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We show wavelength-dependent measurements of Verdet constants and reflection/transmission values for various stoichiometric ratios of Cd1 −x Mn x Te. From the data we derive absorption coefficients that help to design optical isolators for GaAs-based diode lasers.

We present distributed Bragg reflector lasers optimized for strontium-based quantum technology applications at 689.449 nm. The devices achieved optical output powers up to 88 mW, four times more than previously reported, and a spectral linewidth of 0.4MHz.

Space-borne optical frequency references based on spectroscopy of atomic vapors may serve as an integral part of compact optical atomic clocks, which can advance global navigation systems or can be utilized for earth observation missions as part of laser systems for cold atom gradiometers. Nanosatellites offer low launch costs, multiple deployment opportunities, and short payload development cycles, enabling rapid maturation of optical frequency references and underlying key technologies in space. Toward an in-orbit demonstration on such a platform, we have developed a CubeSat-compatible prototype of an optical frequency reference based on the D2 transition in rubidium. A frequency instability of 1.7 × 10 − 12 at 1 s averaging time is achieved. The optical module occupies a volume of 35 c m 3 , weighs 73 g, and consumes 780 mW of power.

This paper presents a GaAs-diode laser-based hybrid integration approach for the realization of very complex, though compact and robust laser modules for QIST applications in the field and in space.

Within the European Space Agency (ESA) activity “Gravitational Wave Observatory Metrology Laser” we designed a laser head to fulfill the LISA laser requirements using a non-NPRO seed laser technology: an external cavity diode laser (ECDL) with resonant optical feedback from an external cavity as master oscillator for further linewidth narrowing. Furthermore, our design features a single-stage fiber amplifier with an amplification factor of about 20 dB. This paper covers the requirements on the laser source for LISA, the design and first results of performance characterization of the laser head breadboard.

For studies of the European Space Agency ESA, Fraunhofer ILT develops and builds narrowband, power-stabilized fundamental mode fiber amplifiers especially for future space-based gravitational-wave detectors, e.g. LISA, and for Earth gravity field missions. In this paper, we present the status of our ongoing work, based on a highly stable fiber amplifier designed for a Next Generation Gravity field Mission (NGGM) pre-study, towards power scaling as well as enhancement of the Technology Readiness Level (TRL). Our amplifier has already demonstrated to meet the requirements for future gravity field missions. It features a design that is free of stimulated Brillouin scattering (SBS) and a feedback loop for power stabilization.

We present the requirements, design, and tests of a potential laser system for the Laser Interferometer Space Antenna (LISA) mission as well as a potential frequency stabilization system.

We present the technical realization of a compact system for performing experiments with cold $^{87}{\text{Rb}}$ and $^{39}{\text{K}}$ atoms in microgravity in the future. The whole system fits into a capsule to be used in the drop tower Bremen. One of the advantages of a microgravity environment is long time evolution of atomic clouds which yields higher sensitivities in atom interferometer measurements. We give a full description of the system containing an experimental chamber with ultra-high vacuum conditions, miniaturized laser systems, a high-power thulium-doped fiber laser, the electronics and the power management. In a two-stage magneto-optical trap atoms should be cooled to the low $\mu$K regime. The thulium-doped fiber laser will create an optical dipole trap which will allow further cooling to sub-$\mu$K temperatures. The presented system fulfills the demanding requirements on size and power management for cold atom experiments on a microgravity platform, especially with respect to the use of an optical dipole trap. A first test in microgravity, including the creation of a cold Rb ensemble, shows the functionality of the system.

Semiconductor laser technology has shown to be a promising alternative to other laser technologies, e.g. solid state lasers, for employment in coherent satellite communication and fundamental physics applications. Being compact, robust, energy- and cost-efficient these semiconductor lasers fulfill the key mandatory requirements for deployment in space. At the Ferdinand-Braun-Institut, we have developed a versatile technology platform for integration of any two semiconductor chips, be they active (e.g. laser, amplifier) or passive (e.g. phase modulator), in a fiber coupled laser module wherein all components are either space qualified or space compatible. Here we present a narrow linewidth high power laser module based on this platform that will be used in an iodine-based optical reference onboard a sounding rocket. We discuss its electro-optical performance. We further give an outlook on an ultra-narrow linewidth technology demonstrator laser module.

