SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
We report on the design and test of a whispering gallery sapphire resonator for which the dominant microwave mode family shows frequency-stable, compensated operation for temperatures above 77 kelvin.
We report on the design and test of a whispering gallery sapphire resonator for which the dominant (WGH xxxsubn11) microwave mode family shows frequency-stable, compensated operation for temperatures above 77 Kelvin. The resonator makes possible a new ultra-stable oscillator (USO) capability that promises performance improvements over the best available crystal quartz oscillators in a compact cryogenic package. A mechanical compensation mechanism, enabled by the difference between copper and sapphire expansion coefficients, tunes the resonator to cancel the temperature variation of sapphire's dielectric constant.
Two 2.2 GHz SAW oscillators using aluminum nitride on sapphire (AlN/Al2O3) delay lines were fabricated. The oscillators were electronically temperature compensated and characterized. One of the oscillators was used as the frequency reference for the Ku band source; the second oscillator is available for continued evaluation. A 15 GHz frequency source was designed and fabricated. The 15 GHz source consists of a Ku band FET oscillator which is phase locked to the frequency multiplied (X7) output of the 2.2 GHz SAW reference source. The Ku band source was built using microstrip circuit designs, which are hybrid compatible. Two wafer runs of 2.2 GHz TED devices were fabricated and evaluated. The devices were mounted on microstrip test substrates and evaluated as 15 GHz divide by 7 circuits. The device evaluation indicated that in their present form the TED is not a practical circuit element.
Cooled sapphire resonator provides ultralow phase noise. Apparatus comprises microwave oscillator operating at nominal frequency of about 8.1 GHz, plus frequency-discriminator circuit measuring phase fluctuations of oscillator output. One outstanding feature of frequency discriminator is sapphire resonator serving as phase reference. Sapphire resonator is dielectric ring resonator operating in "whispering-gallery" mode. Functions at room temperature, but for better performance, typically cooled to operating temperature of about 80 K. Similar resonator described in "Sapphire Ring Resonator for Microwave Oscillator" (NPO-18082).
Hybrid fs/ps coherent anti-Stokes Raman scattering (CARS) thermometry often utilizes ps probe pulses derived from pulse shaping or spectrally filtering the primary laser source or by synchronization with a low repetition rate external laser. This results in limited energy, spectral resolution, and/or repetition rate of the ps probe. In this work, a master-oscillator power-amplifier (MOPA) laser was synchronized to the oscillator of a Ti:sapphire regenerative amplifier to achieve high-energy (600 µJ), narrowband (58 ps) probe pulses at kHz repetition rates. Furthermore, temporal filtering allows the pulse characteristics to be adjusted for each application. At 25 Torr, relevant to high-speed flows, the kHz-rate MOPA system generated signal-to-noise ratios 3× higher in nitrogen and had improved precision relative to a 10 ps probe derived from spectral filtering and the power-amplifier. The MOPA system also enabled single-shot ro-vibrational hybrid fs/ps CARS thermometry in 650 K heated air.
The Differential Absorption Lidar (DIAL) technique is a powerful method for determining meteorological parameters, but it requires high quality of the laser source: high energy, very narrow bandwidth, high wavelength stability, and spectral purity. Although many efforts have been made to improve the lasers in view of these aspects, a satisfactory solution has not been demonstrated up to now. We describe a regenerative amplifier, using a Ti:sapphire laser as master oscillator and an alexandrite laser as slave amplifier, which is expected to meet the requirements for water vapor concentration and temperature measurements.
