LiteBIRD, the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and fundamental physics. JAXA selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with its expected launch in the late 2020s using JAXA's H3 rocket. LiteBIRD plans to map the cosmic microwave background (CMB) polarization over the full sky with unprecedented precision. Its main scientific objective is to carry out a definitive search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with an insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. To this end, LiteBIRD will perform full-sky surveys for three years at the Sun-Earth Lagrangian point L2 for 15 frequency bands between 34 and 448 GHz with three telescopes, to achieve a total sensitivity of 2.16 μK-arcmin with a typical angular resolution of 0.5° at 100 GHz. We provide an overview of the LiteBIRD project, including scientific objectives, mission requirements, top-level system requirements, operation concept, and expected scientific outcomes.
We have developed a prototype half-wave plate (HWP) based polarization modulator (PMU) for Cosmic Microwave Background polarization measurement experiments. We built a 1/10 scaled PMU that consists of a 50 mm diameter five-layer achromatic HWP with a moth-eye broadband anti-reflection sub-wavelength structure mounted on a superconducting magnetic bearing. The entire system has cooled below 20 K in a cryostat chamber that has two millimeter-wave transparent windows. A coherent source and the diode detector are placed outside of the cryostat and the millimeter-wave goes through the PMU in the cryostat. We have measured the modulated signal by the PMU, analyzed the spectral signatures, and extracted the modulation efficiency over the frequency coverage of 34-161 GHz. We identified the peaks in the optical data, which are synchronous to the rotational frequency. We also identified the peaks that are originated from the resonance frequency of the levitating system. We also recovered the modulation efficiency as a function of the incident electromagnetic frequency and the data agrees to the predicted curves within uncertainties of the input parameters, i.e. the indices of refraction, thickness, and angle alignment. Finally, we discuss the implication of the results when this is applied to the LiteBIRD low-frequency telescope.
Sapphire, alumina, and silicon present the following characteristics that make them suitable as optical elements for millimeter and sub-millimeter applications: low-loss, high thermal conductivity at cryogenic temperatures, and high refractive index ~3. However, the high index also leads to high reflection. We developed a technique to machine sub-wavelength structures (SWS) as a broadband anti-reflection coating on these materials through laser ablation. We describe here the status of our development: transmission measurements of fabricated samples in a diameter of 34.5 mm agree with predictions, and we are now focusing on increasing the fabrication area with high processing rate. This is motivated by the need of ~500 mm diameter optical elements for the next-generation cosmic microwave background polarization experiments. We show our large area machining method on the alumina and sapphire over an area of < 5200 mm2 with the processing rate of < 4:0 mm3=min:, and the transmission measurements are consistent with the predictions.
LiteBIRD has been selected as JAXA’s strategic large mission in the 2020s, to observe the cosmic microwave background (CMB) B-mode polarization over the full sky at large angular scales. The challenges of LiteBIRD are the wide field-of-view (FoV) and broadband capabilities of millimeter-wave polarization measurements, which are derived from the system requirements. The possible paths of stray light increase with a wider FoV and the far sidelobe knowledge of -56 dB is a challenging optical requirement. A crossed-Dragone configuration was chosen for the low frequency telescope (LFT : 34–161 GHz), one of LiteBIRD’s onboard telescopes. It has a wide field-of-view (18° x 9°) with an aperture of 400 mm in diameter, corresponding to an angular resolution of about 30 arcminutes around 100 GHz. The focal ratio f/3.0 and the crossing angle of the optical axes of 90◦ are chosen after an extensive study of the stray light. The primary and secondary reflectors have rectangular shapes with serrations to reduce the diffraction pattern from the edges of the mirrors. The reflectors and structure are made of aluminum to proportionally contract from warm down to the operating temperature at 5 K. A 1/4 scaled model of the LFT has been developed to validate the wide field-of-view design and to demonstrate the reduced far sidelobes. A polarization modulation unit (PMU), realized with a half-wave plate (HWP) is placed in front of the aperture stop, the entrance pupil of this system. A large focal plane with approximately 1000 AlMn TES detectors and frequency multiplexing SQUID amplifiers is cooled to 100 mK. The lens and sinuous antennas have broadband capability. Performance specifications of the LFT and an outline of the proposed verification plan are presented.
LiteBIRD is a JAXA-led Strategic Large-Class mission designed to search for the existence of the primordial gravitational waves produced during the inflationary phase of the Universe, through the measurements of their imprint onto the polarization of the cosmic microwave background (CMB). These measurements, requiring unprecedented sensitivity, will be performed over the full sky, at large angular scales, and over 15 frequency bands from 34 GHz to 448 GHz. The LiteBIRD instruments consist of three telescopes, namely the Low-, Medium-and High-Frequency Telescope (respectively LFT, MFT and HFT). We present in this paper an overview of the design of the Medium-Frequency Telescope (89{224 GHz) and the High-Frequency Telescope (166{448 GHz), the so-called MHFT, under European responsibility, which are two cryogenic refractive telescopes cooled down to 5 K. They include a continuous rotating half-wave plate as the first optical element, two high-density polyethylene (HDPE) lenses and more than three thousand transition-edge sensor (TES) detectors cooled to 100 mK. We provide an overview of the concept design and the remaining specific challenges that we have to face in order to achieve the scientific goals of LiteBIRD.
