An efficient low-density grating setup for monochromatization of XUV ultrafast light sources

Ultrafast light sources have become an indispensable tool to access and understand transient phenomenon in material science. However, a simple and easy-to-implement method for harmonic selection, with high transmission efficiency and pulse duration conservation, is still a challenge. Here we showcase and compare two approaches for selecting the desired harmonic from a high harmonic generation source while achieving the above goals. The first approach is the combination of extreme ultraviolet spherical mirrors with transmission filters and the second approach uses a normal-incidence spherical grating. Both solutions target time- and angle-resolved photoemission spectroscopy with photon energies in the 10-20 eV range but are relevant for other experimental techniques as well. The two approaches for harmonic selection are characterized in terms of focusing quality, efficiency, and temporal broadening. It is demonstrated that a focusing grating is able to provide much higher transmission as compared to the mirror+filter approach (3.3 times higher for 10.8 eV and 12.9 times higher for 18.1 eV), with only a slight temporal broadening (6.8% increase) and a somewhat larger spot size (∼30% increase). Overall, our study establishes an experimental perspective on the trade-off between a single grating normal incidence monochromator design and the use of filters. As such, it provides a basis for selecting the most appropriate approach in various fields where an easy-to-implement harmonic selection from high harmonic generation is needed

In Situ Exfoliation Method of Large-Area 2D Materials

2D materials provide a rich platform to study novel physical phenomena arising from quantum confinement of charge carriers. Many of these phenomena are discovered by surface sensitive techniques, such as photoemission spectroscopy, that work in ultra-high vacuum (UHV). Success in experimental studies of 2D materials, however, inherently relies on producing adsorbate-free, large-area, high-quality samples. The method that yields 2D materials of highest quality is mechanical exfoliation from bulk-grown samples. However, as this technique is traditionally performed in a dedicated environment, the transfer of samples into vacuum requires surface cleaning that might diminish the quality of the samples. In this article, a simple method for in situ exfoliation directly in UHV is reported, which yields large-area, single-layered films. Multiple metallic and semiconducting transition metal dichalcogenides are exfoliated in situ onto Au, Ag, and Ge. The exfoliated flakes are found to be of sub-millimeter size with excellent crystallinity and purity, as supported by angle-resolved photoemission spectroscopy, atomic force microscopy, and low-energy electron diffraction. The approach is well-suited for air-sensitive 2D materials, enabling the study of a new suite of electronic properties. In addition, the exfoliation of surface alloys and the possibility of controlling the substrate-2D material twist angle is demonstrated.</p

In-situ exfoliation method of large-area 2D materials

The success in studying 2D materials inherently relies on producing samples of large area, and high quality enough for the experimental conditions. Because their 2D nature surface sensitive techniques such as photoemission spectroscopy , tunneling microscopy and electron diffraction, that work in ultra high vacuum (UHV) environment are prime techniques that have been employed with great success in unveiling new properties of 2D materials but it requires samples to be free of adsorbates. The technique that most easily and readily yields 2dmaterials of highest quality is indubitably mechanical exfoliation from bulk grown samples, however as this technique is traditionally done in dedicated environment, the transfer of these samples into UHV setups requires some form of surface cleaning that tempers with the sample quality. In this article, we report on a simple and general method of \textit{in-situ} mechanical exfoliation directly in UHV that yields large-area single-layered films. By employing standard UHV cleaning techniques and by purpusedly exploiting the chemical affinity between the substrate and the sample we could yield large area exfoliation of transition metal dichalcogenides. Multiple transition metal dichalcogenides, both metallic and semiconducting, are exfoliated \textit{in-situ} onto Au and Ag, and Ge. Exfoliated flakes are found to be sub-milimeter size with excellent crystallinity and purity, as evidenced by angle-resolved photoemission spectroscopy, atomic force microscopy and low-energy electron diffraction. In addition, we demonstrate exfoliation of air-sensitive 2D materials and possibility of controlling the substrate-2D material twist angle

Spectroscopic Evidence for a Three-Dimensional Charge Density Wave in Kagome Superconductor CsV3_3Sb5_5