An experiment has been devised which will validate, in space, a miniature, high-performance receiver. The receiver blends three complementary technologies; high temperature superconductivity (HTS), pseudomorphic high electron mobility transistor (PHEMT) monolithic microwave integrated circuits (MMIC), and a miniature pulse tube cryogenic cooler. Specifically, an HTS band pass filter, InP MMIC low noise amplifier, HTS-sapphire resonator stabilized local oscillator (LO), and a miniature pulse tube cooler will be integrated into a complete 20 GHz receiver downconverter. This cooled downconverter will be interfaced with customized signal processing electronics and integrated onto the space shuttle's 'HitchHiker' carrier. A pseudorandom data sequence will be transmitted to the receiver, which is in low Earth orbit (LEO), via the Advanced Communication Technology Satellite (ACTS) on a 20 GHz carrier. The modulation format is QPSK and the data rate is 2.048 Mbps. The bit error rate (BER) will be measured in situ. The receiver is also equipped with a radiometer mode so that experiment success is not totally contingent upon the BER measurement. In this mode, the receiver uses the Earth and deep space as a hot and cold calibration source, respectively. The experiment closely simulates an actual cross-link scenario. Since the receiver performance depends on channel conditions, its true characteristics would be masked in a terrestrial measurement by atmospheric absorption and background radiation. Furthermore, the receiver's performance depends on its physical temperature, which is a sensitive function of platform environment, thermal design, and cryocooler performance. This empirical data is important for building confidence in the technology.
A room temperature sapphire acoustics resonator incorporated into an oscillator represents a possible opportunity to improve on quartz ultrastable oscillator (USO) performance, which has been a staple for NASA missions since the inception of spaceflight. Where quartz technology is very mature and shows a performance improvement of perhaps 1 dB/decade, these sapphire acoustic resonators when integrated with matured quartz electronics could achieve a frequency stability improvement of 10 dB or more. As quartz oscillators are an essential element of nearly all types of frequency standards and reference systems, the success of MSAR would advance the development of frequency standards and systems for both groundbased and flight-based projects. Current quartz oscillator technology is limited by quartz mechanical Q. With a possible improvement of more than x 10 Q with sapphire acoustic modes, the stability limit of current quartz oscillators may be improved tenfold, to 10(exp -14) at 1 second. The electromagnetic modes of sapphire that were previously developed at JPL require cryogenic temperatures to achieve the high Q levels needed to achieve this stability level. However sapphire fs acoustic modes, which have not been used before in a high-stability oscillator, indicate the required Q values (as high as Q = 10(exp 8)) may be achieved at room temperature in the kHz range. Even though sapphire is not piezoelectric, such a high Q should allow electrostatic excitation of the acoustic modes with a combination of DC and AC voltages across a small sapphire disk (approximately equal to l mm thick). The first evaluations under this task will test predictions of an estimated input impedance of 10 kilohms at Q = 10(exp 8), and explore the Q values that can be realized in a smaller resonator, which has not been previously tested for acoustic modes. This initial Q measurement and excitation demonstration can be viewed similar to a transducer converting electrical energy to mechanical energy and back. Such an electrostatic tweeter type excitation of a mechanical resonator will be tested at 5 MHz. Finite element calculation will be applied to resonator design for the desired resonator frequency and optimum configuration. The experiment consists of the sapphire resonator sandwiched between parallel electrodes. A DC+AC voltage can be applied to generate a force to act on a sapphire resonator. With the frequency of the AC voltage tuned to the sapphire resonator frequency, a resonant condition occurs and the sapphire Q can be measured with a high-frequency impedance analyzer. To achieve high Q values, many experimental factors such as vacuum seal, gas damping effects, charge buildup on the sapphire surface, heat dissipation, sapphire anchoring, and the sapphire mounting configuration will need attention. The effects of these parameters will be calculated and folded into the resonator design. It is envisioned that the initial test configuration would allow for movable electrodes to check gap spacing dependency and verify the input impedance prediction. Quartz oscillators are key components in nearly all ground- and space-based communication, tracking, and radio science applications. They play a key role as local oscillators for atomic frequency standards and serve as flywheel oscillators or to improve phase noise in high performance frequency and timing distribution systems. With ultra-stable performance from one to three seconds, an Earth-orbit or moon-based MSAR can enhance available performance options for spacecraft due to elimination of atmospheric path degradation.
