M2 Beam Research Articles

Evidence of Tribological Adaptation Controlled by Tribosynthesis of FeWO4 on an WC-Reinforced Electron Beam M2 Steel Coating Rubbed against a HSS Disk in a Range of Sliding Speeds.

In the present work, the tribological experiments on sliding the electron beam composite M2+WC coating have been carried out with characterization of the sample microstructures and phases both before and after the testing using metallography, SEM, EDS, and XRD. The sliding in the speed range 0.8-3.6 m/s resulted in simultaneous reduction in both wear rate and coefficient of friction with the sliding speed. Investigations showed that such a tribological adaptation was due to the tribochemical generation of lubricative FeWO4 and Fe2WO6 mixed oxides and the generation of a mechanically mixed composite layer on the worn surfaces that consisted of carbide fragments, an oxidized metal matrix, and was lubricated by in-situ formed mixed iron-tungsten oxides.

Design of beam optics for RF-separated kaon and antiproton beams in the M2 beam line of the CERN North Area

The present contribution reviews the principle of RF separation and explains its dependence on different parameters of beam optics and hardware. The first examination of potential showstoppers for the RF-separated beam implementation for Phase-2 of the AMBER experiment in the M2 beam line of the North Area is presented. Different beam optics settings have been examined, providing either focused or parallel beams inside the RF cavities. The separation and transmission capability of the different optics settings for realistic characteristics of RF cavities are discussed and the preliminary results of the potential purity and intensity of the RF-separated beam are presented. These show that a trade-off between the overall beam intensity and the share of the required particle type in the overall beam needs to be established. No showstoppers have been identified for achieving the beam parameters required for AMBER’s kaonic Primakoff reactions, kaon spectroscopy, prompt-photon production and kaon charge-radius programs. However, the high beam intensity requirements of the AMBER Drell–Yan programme cannot be satisfied with an RF-separated beam.

A new double-line waveguide architecture for photonic applications using fs laser writing in Nd3+ doped GeO2-PbO glasses

A new double-line waveguide architecture produced in Nd3+ doped GeO2-PbO glasses is presented for photonic applications. The waveguides are written directly into Nd3+ doped GeO2-PbO glasses using a Ti:Sapphire femtosecond (fs) laser, operating at 800 nm, delivering 30 fs pulses at 10 kHz repetition rate and writing speed of 0.5 mm/s. Two parallel lines form a dual-waveguide each line being a result of either 4 or 8 superimposed lines. Results of propagation losses, M2 beam quality factor at 632 and 1064 nm, refractive index change, and relative gain at the signal wavelength (1064 nm) are presented. Structural changes, due to laser writing process were investigated by Raman spectroscopy. The observed near-field pattern image showed good waveguiding quality, consisting of a single, circular lobe. X,y-symmetrical guiding for both waveguides was observed. The relative gain reached 4.5 and 6.0 dB/cm for 4 and 8 superimposed lines, respectively, for 420 mW of 808 nm pumping. Propagation losses were 0.89 and 0.44 dB/cm, for 4 and 8 superimposed lines, respectively, leading to positive internal gain of 3.6 and 5.56 dB/cm. The results obtained in the present work demonstrate that this new double line architecture for Nd3+ doped GeO2-PbO glasses is promising for the fabrication of integrated amplifiers, lossless components and lasers.

Status of the MUonE experiment

The MUonE experiment has been proposed to measure the differential cross section of μe elastic scattering, by colliding the 160 GeV muons of the CERN M2 beam with atomic electrons of thin target plates. From a very precise measurement of the shape one can achieve a competitive determination of the leading hadronic contribution to the muon magnetic moment, independent from the other existing ones. In preparation for the Test Run with a reduced setup the detector geometry has been optimised. Expected yields for a first physics run with limited statistics are discussed, together with prospects for the assessment of the main systematic uncertainties.

The polarization-aided tunable high-power femtosecond Raman solitons generation from 1.96 to 3.1 μm in fibers cascaded system

We present the demonstration of a polarization-aided high-power ultra-broadband tunable mid-infrared (MIR) Raman soliton-based femtosecond laser in fibers cascaded nonlinear system. We found and verified that the incident pulse polarization has effects on the characteristics of the Raman solitons generation in different types of fluoride fibers. For the first time to the best of our knowledge, we achieved the MIR Raman solitons with central wavelength continuously tunable from 1.96 to 3.1 µm by optimizing the input pulse parameters. The solitons with a maximum average power of above 350 mW, accounting for nearly 83% of the total output power, and the pulse width of these tunable Raman solitons remains below 200 fs. Thanks to the nearly all-fiber configuration, which results in the pump laser with root mean square (RMS) value of power fluctuation around 0.24% in 2 h, and the 3.1-µm soliton with far-field beam M2 value around 1.1. Additionally, the corresponding numerical simulations on these solitons radiation were also conducted, the results are in good agreement with the experimental one.