The recently discovered AV3Sb5 (A=K, Rb, Cs) family, possessing V kagome nets, has received considerable attention due to the topological electronic structure and intriguing correlated phenomena, including an exotic charge density wave (CDW) and superconductivity. Detailed electronic structure studies are essential to unravel the characteristics and origin of the CDW as well as its interplay with superconductivity. Here, we present angle-resolved photoemission spectroscopy (ARPES) measurements for CsV3Sb5 at multiple temperatures and photon energies to reveal the nature of the CDW from an electronic structure perspective. We present evidence for a three-dimensional (3D) CDW order. In the process we also pinpoint a surface state attributed to a Cs terminated surface. This state was previously attributed to band folding band due to a CDW along the c direction or a quantum well state from quantum confinement. The CDW expected 2-fold lattice reconstruction along c axis is observed to be a quadrupling of the unit cell, thus for the first time directly demonstrating the 3D nature of the CDW from the electronic structure perspective. Moreover, this 3D CDW configuration originates from two distinct types of distortions in adjacent kagome layers. These present results not only provide key insights into the nature of the unconventional CDW in CsV3Sb5 but also provides an important reference for further studies on the relationship between the CDW and superconductivity.Comment: 19 pages, 4 figure

Angle-resolved photoemission study of unconventional cuprate superconductors

Understanding unconventional superconductivity remains one of the most important unsolved problems in physics. A particularly noteworthy case is the copper-based high-temperature superconductor, which stands out due to its remarkably high transition temperature and relatively simple structure. These exceptional properties not only make the study of cuprates valuable for potential practical applications but also provide a prominent platform for deepened understanding of many-particle physics. In the realm of quantum materials, angle-resolved photoemission spectroscopy (ARPES) has emerged as an indispensable tool for examining the intricate electronic structure in momentum space. This methodology directly probes the single-particle spectral function and can uncover the underlying microscopic interactions. In recent years, technological advancements have enabled the development and implementation of time-resolved ARPES (tr-ARPES). tr-ARPES allows access to non-equilibrium transient states and provides valuable insights into the correlated dynamic properties. This thesis work is divided into two main parts. The first part focuses on the development of a high-resolution, high harmonic generation (HHG)-based tr-ARPES setup. The second part involves ARPES investigations of hole- and electron-doped cuprate superconductors. The aim of developing the tr-ARPES setup was to have a light source with specific characteristics, including a narrow bandwidth, a wide range of photon energies (covering the entire first Brillouin zone), good temporal resolution (near the transform limit), and a high repetition rate (to mitigate the space charge effect). To meet these requirements, the chosen technical approach is the HHG method, driven by an unusually long laser pulse (~460 fs) and short wavelength (343 nm) from a frequency tripled Yb fiber laser. The selection of photon energy is achieved through switchable multilayer bandpass mirrors and thin film filters to prevent temporal broadening. As a result, we achieve an energy resolution of ΔE = 9, 14, 18, 111 meV for photon energies of hν = 10.8, 18.1, 25.3, 32.5 eV. For the pump pulse, a tunable range from 0.65 μm to 9 μm is provided by a two-stage optical-parametric amplifier. Further developments on the instrumental side is the exploration of using a spherical grating to select the HHG harmonics. This is realized by designing a very low-density grating so that the temporal broadening can be minimized. The spherical grating has been numerically calculated, fabricated, and experimentally characterized. This monochromator solution was compared with the mirror+filter configuration and has shown much higher efficiency (3.3 times higher for 10.8 eV and 12.9 times higher for 18.1 eV) with insignificant temporal broadening (6.8% increase for 18.1 eV). This experimental development provides a compact and efficient layout for ultrafast pulse extraction. In the cuprate section, a thorough investigation was conducted on the optimally doped n-type cuprate (NdCeCuO) using static ARPES. The much-refined experimental conditions have enabled us to obtain unprecedented signal-to-noise ratio and detailed observations in this material. The results demonstrate two distinct sectors of states: the reconstructed main band, which exhibited a gap due to the antiferromagnetic (AF) interactions, and a remaining dispersion observed within this AF pseudogap. This in-gap dispersion forms