We present the status of our efforts to develop very compact and robust diode laser modules specifically suited for quantum optics experiments in the field and in space. The paper describes why hybrid micro-integration and GaAs-diode laser technology is best suited to meet the needs of such applications. The electro-optical performance achieved with hybrid micro-integrated, medium linewidth, high power distributed-feedback master-oscillator-power-amplifier modules and with medium power, narrow linewidth extended cavity diode lasers emitting at 767 nm and 780 nm are briefly described and the status of space relevant stress tests and space heritage is summarized. We also describe the performance of an ECDL operating at 1070 nm. Further, a novel and versatile technology platform is introduced that allows for integration of any type of laser system or electro-optical module that can be constructed from two GaAs chips. This facilitates, for the first time, hybrid micro-integration, e.g. of extended cavity diode laser master-oscillator-poweramplifier modules, of dual-stage optical amplifiers, or of lasers with integrated, chip-based phase modulator. As an example we describe the implementation of an ECDL-MOPA designed for experiments on ultra-cold rubidium and potassium atoms on board a sounding rocket and give basic performance parameters.

A flexible method to measure the modulation efficiency and residual amplitude modulation, including non-linearities, of phase modulators is presented. The method is based on demodulation of the modulated optical field in the optical domain by means of a heterodyne interferometer and subsequent analysis of the I&Q quadrature components of the corresponding RF beat note signal. As an example, we determine the phase modulation efficiency and residual amplitude modulation for both the TE and TM modes of a GaAs chip-based phase modulator at the wavelength of 1064 nm. From the results of these measurements, we estimate the linear and quadratic electro-optic coefficients for a P-p-n-N GaAs/AlGaAs double heterostructure.

We present a micro-integrated extended cavity diode laser module for experiments on rubidium Bose–Einstein condensates and atom interferometry at 780.24 nm onboard a sounding rocket. The micro-integration concept is optimized for space application. The laser chip, micro-lenses, a volume holographic Bragg grating, micro-temperature sensors and a micro-thermoelectric cooler are integrated on an aluminium nitride ceramic micro-optical bench with a foot print of only 50 × 10 mm2. Moveable parts are omitted to allow for a very compact and robust design. The laser module provides an output power of more than 120 mW at a short term (170 μs) linewidth of 54 kHz, both full-width-at-half-maximum. The laser can be coarsely tuned by 44 GHz with a continuous tuning range of 31 GHz. The micro-integration technology presented here can be transferred to other wavelengths.

We have developed, assembled, and flight-proven a stable, compact, and autonomous extended cavity diode laser (ECDL) system designed for atomic physics experiments in space. To that end, two micro-integrated ECDLs at 766.7 nm were frequency stabilized during a sounding rocket flight by means of frequency modulation spectroscopy (FMS) of 39^K and offset locking techniques based on the beat note of the two ECDLs. The frequency stabilization as well as additional hard- and software to test hot redundancy mechanisms were implemented as part of a state-machine, which controlled the experiment completely autonomously throughout the entire flight mission., 10 pages, 7 figures

We have realized a laser platform based on GaAs diode lasers that allows for an operation in mobile exper-imental setups in harsh environments, such as on sounding rockets. The platform comes in two versions: a master-oscillator-power-amplifier and an extended cavity diode laser. Our very robust micro-optical bench has a footprint of 80 x 25 mm2. It strictly omits any movable parts. Master-oscillator-power-amplifier systems based on distributed feedback master oscillators for 767 nm and 780 nm narrow linewidth emission have been implemented by now. A continuous wave optical output power of > 1 W with a power conversion efficiency of > 25% could be achieved. The continuous tuning range of these lasers is on the order of 100 GHz, the linewidth at 10 μs is about 1 MHz. For applications demanding a narrower linewidth we have developed an extended cavity diode laser that achieves a linewidth of 100 kHz at 10 μs. These lasers achieve a continuous spectral tuning range of about 50 GHz and an continuous wave optical power up to 30 mW. The modules have been successfully vibration tested up to 29 gRMS along all three axes and passed 1500 g shocks, again along all 3 axes. Both, master-oscillator-power-amplifiers and extended cavity diode lasers, have been employed in sounding rocket experiments.