Strange-Meson Spectroscopy – from COMPASS to AMBER

COMPASS is a multi-purpose fixed-target experiment at CERN’s M2 beam line aimed at studying the structure and spectrum of hadrons. It has collected the so far world’s largest data set on diffractive production of the K−π−π+ final state, which in principle gives access to all strange mesons. Based on this data set, we performed an elaborate partial-wave analysis. It reveals signals in the mass region of well-known states, such as the K*2(1430). In addition, we found indications for a resonance-like signal in the mass region of the K(1630). This state would be a supernumerary state and hence could be a candidate for an exotic strange meson. The partial-wave analysis is limited in some areas by the limited kinematic coverage of the final-state particle identification of the COMPASS setup. To overcome this limitation, we propose a new high-precision strange-meson spectroscopy measurement at the AMBER experiment, which will be located at CERN’s M2 beam line.

M2 beam quality factor from the Delano y-ybar diagram

New graphical methods using the Delano y-ybar diagram are shown to yield simple alternative derivations of the M2 beam quality factor for Gaussian-like laser beams. Using M2 as a scaler for the Lagrange optical invariant, powerful methods of interpreting and calculating the beam factor become apparent. Elegant methods of determining M2 using strategic beam sample locations are also developed, taking advantage of the property that a freely propagating beam trace in the Gaussian beam y-ybar plane is a straight line. Application to non-Gaussian beams is explored.

4F3/2→4I9/2 and 4F3/2→4I13/2 laser operations with a Nd:GdTaO4 crystal

This study investigated the laser performance of a Nd:GdTaO4 crystal for the 4F3/2→4I9/2 and 4F3/2→4I13/2 transitions at 928 nm and 1328 nm, respectively. A 5-mm-thick, 1.4 at.% Nd:GdTaO4 crystal was used in the experiments, under a pump at 879 nm, directly into the 4F3/2 emitting level. At a 10 Hz pump repetition rate, the maximum pulse energy at 928 nm reached 35.7 mJ, with an optical-to-optical efficiency of ~19.3%. When the pump repetition rate increased to 100 Hz, the laser pulse energy decreased to 13.5 mJ; the laser beam was characterised by M2 factors of Mx2 = 1.4 and My2 = 1.8 for the Ox and Oy axis, respectively. The Nd:GdTaO4 crystal yielded laser pulses at 1328 nm with a maximum energy of 9.7 mJ for operation at 10 Hz repetition rate; the overall optical-to-optical efficiency amounted to ~5.2%. Increasing the pump repetition rate to 100 Hz reduced the laser pulse energy to 5.8 mJ; the laser beam M2 factors were Mx2 = 1.2 and My2 = 1.4.

Improvement of beam quality by pump homogenization of Innoslab laser amplifier

The effect of pump homogenization on the beam quality of the output laser is studied for a compact partially end-pumped hybrid-cavity slab laser amplifier, i.e. Innoslab laser amplifier. Using ZEMAX simulation software, two pump coupling modes, direct imaging and homogenization with waveguide were designed, and their effects on the uniformity of light intensity distribution in the slow axis (crystal width) direction of laser diode arrays were compared. It is found that the pump uniformity is significantly improved after the waveguide is homogenized and the influence of the laser diode array luminescence dead pixels on the pump imaging is weakened. Furthermore, the effect of pumping homogenization on the performance of Innoslab laser amplifier is verified by experiments: the uniformity of slow-axis pumping increases from 90.6% to 95.4% after homogenization with waveguide, and the quality of output laser beam M2 increases from 2.41 to 1.55 after three-pass amplification, and the self-oscillation in the cavity is effectively suppressed.

Research on measurement of laser beam M2 factor based on LabVIEW

A new method for measuring the laser beam M2 factor is presented in this paper. Fixed magnification attenuation and focusing optical system is used to irradiate the laser beam to the CCD camera for spot acquisition, the collected spot is detected and processed based on the LabVIEW software platform, then the Zernike polynomial is used to fit and reconstruct the wavefront of the laser spot, the spatial distribution of the laser beam is given in real time, the optical parameters such as M2 factor are obtained. A test device is also set up for verification. The working wavelength is 400∼1100nm, and the measurement accuracy of the M2 factor is ±6 %, it can meet most of the current requirements.