a 'gossamer' Fermi surface that plays a crucial role in the electron pairing. Additionally, a replica band corresponding to the AF folding feature was observed, displaying a consistent energy difference (approximately 60 meV) in both momentum and temperature dependence, possibly suggesting a connection between the AF order and phonon coupling. Furthermore, the hole-doped cuprate (Bi-2212) was studied using the recently developed tr-ARPES system. Leveraging the use of time-of-flight detection, node-antinode information could be gathered from a single measurement. The dynamics of the in-gap states at the antinode exhibited disparities with the near-node region, potentially reflecting phenomena associated with the pseudogap.Att förstå okonventionell supraledning är fortfarande ett av de viktigaste olösta problemen i modern fysik. Ett särskilt anmärkningsvärt fall är de kopparoxidbaserade högtemperatursupraledarna (kuprater), som sticker ut på grund av sina anmärkningsvärt höga övergångstemperaturer och relativt enkla struktur. Dessa exceptionella egenskaper gör inte bara studier av kuprater värdefulla för potentiella praktiska tillämpningar utan ger också en plattform för att studera mångpartikelfysik. Vinkelupplöst fotoemissionsspektroskopi (ARPES) har etablerat sig som ett oumbärligt verktyg för att studera elektronstrukturen hos kvantmaterial. Denna metod kan experimentellt mäta spektralfunktionen för ett kristalint material och därmed i princip fastställa alla enpartikelegenskaper hos materialet och underliggande mikroskopiska interaktioner. Under de senaste åren har tekniska framsteg möjliggjort utveckling och implementering av tidsupplöst ARPES (tr-ARPES). tr-ARPES ger tillgång till transienta icke-jämviktstillstånd och ger därmed värdefulla insikter i korrelerade systems dynamiska egenskaper. De arbeten som redovisas i denna avhandling är uppdelat i två huvuddelar. Den första delen fokuserar på utvecklingen av en högupplöst tr-ARPES ljuskälla baserad på övertonsgenerering (HHG). Den andra delen omfattar ARPES-undersökningar av hål- och elektrondopade kuprater. Syftet med att utveckla tr-ARPES-ljuskällan var att ha åstadkomma en ljuskälla med specifika egenskaper såsom smal bandbredd, ett brett spektrum av fotonenergier (som täcker hela den första Brillouin-zonen), bra tidsupplösning (nära transformgränsen) och en hög repetitionsfrekvens (för att mildra rymdladdningseffekten). För att uppfylla dessa krav valdes HHG, driven av en ovanligt lång laserpuls (~460 fs) med kort våglängd (343 nm) från en frekvenstripplad Yb-fiberlaser. Valet av fotonenergi uppnås genom utbytbara flerskiktsbandpasspeglar och tunnfilmsfilter för att förhindra tidsmässig breddning. Med denna approach uppnår vi en energiupplösning på ΔE = 9, 14, 18, 111 meV för fotonenergier på hν = 10.8, 18.1, 25.3, 32.5 eV. En kontinuerligt valbar pumppuls tillhandahålls i området 0.65 μm till 9 μm av en tvåstegs optisk-parametrisk förstärkare. Fortsatt experimentellt utvecklingsarbete på den instrumentella sidan har gjorts för att utforska användandet av sfäriska gitter som ett alternativ för att välja HHG-övertoner. Detta har realiserats genom att utforma ett gitter med mycket låg linjedensitet så att den tidsmässiga breddningen kan minimeras. Det sfäriska gittret har beräknats numeriskt, tillverkats och experimentellt karakteriserats. En monokromator baserad på denna metod har jämförts med spegel+filter-konfigurationen och har visat mycket högre verkningsgrad (3.3 gånger högre för 10.8 eV och 12.9 gånger högre för 18.1 eV) med obetydlig tidsmässig breddning (6.8% ökning för 18.1 eV). Detta arbete ger därmed en kompakt och effektiv lösning för att extrahera ultrasnabba pulser från en HHG källa. Inom ramen för arbetet på kuprater genomfördes en grundlig undersökning av den optimaldopade n-typ kupraten (NdCeCuO) med statisk ARPES. De mycket förfinade experimentella förhållandena har gjort det möjligt för oss att nå ettoöverträffat signal-brusförhållande. Resultaten har visat på två distinkta tillståndssektorer: den rekonstruerade Fermiytan, som uppvisar ett gap på grund av den antiferromagnetiska (AF) interaktionen, samt en kvarvarande spökfermiyta som kvarstår inom AF-pseudogapet. Denna spökfermiyta spelar en avgörande roll för bildandet av elektronpar. Dessutom visar experimenten ett replikband som uppträder som en kopia av det rekonstruerade bandet och som konsekvent är skiftat till högre bindningsenergi med ca. 60 meV. Denna energiskillnad tycks oberoende av både rörelsemängd och temperatur, vilket möjligen tyder på en koppling mellan AF-ordningen och elektron-phononinteraktionen. Utöver studierna av NdCuCuO har dessutom den håldopade kupraten (Bi-2212) studerats med det nyligen utvecklade tr-ARPES-systemet. Användandet av flygtidsdetektion har möjliggjort parallel mätning av dynamiken från nod till antinod. Dynamiken i tillstånden i gapet vid antinoden uppvisar skillnader med nära-nodregionen, vilket tentativt kan vara relaterat till pseudogapet vid antinoden.QC 2023-05-31</p