RGB-light sources with a coherence length of several meters are required for holographic displays. Furthermore, these emitters must feature a high luminance and must be sufficiently small in size, to be employed in today’s consumer market products. Therefore, an all-semiconductor based solution is preferred. We developed red-emitting semiconductor lasers at 635 nm and 647 nm with internal distributed Bragg reflectors and suitable amplifiers at these wavelengths to boost the lasers output power. We investigated tapered amplifiers containing a ridge-waveguide section as well as truncated tapered designs in master-oscillator power-amplifier configuration (MOPA). This allowed the generation of diffraction limited single mode emission by the MO-chip and subsequent amplification of the radiation by the PA-chip by more than 10 dB, without significantly degrading the coherence properties. We successfully demonstrated an optical output power of more than 300 mW at 635 nm and 500 mW at 647 nm. The radiation featured a linewidth below 10 MHz, which corresponds to a coherence length of at least several meters, well suited for a holographic system.

Autonomous laser frequency stabilization is a prerequisite for future space-borne atomic physics experiments. The KALEXUS experiment performed frequency stabilization of two 767 nm extended cavity diode lasers onboard the TEXUS 53 sounding rocket.

We demonstrate the realization of narrow linewidth, high-power ridge waveguide DFB diode lasers emitting near 780 nm. The effects of the coupling coefficient, the laser chip length, and the fabrication process onto the spectral linewidth are discussed. By optimizing both the cavity length and the coupling coefficient, we achieve an intrinsic spectral linewidth as small as 35 kHz at an output power of 270 mW.

We report on the realization of distributed Bragg reflector laser diodes emitting near a wavelength of 1064 nm in a single longitudinal mode with high output power and kHz-level intrinsic spectral linewidth. Linewidth measurements are performed with a heterodyne measurement setup in which both lasers are weakly locked to each other in order to reject slow frequency drifts. The linewidth is analyzed in dependence of the output power. The FWHM linewidth is almost independent from the output power and corresponds to approximately 180 kHz whereas the intrinsic linewidth decreases with a 1/P out dependence. The minimum intrinsic linewidth is 2 kHz at an output power of 180 mW. The measured intrinsic linewidth is in good correspondence with a theoretical estimation.

Clouds of ultra-cold atoms and especially Bose–Einstein condensates (BEC) provide a source for coherent matter-waves in numerous earth bound experiments. Analogous to optical interferometry, matter-wave interferometers can be used for precision measurements allowing for a sensitivity orders of magnitude above their optical counterparts. However, in some respects the presence of gravitational forces in the lab limits experimental possibilities. In this article, we report about a compact and robust experiment generating Bose–Einstein condensates in the drop tower facility in Bremen, Germany. We also present the progress of building the succeeding experiment in which a two species atom interferometer will be implemented to test the weak equivalence principle with quantum matter.

We report on the realization of narrow linewidth high power DFB diode lasers emitting near 1064 nm in stable longitudinal and lateral single mode. The linewidth is analyzed in dependence of the output power for lasers with cavity lengths of 1 and 2 mm by means of a heterodyne beat note technique. The minimum intrinsic linewidth is 22 kHz FWHM (full width at half maximum, at 100 μ s time scale) for an output power of 150 mW and a cavity length of 2 mm. The minimum total linewidth is mainly determined by technical noise and corresponds to 234 kHz FWHM at an output power of 70 mW. The influence of current noise on the linewidth is investigated and compared for different cavity lengths. Re-broadening at high output power is only observed for the contribution of technical noise to the linewidth. The intrinsic linewidth shows the theoretically expected 1/Pout-dependence at all power levels.

Going Down the Tube Two pillars of modern physics are quantum mechanics and general relativity. So far, both have remained apart with no quantum mechanical description of gravity available. Van Zoest et al. (p. 1540 ; see the Perspective by Nussenzveig and Barata ) present work with a macroscopic quantum mechanical system—a Bose-Einstein condensate (BEC) of rubidium atoms in which the cloud of atoms is cooled into a collective quantum state—in microgravity. By dropping the BEC down a 146-meter-long drop chamber and monitoring the expansion of the quantum gas under these microgravity conditions, the authors provide a proof-of-principle demonstration of a technique that can probe the boundary of quantum mechanics and general relativity and perhaps offer the opportunity to reconcile the two experimentally.

