, 2]. Such pulses are of high interest for laser-matter interaction experiments, for example for the generation of isolated attosecond pulses with unprecedented efficiency [3]. Here we report on the current performance and upgrade plans of the OPCPA chain of PFS.

Passive optical resonators are important tools for enhancing the sensitivity of spectroscopic measurements [1], and for enhancing the peak and average power of femtosecond laser pulses to the levels necessary for high-order harmonic generation (HHG), e.g. for the generation of XUV frequency combs [2]. The optical bandwidth and thus the pulse duration in such enhancement cavities (ECs) is typically hmited by the spectral phase curvature inherent to the highly reflective multilayer mirrors.

Intense laser fields with controlled waveform are an important tool in strong-field and attosecond physics. Mid-inirared laser systems based on difference frequency generation (DFG) provide passively carrier-envelope phase (CEP) stable femtosecond pulses [1]. As Mid-IR generation is inherently inefficient, systems based on optical parametric amplification (OPA) and DFG are either limited by the peak power [2] or repetition rate [3].

Recent developments in the synthesis, production and characterization of multilayer optical coatings provide precise group-delay dispersion control over broadband spectral ranges. High laser induced damage threshold of dielectric coatings allow exposing them at high intensity laser radiation on the order of 10–1000 GW/cm2. Until now these coatings have been considered in the linear regime only. At the same time, at the intensities close to the laser-induced damage threshold optical coating exhibit nonlinear effects. Namely, intensity dependent addition to the refractive index n 2 I (Kerr effect) cause variation of the reflectance coefficient [1]. The coatings with predictable increase of reflectance at high intensities can be used for the development of innovative elements for ultrafast optics, special edge filters with extremely steep reflectance slope in the vicinity of the central wavelength were designed, produced and carefully investigated. The coatings exhibit predictable increase of reflectance at high intensities.

We report a challenging design, fabrication and post-production characterization problem of a dispersive mirror supporting the spectral range from 2000 nm to 2200 nm and providing a group delay dispersion of -1000 fssup2/sup. The absolute reflectance in the working range is over 99.95%. The reported mirror is a critical element for Tm and Ho based lasers and paves the way for the development of ultrafast 2 µm lasers with sub-100 fs pulse duration.

A dispersive mirror and a coating uniformity challenge were the topics of the design contest held in conjunction with the 2016 Optical Interference Coatings topical meeting of The Optical Society (OSA). A total of 18 designers from China, France, Germany, Japan, and the United States submitted 38 total designs for problems A and B. Michael Trubetskov submitted the winning designs for all four design challenges. The design problems and the submitted solutions are described and evaluated.

A non-polarizing beam splitter and a light color-mixing challenge were the topics of the design contest held in conjunction with the 2019 Optical Interference Coatings topical meeting of the Optical Society of America. A total of 10 designers from China, France, Germany, Japan, and the United States submitted over 70 designs for problems A and B. The design problems and the submitted solutions are described and evaluated.

Thin films of Ge, ZnS, Y b F 3 , and L a F 3 produced using e-beam evaporation on ZnSe and Ge substrates were characterized in the range of 0.4–12 µm. It was found that the Sellmeier model provides the best fit for refractive indices of ZnSe substrate, ZnS, and L a F 3 films; the Cauchy model provides the best fit for Y b F 3 film. Optical constants of Ge substrate and Ge film as well as extinction coefficients of ZnS, Y b F 3 , L a F 3 , and ZnSe substrate are presented in the frame of a non-parametric model. For the extinction coefficient of ZnS, the exponential model is applicable. Stresses in Ge, ZnS, Y b F 3 , and L a F 3 were estimated equal to ( − 50 ) M P a , ( − 400 ) M P a , 140 MPa, and 380 MPa, respectively. The surface roughness does not exceed 5 nm for all films and substrates.

Broadband dispersive mirrors operating in the mid-infrared spectral range of 6.5–11.5 μm are developed for the first time, to the best of our knowledge. The mirrors comprise Ge and YbF3 layers, which have not been used before for manufacturing of multilayer dispersive optics. The design and production processes are described; mechanical stresses of the coatings are estimated based on experimental data; and spectral and phase properties of the produced mirrors are measured. The mirrors compensate group delay dispersion of ultrashort laser pulses accumulated by propagation through 4 mm ZnSe windows and additional residual phase modulation of an ultrashort laser pulse.

Nowadays, dispersive mirrors are able to cover the wavelength range of 4.5 optical octaves and can be used from 220 nm up to 4500 nm. Various design approaches to dispersive mirrors in visible and near IR are briefly discussed. We consider in more detail two dispersive mirrors representing extreme cases. The first one is a mirror working in the range of 290−360 nm and providing group delay dispersion of -75 fs2. The second one is a mirror working in the range of 2500−4500 nm and providing +500 fs2 of group delay dispersion.

We address the challenge of increasing the bandwidth of high-finesse femtosecond enhancement cavities and demonstrate a broad spectrum spanning 1800 cmsup-1/sup(195 nm) at -10 dB around a central wavelength of 1050 nm in an EC with an average finesse exceeding 300. This will benefit a host of spectroscopic applications, including transient absorption spectroscopy, direct frequency comb spectroscopy, and Raman spectroscopy. The pulse circulating in the EC is composed of only 5.4 optical cycles, at a kilowatt-level average power. Together with a suitable gating technique, this paves the way to the efficient generation of multi-megahertz-repetition-rate isolated extreme ultraviolet attosecond pulses via intracavity high-order harmonic generation.