Angle-resolved photoemission study of unconventional cuprate superconductors

Understanding unconventional superconductivity remains one of the most important unsolved problems in physics. A particularly noteworthy case is the copper-based high-temperature superconductor, which stands out due to its remarkably high transition temperature and relatively simple structure. These exceptional properties not only make the study of cuprates valuable for potential practical applications but also provide a prominent platform for deepened understanding of many-particle physics. In the realm of quantum materials, angle-resolved photoemission spectroscopy (ARPES) has emerged as an indispensable tool for examining the intricate electronic structure in momentum space. This methodology directly probes the single-particle spectral function and can uncover the underlying microscopic interactions. In recent years, technological advancements have enabled the development and implementation of time-resolved ARPES (tr-ARPES). tr-ARPES allows access to non-equilibrium transient states and provides valuable insights into the correlated dynamic properties. This thesis work is divided into two main parts. The first part focuses on the development of a high-resolution, high harmonic generation (HHG)-based tr-ARPES setup. The second part involves ARPES investigations of hole- and electron-doped cuprate superconductors. The aim of developing the tr-ARPES setup was to have a light source with specific characteristics, including a narrow bandwidth, a wide range of photon energies (covering the entire first Brillouin zone), good temporal resolution (near the transform limit), and a high repetition rate (to mitigate the space charge effect). To meet these requirements, the chosen technical approach is the HHG method, driven by an unusually long laser pulse (~460 fs) and short wavelength (343 nm) from a frequency tripled Yb fiber laser. The selection of photon energy is achieved through switchable multilayer bandpass mirrors and thin film filters to prevent temporal broadening. As a result, we achieve an energy resolution of ΔE = 9, 14, 18, 111 meV for photon energies of hν = 10.8, 18.1, 25.3, 32.5 eV. For the pump pulse, a tunable range from 0.65 μm to 9 μm is provided by a two-stage optical-parametric amplifier. Further developments on the instrumental side is the exploration of using a spherical grating to select the HHG harmonics. This is realized by designing a very low-density grating so that the temporal broadening can be minimized. The spherical grating has been numerically calculated, fabricated, and experimentally characterized. This monochromator solution was compared with the mirror+filter configuration and has shown much higher efficiency (3.3 times higher for 10.8 eV and 12.9 times higher for 18.1 eV) with insignificant temporal broadening (6.8% increase for 18.1 eV). This experimental development provides a compact and efficient layout for ultrafast pulse extraction. In the cuprate section, a thorough investigation was conducted on the optimally doped n-type cuprate (NdCeCuO) using static ARPES. The much-refined experimental conditions have enabled us to obtain unprecedented signal-to-noise ratio and detailed observations in this material. The results demonstrate two distinct sectors of states: the reconstructed main band, which exhibited a gap due to the antiferromagnetic (AF) interactions, and a remaining dispersion observed within this AF pseudogap. This in-gap dispersion forms a 'gossamer' Fermi surface that plays a crucial role in the electron pairing. Additionally, a replica band corresponding to the AF folding feature was observed, displaying a consistent energy difference (approximately 60 meV) in both momentum and temperature dependence, possibly suggesting a connection between the AF order and phonon coupling. Furthermore, the hole-doped cuprate (Bi-2212) was studied using the recently developed tr-ARPES system. Leveraging the use of time-of-flight detection, node-antinode information could be gathered from a single measurement. The dynamics of the in-gap states at the antinode exhibited disparities with the near-node region, potentially reflecting phenomena associated with the pseudogap.Att förstå okonventionell