Presented are the experimental and computational results of a study on a new kind of dielectric resonator oscillator (DRO). It consists of a cooled, cylindrically symmetric sapphire resonator surrounded by a metallic shield and is capable of higher Q's than any other dielectric resonator. Isolation of fields to the sapphire by the special nature of the electromagnetic mode allows the very low loss of the sapphire itself to be expressed. Calculations show that the plethora of modes in such resonators can be effectively reduced through the use of a ring resonator with appropriate dimensions. Experimental results show Q's ranging from 3 x 10 to the 8th at 77 K to 10 to the 9th at 4.2 K. Performance is estimated for several types of DROs incorporating these resonators. Phase noise reductions in X-band sources are indicated at values substantially lower than those previously available.
As a result of the wide tunability of the titanium sapphire laser NASA has sited it to be used to perform differential absorption lidar (DIAL) measurements of H2O vapor in the upper and lower troposphere. The titanium sapphire laser can provide a spectrally narrow (0.3 to 1.0 pm), high energy (0.5 to 1.0 J) output at 727, 762, and 940 nm which are needed in the DIAL experiments. This laser performance can be obtained by addressing the line-narrowing issues in a master oscillator and the high energy requirement in a fundamental mode oscillator. By injection seeding, the single frequency property of the master oscillator can produce a line narrow high energy power oscillator. A breadboard model of the titanium sapphire laser that will ultimately be used in NASA lidar atmospheric sensing experiment is being designed. The task was to identify and solve any problem that would arise in the actual laser system. One such problem was encountered in the pump laser system. The pump laser that is designed to pump both the master oscillator and power oscillator is a Nd:YLF laser. Nd:YLF exhibits a number of properties which renders this material an attractive option to be used in the laser system. The Nd:YLF crystal is effectively athermal; it produces essentially no thermal lensing and thermally induced birefringence is generally insignificant in comparison to the material birefringence resulting from the uniaxial crystal structure. However, in application repeated fracturing of these laser rods was experience. Because Nd:YLF rods are not commercially available at the sizes needed for this application a modified pump laser system to replace the Nd:YLF laser rod was designed to include the more durable Nd:YAG laser rods. In this design, compensation for the thermal lensing effect that is introduced because of the Nd:YAG laser rods is included.
We report on the design, construction and test of a new all-cryogenic RF Pound circuit used to stabilize a 100 MHz VCXO. Here, all active and passive RF components used to accomplish the phase modulation and detect a PM to AM conversion have been installed into the cryogenic environment.
Techniques necessary to fabricate a high performance S-band microwave single source using state-of-the-art shallow bulk acoustic wave (SBAW) were explored. The bulk wave structures of the AlN/Al 2O3 were investigated for both the R plane and basal plane of sapphire. A 1.072 GHz SBAW delay line and oscillators were developed. A method of selecting and setting oscillator output frequency by selecting substrate orientation angle was also established.
Explore the source record for details and available documents.
A microwave oscillator is provided which can operate at a temperature of many degrees above absolute zero while providing very low phase noise that has heretofore generally required temperatures within a few degrees K. The oscillator includes a ring-shaped resonant element of ruby (sapphire plus chromium) or iron sapphire crystal, lying adjacent to a resonator element of sapphire, so that the regenerator element lies directly in the magnetic field of the resonator element. The resonator element is substantially devoid of contact with electrically conductive material. Microwave energy of a pump frequency (e.g., 31 GHz) is outputted from the regenerator element, while signal energy (e.g., 10 GHz) is outputted from the resonator element.