The “Physics Beyond Colliders” Projects for the CERN M2 Beam

Physics Beyond Colliders is an exploratory study aimed at exploiting the full scientific potential of CERN’s accelerator complex up to 2040 and its scientific infrastructure through projects complementary to the existing and possible future colliders. Within the Conventional Beam Working Group (CBWG), several projects for the M2 beam line in the CERN North Area were proposed, such as a successor for the COMPASS experiment, a muon programme for NA64 dark sector physics, and the MuonE proposal aiming at investigating the hadronic contribution to the vacuum polarisation. We present integration and beam optics studies for 100 – 160 GeV/c muon beams as well as an outlook for improvements on hadron beams, which include RFseparated options and low-energy antiproton beams and radiation studies for high intensity beams. In addition, necessary beam instrumentation upgrades for beam particle identification and momentum measurements are discussed.

High power diode laser source with a transmission grating for two spectral beam combining

A novel laser-coupling structure is introduced, in which the same transmission grating is simultaneously employed by two spectral beams generated in identical resonant cavities. The novel structure doubles the number of coupled laser emitters and the output power. Eight 800-nm diode laser bars were coupled and combined with polarization multiplexing, achieving a continuous wavelength power of 212 W, a broad spectrum of 19.1 nm, an M2 (times diffraction limited factor) beam quality of 2.2×16.7 and a brightness of 236MW/cm2/sr.

32.1 W/m2 continuous wave solar-pumped laser with a bonding Nd:YAG/YAG rod and a Fresnel lens

We report here significant progress in solar-pumped laser collection efficiency with a grooved bonding Nd:YAG/YAG crystal rod. A Fresnel lens was used as the primary solar radiation concentrator. A gold-plated conical pump cavity with a water filled quartz tube lens was used to concentrate the solar radiation from the focal zone of the primary concentrator into a 6-mm-diameter, 95-mm-length bonding Nd:YAG/YAG crystal rod. To the best of our knowledge, it is the first time of a bonding Nd:YAG/YAG crystal pumped by Fresnel lens solar energy collection and concentration system. For 1.03 m2 effective solar radiation collection area, 32.1 W/m2 collection efficiency was obtained, corresponding to a total slope efficiency of 5.4% and an optical-to-optical efficiency of 3.3%. The performance of the grooved bonding crystal rod was compared with the grooved non-bonding crystal rod. The maximum output power from the grooved bonding crystal rod was 22.6% higher than the value from a grooved non-bonding rod. The M2 beam quality factor was also improved from 126 to 61.

Femtosecond Yb:YGAG ceramic slab regenerative amplifier

We present a femtosecond regenerative Yb:YGAG (Y3Ga2Al3O12) ceramic slab amplifier delivering 405 fs pulses at a wavelength of 1030 nm with a bandwidth limit of 306 fs, 1.1 W of average power, 8 μJ of pulse energy, and a repetition rate of 100 kHz. The amplifier is seeded by 9 pJ pulses generated by a Yb-doped fiber ring oscillator with extra-cavity spectral shaping to minimize gain narrowing. The net-gain of the pulses is 60 dB, the spectral bandwidth is 4.1 nm (FWHM), and the M2 beam quality factor is < 1.2. Due to similar optical and thermo-mechanical properties to Yb:YAG, the Yb:YGAG gain medium is a promising alternative for upgrading the existing Yb:YAG picosecond disk amplifiers to the femtosecond regime.

Focusing metasurface quantum-cascade laser with a near diffraction-limited beam.

A terahertz vertical-external-cavity surface-emitting-laser (VECSEL) is demonstrated using an active focusing reflectarray metasurface based on quantum-cascade gain material. The focusing effect enables a hemispherical cavity with flat optics, which exhibits higher geometric stability than a plano-plano cavity and a directive and circular near-diffraction limited Gaussian beam with M2 beam parameter as low as 1.3 and brightness of 1.86 × 106 Wsr-1m-2. This work initiates the potential of leveraging inhomogeneous metasurface and reflectarray designs to achieve high-power and high-brightness terahertz quantum-cascade VECSELs.