supraledning är fortfarande ett av de viktigaste olösta problemen i modern fysik. Ett särskilt anmärkningsvärt fall är de kopparoxidbaserade högtemperatursupraledarna (kuprater), som sticker ut på grund av sina anmärkningsvärt höga övergångstemperaturer och relativt enkla struktur. Dessa exceptionella egenskaper gör inte bara studier av kuprater värdefulla för potentiella praktiska tillämpningar utan ger också en plattform för att studera mångpartikelfysik. Vinkelupplöst fotoemissionsspektroskopi (ARPES) har etablerat sig som ett oumbärligt verktyg för att studera elektronstrukturen hos kvantmaterial. Denna metod kan experimentellt mäta spektralfunktionen för ett kristalint material och därmed i princip fastställa alla enpartikelegenskaper hos materialet och underliggande mikroskopiska interaktioner. Under de senaste åren har tekniska framsteg möjliggjort utveckling och implementering av tidsupplöst ARPES (tr-ARPES). tr-ARPES ger tillgång till transienta icke-jämviktstillstånd och ger därmed värdefulla insikter i korrelerade systems dynamiska egenskaper. De arbeten som redovisas i denna avhandling är uppdelat i två huvuddelar. Den första delen fokuserar på utvecklingen av en högupplöst tr-ARPES ljuskälla baserad på övertonsgenerering (HHG). Den andra delen omfattar ARPES-undersökningar av hål- och elektrondopade kuprater. Syftet med att utveckla tr-ARPES-ljuskällan var att ha åstadkomma en ljuskälla med specifika egenskaper såsom smal bandbredd, ett brett spektrum av fotonenergier (som täcker hela den första Brillouin-zonen), bra tidsupplösning (nära transformgränsen) och en hög repetitionsfrekvens (för att mildra rymdladdningseffekten). För att uppfylla dessa krav valdes HHG, driven av en ovanligt lång laserpuls (~460 fs) med kort våglängd (343 nm) från en frekvenstripplad Yb-fiberlaser. Valet av fotonenergi uppnås genom utbytbara flerskiktsbandpasspeglar och tunnfilmsfilter för att förhindra tidsmässig breddning. Med denna approach uppnår vi en energiupplösning på ΔE = 9, 14, 18, 111 meV för fotonenergier på hν = 10.8, 18.1, 25.3, 32.5 eV. En kontinuerligt valbar pumppuls tillhandahålls i området 0.65 μm till 9 μm av en tvåstegs optisk-parametrisk förstärkare. Fortsatt experimentellt utvecklingsarbete på den instrumentella sidan har gjorts för att utforska användandet av sfäriska gitter som ett alternativ för att välja HHG-övertoner. Detta har realiserats genom att utforma ett gitter med mycket låg linjedensitet så att den tidsmässiga breddningen kan minimeras. Det sfäriska gittret har beräknats numeriskt, tillverkats och experimentellt karakteriserats. En monokromator baserad på denna metod har jämförts med spegel+filter-konfigurationen och har visat mycket högre verkningsgrad (3.3 gånger högre för 10.8 eV och 12.9 gånger högre för 18.1 eV) med obetydlig tidsmässig breddning (6.8% ökning för 18.1 eV). Detta arbete ger därmed en kompakt och effektiv lösning för att extrahera ultrasnabba pulser från en HHG källa. Inom ramen för arbetet på kuprater genomfördes en grundlig undersökning av den optimaldopade n-typ kupraten (NdCeCuO) med statisk ARPES. De mycket förfinade experimentella förhållandena har gjort det möjligt för oss att nå ettoöverträffat signal-brusförhållande. Resultaten har visat på två distinkta tillståndssektorer: den rekonstruerade Fermiytan, som uppvisar ett gap på grund av den antiferromagnetiska (AF) interaktionen, samt en kvarvarande spökfermiyta som kvarstår inom AF-pseudogapet. Denna spökfermiyta spelar en avgörande roll för bildandet av elektronpar. Dessutom visar experimenten ett replikband som uppträder som en kopia av det rekonstruerade bandet och som konsekvent är skiftat till högre bindningsenergi med ca. 60 meV. Denna energiskillnad tycks oberoende av både rörelsemängd och temperatur, vilket möjligen tyder på en koppling mellan AF-ordningen och elektron-phononinteraktionen. Utöver studierna av NdCuCuO har dessutom den håldopade kupraten (Bi-2212) studerats med det nyligen utvecklade tr-ARPES-systemet. Användandet av flygtidsdetektion har möjliggjort parallel mätning av dynamiken från nod till antinod. Dynamiken i tillstånden i gapet vid antinoden uppvisar skillnader med nära-nodregionen, vilket tentativt kan vara relaterat till pseudogapet vid antinoden.QC 2023-05-31</p