Analysis of an application of the rudy maser to a superconducting Cavity Stabilized oscillator shows many attractive features. These derive from the mechancial stability inherent in an all-cryogenic design and from the properties of the ruby maser itself. A multiple-cavity design has been developed to allow physical separation of the high-Q superconducting cavity and the ruby element with its requried applied magnetic field. Mode selection is accomplished in this design by tuning the ruby by means of the applied field. We conclude that such an oscillator would perform well, even with cavity Q's as low as 10 to the 8th power allowing the use of a superconductor-on-sapphire resonator with its greater rigidity and lower thermal expansion. A first test of the Superconducting Cavity Stabilized Maser Oscillator (SCSMO) confirms the efficacy of the multiple-cavity design and the applicability of the ruby maser. Frequency variation less than 4x10 to the minus 11th power was measured in the stabilized mode and is attributed to the reference oscillator and to instabilities in the pump source. Variation of 10 to the minus 10th power was observed in the low-Q unstabilized mode, again attributable to pump fluctuations. Even so, direct scaling to a Q of 10 the 9th power predicts a stability better than 10 to the minus 15th power. Together with results showing the lowest losses to date in sapphire at microwave frequencies, and preliminary experiments on superconductor-on-sapphire resonators, frequency stability, levels as low as 10 to the minus 17th power are indicated.
We present an optical model of the MEDLI2 radiometer, which was flown onboard the Mars 2020 vehicle during atmospheric entry on February 18, 2021. The proposed model takes into account the radiometer geometry and optical phenomena such as reflection, refraction, and absorption to estimate the signal loss inherent in the design of the radiometer. The model serves as a filter, which can be used to convert predicted total radiative heat fluxes on the radiometer window into predicted measured heat fluxes, enabling more accurate comparisons of the radiometer flight data with predicted radiometer measurements. Optical properties of the radiometer’s sapphire window are inferred from spectral transmissivity measurements. A modified Lorentz Oscillator Model is used to represent the dielectric function of the window and is fit to the transmission data. The resulting optical model of the radiometer is validated against experimental data used to measure the dependence of the radiometer output voltage on the incident angle of the light impinging on it. Comparison of predicted radiometer measurements with the MEDLI2 flight data show good agreement between the predicted and measured peak heat fluxes, though offset at different times. A linear increase in the signal loss due to radiometer optics alone is also demonstrated, suggesting that the changing shock angle over the course of the trajectory impacts the signal loss.
Mid-infrared spectroscopy, an important technique for sensing molecules, has encountered barriers from sources either limited in tuning range or excessively bulky for widespread use. We present a compact, efficient, and broadly tunable optical parametric oscillator surmounting these challenges. Leveraging dispersion-engineered thin-film lithium niobate-on-sapphire photonics and a singly resonant cavity allows broad, controlled tuning over an octave from 1.5–3.3 µm. The device generates >25mW of mid-infrared light at 3.2 µm with 15% conversion efficiency. The ability to precisely control the device’s mid-infrared emission enables spectroscopy of methane and ammonia, demonstrating our approach’s relevance for sensing. Our work signifies an important advance in nonlinear photonics miniaturization, bringing practical field applications of high-speed, broadband mid-infrared spectroscopy closer to reality.
Until recently, the generation of super-octave continua in bulk materials at full repetition rates of femtosecond (fs) oscillators has been limited to a few special cases of Kerr lens mode-locked Ti:sapphire lasers. In 2019, we described a 3.4-octave fs source with 50 nJ pulse energy at the repetition rate of 78 MHz based on polycrystalline Cr:ZnS [Vasilyev et al. , Optica 6 , 126 ( 2019 ) OPTIC8 2334-2536 10.1364/OPTICA.6.000126 ]. Here we explain the mechanism of fs supercontinuum generation in transition-metal doped polycrystalline II-VI semiconductors at relatively low (nJ-level) pulse energy. We demonstrate that this new supercontinuum regime is enabled by a complex, yet well-reproducible, interplay between the effects arising from the third-order nonlinearity, the quadratic nonlinearities, and thermal optical effects in the medium. We also demonstrate the control of fs pulse propagation in disordered χ <#comment/> ( 2 ) media via the control of the material microstructure.