We present a breadboard model development status of the polarization modulator unit (PMU) for a low-frequency telescope (LFT) of the LiteBIRD space mission. LiteBIRD is a next-generation cosmic microwave background polarization satellite to measure the primordial B-mode with the science goal of σr < 0.001. The baseline design of LiteBIRD consists of reflective low-frequency and refractive medium-and-high-frequency telescopes. Each telescope employs the PMU based on a continuous rotating half-wave plate (HWP) at the aperture. The PMU is a critical instrument for the LiteBIRD to achieve the science goal because it significantly suppresses 1/f noise and mitigates systematic uncertainties. The LiteBIRD LFT PMU consists of a broadband achromatic HWP and a cryogenic rotation mechanism. In this presentation, we discuss requirements, design and systematic studies of the PMU, and we report the development status of the broadband HWP and the space-compatible cryogenic rotation mechanism.
LiteBIRD is a candidate for JAXA’s strategic large mission to observe the cosmic microwave background (CMB) polarization over the full sky at large angular scales. It is planned to be launched in the 2020s with an H3 launch vehicle for three years of observations at a Sun-Earth Lagrangian point (L2). The concept design has been studied by researchers from Japan, U.S., Canada and Europe during the ISAS Phase-A1. Large scale measurements of the CMB B-mode polarization are known as the best probe to detect primordial gravitational waves. The goal of LiteBIRD is to measure the tensor-to-scalar ratio (r) with precision of r < 0:001. A 3-year full sky survey will be carried out with a low frequency (34 - 161 GHz) telescope (LFT) and a high frequency (89 - 448 GHz) telescope (HFT), which achieve a sensitivity of 2.5 μK-arcmin with an angular resolution 30 arcminutes around 100 GHz. The concept design of LiteBIRD system, payload module (PLM), cryo-structure, LFT and verification plan is described in this paper.
We present our design and development of a polarization modulator unit (PMU) for LiteBIRD space mission. LiteBIRD is a next generation cosmic microwave background (CMB) polarization satellite to measure the primordial B-mode. The science goal of LiteBIRD is to measure the tensor-to-scalar ratio with the sensitivity of δr < 10-3. The baseline design of LiteBIRD is to employ the PMU based on a continuous rotating half-wave plate (HWP) at a telescope aperture with a diameter of 400 mm. It is an essential for LiteBIRD to achieve the science goal because it significantly reduces detector noise and systematic uncertainties. The LiteBIRD PMU consists of a multi-layered sapphire as a broadband achromatic HWP and a mechanism to continuously rotate it at 88 rpm. The whole system is maintained at below 10K to minimize the thermal emission from the HWP. In this paper, we discuss the current development status of the broadband achromatic HWP and the cryogenic rotation mechanism.
Laser direct writing of optical devices and circuits is attracted attention because of its ability of three-dimensional fabrication without any mask[1]. Recently, Yb-fiber or solid-state laser has been commonly used for fabrication in addition to traditional Ti:S laser. However, it is reported that waveguide cannot be fabricated in fused silica by using the fundamental light from Yb-based femtosecond laser[2]. Some groups reported on waveguide fabrication by using second-harmonic beam of such lasers[3], but wavelength conversion using nonlinear process has drawbacks such as destabilization of laser power and beam deformation by walk off.
In this study, we investigated fabrication of low-loss waveguide in fused silica by using the fundamental beam (1030nm) from an Yb solid-state femtosecond laser with a pulse duration of 250 fs. The NA of focusing objective lens was 0.42. The fabricated waveguide was made to have a circular cross-section by shaping laser beam with a slit[4]. We fixed repetition rate to 150 kHz, and identified appropriate scan speed and pulse energy for fabrication of low loss waveguide. Waveguide fabricated with appropriate condition had a propagation loss of 0.2 dB/cm, and this is the first report on optical waveguides in a fused silica fabricated by femto-second laser pulses at a wavelength of 1030nm.
When a linearly polarized light wave propagates in a chiral medium, the polarization plane azimuth rotates
clockwise or counter-clockwise depending on the handedness of the material. This effect is called optical activity.
It can be observed in a number of crystals and organic liquids, however the rotatory power of chiral materials
available in nature is useally very small. That is why chiral planar micro- or nano-structures, which possess a
much stronger rotatory power than natural chrial media, have attracted a considerable attention in recent years.
We demonstrate large optical activity of chiral subwavelength gratings having no in-plane mirror symmetry and
fabricated with metal thin films. For zeroth-order transmitted light, the chirality of these gratings manifests itself
in the non-coplanarity of the electric field vectors at the air- and substrate-sides of the metal layer and can be
interpreted in terms of the surface pllasmon enhanced non-local
light-matter interaction. We demonstrate also
that in all-dielectric subwavelength chiral gratings, the optical activity can be enhanced even stronger by using
waveguide resonance. In the terahertz (THz) region, we obtain rotation of the polarization zimuth of a linearly
polarized THz wave by using double-layered metal chiral structure with complimentary patterns.
Planar chirality can lead to interesting polarization effects whose interpretation has invoked possible violation of reciprocity and time reversality. We show that a quasi-two-dimensional array consisting of gold nanoparticles with no symmetry plane and having sub-wavelength periodicity and thickness exhibits giant specific rotation (~104 °/mm) at normal incidence. The rotation is the same for light incident on the front and back sides of the sample. Such reciprocity manifests three-dimensionality of the structure arising from the asymmetry of light-plasmon coupling at the air-metal and substrate-metal interfaces of the structure. The structures thus enable nanoscale polarization control but violate no symmetry principle.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.