We experimentally demonstrate the possibility of preparing ultracold atoms in the environment of weightlessness at the earth-bound short-term microgravity laboratory Drop Tower Bremen, a facility of ZARM – University of Bremen. Our approach is based on a freely falling magneto-optical trap (MOT) drop tower experiment performed within the ATKAT collaboration (“Atom-Catapult”) as a preliminary part of the QUANTUS pilot project (“Quantum Systems in Weightlessness”) pursuing a Bose–Einstein condensate (BEC) in microgravity at the drop tower [1, 2].

We present micro-integrated diode laser modules operating at wavelengths of 767 and 780 nm for cold quantum gas experiments on potassium and rubidium. The master-oscillator-power-amplifier concept provides both narrow linewidth emission and high optical output power. With a linewidth (10 μs) below 1 MHz and an output power of up to 3 W, these modules are specifically suited for quantum optics experiments and feature the robustness required for operation at a drop tower or on-board a sounding rocket. This technology development hence paves the way toward precision quantum optics experiments in space.

We present a simple method to accurately measure the frequency noise power spectrum of lasers. It relies on creating the beat note between two lasers, capturing the corresponding signal in the time domain, and appropriately postprocessing the data to derive the frequency noise power spectrum. In contrast to methods already established, it does not require stabilization of the laser to an optical reference, i.e., a second laser, to an optical cavity or to an atomic transition. It further omits a frequency discriminator and hence avoids bandwidth limitation and nonlinearity effects common to high-resolution frequency discriminators.

We present a micro-integrated, extended cavity diode laser module for space-based experiments on potassium Bose-Einstein condensates and atom interferometry. The module emits at the wavelength of the potassium D2-line at 766.7 nm and provides 27.5 GHz of continuous tunability. It features sub-100 kHz short term (100 μs) emission linewidth. To qualify the extended cavity diode laser module for quantum optics experiments in space, vibration tests (8.1 g(RMS) and 21.4 g(RMS)) and mechanical shock tests (1500 g) were carried out. No degradation of the electro-optical performance was observed.

Atom interferometers covering macroscopic domains of space-time are a spectacular manifestation of the wave nature of matter. Due to their unique coherence properties, Bose-Einstein condensates are ideal sources for an atom interferometer in extended free fall. In this paper we report on the realization of an asymmetric Mach-Zehnder interferometer operated with a Bose-Einstein condensate in microgravity. The resulting interference pattern is similar to the one in the far-field of a double-slit and shows a linear scaling with the time the wave packets expand. We employ delta-kick cooling in order to enhance the signal and extend our atom interferometer. Our experiments demonstrate the high potential of interferometers operated with quantum gases for probing the fundamental concepts of quantum mechanics and general relativity., Comment: 8 pages, 3 figures; 8 pages of supporting material

Precision time references in space are of major importance to satellite-based fundamental science, global satellite navigation, earth observation, and satellite formation flying. Here we report on the operation of a compact, rugged, and automated optical frequency comb setup on a sounding rocket in space under microgravity. The experiment compared two clocks, one based on the optical D2 transition in Rb, and another on hyperfine splitting in Cs. This represents the first frequency comb based optical clock operation in space, which is an important milestone for future satellite-based precision metrology. Based on the approach demonstrated here, future space-based precision metrology can be improved by orders of magnitude when referencing to state-of-the-art optical clock transitions.

In the development process towards an integration of laser systems into compact modules many key points can be simulated. Yet, a reliable and stable testing environment is needed for a deeper understanding of the system. We present the micro optical bench (MiOB) as an advanced platform for the hybrid micro integration of active and passive optical elements. The modular yet robust design enables the precise mounting of those elements with an accuracy of better than 1 μm. By examples of second harmonic generation, master oscillator power amplifier and external cavity diode laser modules a wide range of applications are addressed. Each module is used to highlight different aspects of the MiOB. Examples are the thermal design of the MiOB that allows the precise heating of selected components without influencing others, the robustness that can withstand different mechanical tests, and the overall stiffness that allows the high precision mounting of volume holographic Bragg gratings.