"Fat" Nanobeam-Waveguide Resonator for Suppressing Spectral Diffusion in InGaAs Quantum Dots

The coherent coupling of photons to solid state emitters is one of the building blocks for future quantum technology. However, one of the main sources for non-perfect or even strongly reduced coherence of the photons is charge noise which introduces energy shifts during or in between the photon emission events. In particular solid-state emitters in nanostructures suffer from such spectral diffusion as surface charge defects from nanofabrication are often only tens of nanometers away from the emitter. In this thesis, a novel type of light–matter interface, a GaAs-based nanobeam cavity, has been designed and tested to couple emission from self-assembled InAs quantum dot (QD). A wide nanobeam cavity with a modulated outline has been designed and optimized, which possess a high intrinsic quality factor for the fundamental optical mode (10^5 for 450 nm wide cavity and 6*10^4 for 600 nm wide cavity), and is expected to reduce spectral diffusion of the QD originated from the etched defects. First, a Finite Element (Comsol) simulation was used for the design, and secondly, the fabricated design was tested at room and cryogenic temperatures. When the QD was coupled to the wide nanobeam cavity inside cryostat, a fast decay rate of 19 ± 2 ns^(-1) is measured, resulting in a lifetime of ~ 52.6 ps. Comparing with the lifetime of QDs in bulk material, the spontaneous emission lifetime, i.e. Purcell factor, is derived to be ~ 36 under a non-resonant excitation scheme. A lifetime of 52.6 ps corresponds to a lifetime-limited linedwidth of 8.37 GHz. Compared to typical non-Purcell enhanced linewidths of about 200 MHz, a line-width of 8.37 GHz strongly relaxes the sensitivity to charge noise introduced by the environment. Furthermore, and not tested here, the additional distance to surface charges, possible due to the novel "fat" cavity design, should furthermore reduce the induced spectral diffusion as observed before in non-resonant nanostructures

In Situ Exfoliation Method of Large-Area 2D Materials

2D materials provide a rich platform to study novel physical phenomena arising from quantum confinement of charge carriers. Many of these phenomena are discovered by surface sensitive techniques, such as photoemission spectroscopy, that work in ultra-high vacuum (UHV). Success in experimental studies of 2D materials, however, inherently relies on producing adsorbate-free, large-area, high-quality samples. The method that yields 2D materials of highest quality is mechanical exfoliation from bulk-grown samples. However, as this technique is traditionally performed in a dedicated environment, the transfer of samples into vacuum requires surface cleaning that might diminish the quality of the samples. In this article, a simple method for in situ exfoliation directly in UHV is reported, which yields large-area, single-layered films. Multiple metallic and semiconducting transition metal dichalcogenides are exfoliated in situ onto Au, Ag, and Ge. The exfoliated flakes are found to be of sub-millimeter size with excellent crystallinity and purity, as supported by angle-resolved photoemission spectroscopy, atomic force microscopy, and low-energy electron diffraction. The approach is well-suited for air-sensitive 2D materials, enabling the study of a new suite of electronic properties. In addition, the exfoliation of surface alloys and the possibility of controlling the substrate-2D material twist angle is demonstrated.</p

Efficient low-density grating setup for monochromatization of XUV ultrafast light sources

Ultrafast light sources have become an indispensable tool to access and understand transient phenomenon in material science. However, a simple and easy-to-implement method for harmonic selection, with high transmission efficiency and pulse duration conservation, is still a challenge. Here we showcase and compare two approaches for selecting the desired harmonic from a high harmonic generation source while achieving the above goals. The first approach is the combination of extreme ultraviolet spherical mirrors with transmission filters and the second approach uses a normal-incidence spherical grating. Both solutions target time- and angle-resolved photoemission spectroscopy with photon energies in the 10-20 eV range but are relevant for other experimental techniques as well. The two approaches for harmonic selection are characterized in terms of focusing quality, photon flux, and temporal broadening. It is demonstrated that a focusing grating is able to provide much higher transmission as compared to the mirror+filter approach (3.3 times higher for 10.8 eV and 12.9 times higher for 18.1 eV), with only a slight temporal broadening (6.8% increase) and a somewhat larger spot size (∼30% increase). Overall, our study establishes an experimental perspective on the trade-off between a single grating normal incidence monochromator design and the use of filters. As such, it provides a basis for selecting the most appropriate approach in various fields where an easy-to-implement harmonic selection from high harmonic generation is needed