Amplification of a Q-Switched Ho:GdVO4 Oscillator in Thulium-Doped Large-Mode-Area Fiber

We report a high peak power, narrow linewidth, stable pulsed Ho:GdVO4 amplifier based on thuliumdoped fiber, which produces 6.65 W average output power at 2,048 nm and 56.8 kW peak power with 11.7 ns pulse width at 10 kHz repetition rate. We use a simple Q-switched Ho:GdVO4 laser as a seed laser and a thulium-doped fiber pumped by a 792 nm laser diode as an amplifier. The fiber amplifier provided 6.5 dB gain to the input signal. The spectral linewidth of the Ho:GdVO4 amplifier remains < 0.5 nm with an M2 beam quality of 1.36.

High energy muon induced radioactive nuclides in nickel plate and its use for 2-D muon-beam image profile

Target materials were exposed to a muon beam with an energy of 160GeV/c at the COMPASS experiment line in CERN-SPS to measure the production cross-sections for muon-induced radionuclides. A muon imager containing four nickel plates, each measuring 100mm×100mm, exposed to the IP plate successfully detected the muon beam image during an irradiation period of 33 days. The contrasting density rate of the nickel plate was (5.2±0.7)×10–9 PSL/muon per one-day exposure to IP. The image measured 122mm and 174mm in horizontal and vertical lengths, respectively, in relation to the surface of the base, indicating that 50±6% of the muon beam flux is confined to an area of 18% of the whole muon beam. The number of muons estimated from the PSL value in the total beam image area (0.81±0.1)×1013 was comparable to the total muon counts of the ion-chamber at the M2 beam line in the CERN-SPS. The production cross-sections of Cr-51, Mn-54, Co-56, Co-57, and Co-58 in nickel were 0.19±0.08, 0.34±0.06, 0.5±0.05, 3.44±0.07, 0.4±0.03 in the unit of mb, respectively, reducing muon associated particles effects. They are approximately 10 times smaller than that a proceeding study by Heisinger et al.

Transverse spin and transverse momentum structure of the nucleon from the COMPASS experiment

COMPASS is a fixed target experiment at the CERN SPS M2 beam line, taking data since year 2002. Part of the physics programme is dedicated to the study of the transverse spin and transverse momentum structure of the nucleon, by means of semi-inclusive deeply inelastic lepton scattering (SIDIS). For these measurements, data have been collected using transversely polarised proton (NH 3 ) and deuteron ( 6 LiD) targets. A selection of the results on the azimuthal asymmetries measured is presented, with particular focus on the most recent measurements from the data collected in 2007 and 2010 with the proton target. These results exhibit clear signals for the Collins asymmetry, interpreted as a convolution of a non-zero transversity PDF and Collins fragmentation function, and for the Sivers asymmetry which is related to the Sivers function, the most famous and discussed of the TMD PDFs. The data collected with the 6 LiD target, have also been recently analysed to search for the azimuthal modulations in the production of hadrons which are expected to be present in the unpolarised part of the SIDIS cross-section. The azimuthal hadron asymmetries, which are related to the Boer-Mulders TMD PDF, show strong and somewhat puzzling kinematical dependencies.

Planar Waveguide Laser Optimization and Characterization Employing Real-Time Beam Quality Measurement

We present a methodology for optimizing the output radiance and characterizing a planar waveguide laser utilizing a technique offering “real-time” beam quality measurement. This approach is applicable to lasers in general employing the simultaneous measurement and comparison of a re-imaged cavity-mode beam-waist (near-field) and the power distribution in the far-field (specifically in the Fourier plane of a lens). This approach provides the laser's beam parameter product, and hence M2 beam propagation factor. By exploiting this technique we optimized the performance of a quasi-four-level Nd:YAG planar waveguide laser with an extended stable-cavity configuration, whilst characterizing the in-plane thermal lens. This laser produced a record radiance level of >; 9 TWm-2/sr-1 for this 946-nm transition, with an effective thermal lens focal length >; 400 mm at all incident pump powers up to the maximum level of 87 W.

Yb:YAG single crystal fiber power amplifier for femtosecond sources

We demonstrate a versatile femtosecond power amplifier using a Yb:YAG single crystal fiber operating from 10 kHz to 10 MHz. For a total pump power of 75 W, up to 30 W is generated from the double-pass power amplifier. At a repetition rate of 10 kHz, an output energy of 1 mJ is obtained after recompression. In this configuration, the pulse duration is 380 fs, corresponding to a peak power of 2.2 GW. The M2 beam quality factor is better than 1.1 for investigated parameters.