We demonstrate environmental test results of a compact high-power master oscillator (MO) power amplifier (PA) laser module emitting near 1064 nm. The module is micro-integrated on a footprint of 50 × 10mm 2 , features an output power of 1 W, an intrinsic linewidth of 3.6 kHz, and a FWHM linewidth of 100 kHz. Results of lifetime tests and vibrational tests will be presented. Furthermore, we introduce tuning characteristics of a distributed Bragg reflector laser that can be used as a master oscillator. 2 nm of fast tuneability is realized by placing on-chip heaters close to the Bragg grating.

Narrow linewidth high power lasers find application in fields like coherent optical communication, spectroscopy, or laser cooling. Semiconductor lasers emitting near 1064 nm are in particular interesting as replacements for optically pumped solid state lasers used for coherent optical communication in space.

We report on the realization of a semiconductor laser based master oscillator power amplifier (MOPA) system with high output power and narrow linewidth. The system features an output power of more than 1W in stable single mode operation. The FWHM linewidth is 100 kHz and the minimum intrinsic linewidth is as small as 3.6 kHz. The laser concept presented here may find application in coherent optical communication, specifically in space, or within future precision spectroscopy and quantum optics experiments in harsh environments.

We demonstrate a compact high-power master oscillator (MO) power amplifier (PA) laser module emitting near 1064 nm. The module is micro-integrated on a footprint of 50 x 10mm2. The oscillator is a distributed Bragg reflector laser optimized for narrow linewidth operation. The amplifier consists of a ridge waveguide entry and a tapered section. The module features stable single-mode narrow linewidth emission at an output power of 1W and can be tuned mode-hop free by 450GHz.

We report on the realization of narrow linewidth high power distributed bragg reflector (DBR) lasers. For devices with a front facet reflectivity R f = 30% we obtain a minmum intrinsic linewidth of 12 kHz and a total linewidth of 147 kHz at an output power of 130mW (measurement time = 100 µs). For R f = 1% we report an an intrinsic linewidth of less than 100 kHz and a total linewidth of 1202 kHz at an output power of 1W.

We present a simple technique to actively stabilize the optical path length in an optical fiber. A part of the fiber is coated with a thin, electrically conductive layer, which acts as a heater. The optical path length is thus modified by temperature-dependent changes in the refractive index and the mechanical length of the fiber. For the first time, we measure the dynamic response of the optical path length to the periodic changes of temperature and find it to be in agreement with our former theoretical prediction. The fiber's response to the temperature changes is determined by the speed of sound in quartz rather than by slow thermal diffusion. Making use of this fact, we succeeded in actively stabilizing the optical path length with a closed-loop bandwidth of 3.8 kHz.

Future projects for fundamental research with atom interferometry in space demand for compact and robust laser systems. We present highly integrated diode laser based systems for high precision matter wave interferometry experiments in microgravity.

Bose Einstein Condensates (BEC) opened the way for realization of atomic ensembles with Heisenberg limited uncertainty. In microgravity extremely dilute samples of BEC can be obtained and observed after a free evolution on timescales of seconds. Applications range from atom optics to matter wave interferometry. This has led us to realize a BEC of 10000 87Rb atoms in microgravity. The experimental results (to be published) establish the fact, that in a microgravity environment ultra-large condensates (≈1.5 mm) after a free evolution of 1 second can be observed. In particular, microgravity provides mass independent confining potential which is very important for the research on a mixture of quantum gases.We aim to realize a new setup for multispecies experiments, which can be used in catapult mode doubling the time for microgravity to 9 seconds. The experiment is planned to use 87Rb and 40K as degenerate Bose and Fermi gases respectively and can be used to carry out experiments on interferometry, Bose-Fermi mixtures and tests of the weak equivalence principle in quantum domain. Up to date progress and future prospects of this ambitious and technically challenging project will be presented.

We developed a very robust diode laser module platform for the deployment of cold atom based quantum sensors in space. The micro optical benches, not larger than 80 x 25 mm^2, host MOPA and EDCL modules.

We present a micro-integrated master-oscillator-power-amplifier diode laser system with more than 1W output power at 780.2 nm and narrow linewidth emission. The laser is designed for Rubidium Bose-Einstein condensate experiments in space.