The development of Fourier Transform (FT) spectral techniques in the soft X-ray spectral region has been advocated in
the past as a possible route to constructing a bench-top size spectral imager with high spatial and spectral resolution.
The crux of the imager is a soft X-ray interferometer. Auxiliary subsystems include a wide-band soft X-ray source,
focusing optics and detection systems. When tuned over a sufficiently large range of path delays, the interferometer will
sinusoidally modulate the source spectrum centered at the core wavelength of interest, the spectrum illuminates a target,
the reflected signal is imaged onto a CCD, and data acquired for different frames is converted to spectra in software by
using FT methods similar to those used in IR spectrometry producing spectral image per each pixel. The use of shorter
wavelengths results in dramatic increase in imaging resolution, the modulation across the beam width results in highly
efficient use of the beam spectral content, facilitating construction of a bench-top instrument. With the predicted <0.1eV
spectral and <100 nm spatial resolution, the imager would be able to map core-level shift spectra for elements such as
Carbon, which can be used as a chemical compound fingerprint and imaging intracellular structures.
We report on our progress in the development of a Fourier Transform X-ray (FTXR) interferometer. The enabling
technology is X-ray beam splitting mirrors. The mirrors are not available commercially; multi layers of quarter-wave
films (used in IR and visible) are not suitable, and several efforts by other researchers who used parallel slits met only a
very limited success. In contrast, our beam splitters use thin (about 200 nm) SiN membranes perforated with a large
number of very small holes prepared in our micro-fabrication laboratory at JPL. Precise control of surface roughness
and high planarity are needed to achieve the requisite wave coherency. The beam splitters prepared-to-date had surface
RMS and planarity better that <0.3 nm over a 0.45 mm x 1.4 mm area, meeting requirements for spectral imaging at
100eV. Efforts to improve the mirror flatness to a level required for core-level shifts of Carbon are under way.
The development of Fourier Transform (FT) spectral techniques in the soft X-ray (100eV to 500eV spectral region)
has been advocated in the past as a possible route to constructing a bench-top size spectral imager with high spatial
and spectral resolution. The crux of the imager is the soft X-ray interferometer. The auxiliary subsystems include a
soft X-ray source, focusing optics and a CCD-based detection system. When tuned over a sufficiently large range of
path delays (frames), the interferometer will sinusoidally modulate a spectrum of a wide-band X-ray source centered at
the core wavelength of interest with high resolving power. The spectrum illuminates a target, the reflected signal is
imaged onto a CCD, and data acquired for different frames is converted to spectra in software by using FT methods
similar to those used in IR spectrometry, producing spectral image per each pixel. The use of short wavelengths results
in dramatic increase in imaging resolution over that for IR. Important for future NASA missions, and unlike X-ray
Absorption Near Edge Structure (XANES) that uses intense and in monochromatic beams which only a synchrotron
can deliver, FTXR plans to use a miniature, wide bandwidth X-ray source. By modulating the beam spectrum around
the wavelength of interest, the beam energy is used much more efficiently than with gratings (when only a very small,
monochromatized portion of the radiation is used at one time) facilitating construction of a bench-top instrument. With
the predicted <0.1eV spectral and <100 nm spatial resolution, the imager would be able to map a core-level shift
spectrum for each pixel of the image for elements such as C, Si, Ca, N (Kα-lines) which can be used as a chemical
compound fingerprint and for imaging intracellular structures. For heavy elements it could provide "bonding maps"
(L and M-shell lines), enabling to study fossils of microorganisms on space missions and in returned samples to Earth.
We have initiated development of a Fourier Transform X-ray Reflection (FTXR) spectral imager based on the use of a
Mach-Zender type interferometer. The enabling technology for the interferometer is the X-ray beam splitting mirrors.
The mirrors are not available commercially; multi layers of quarter-wave films are not suitable, requiring a different
approach to beam-splitters than in the visible or IR regions. Several efforts by other researchers used parallel slits or
stripes for partial transmission, with only a very limited success. In contrast, our beam splitters are based on thin
(about 200 nm) SiN membranes perforated with a large number of very small holes, prepared using state-of-art microfabrication
techniques that have only recently become available in our laboratory at JPL. Precise control of surface
roughness and high planarity are needed to achieve the wave coherency required for high-contrast fringe forming. The
perforation design is expected to result in much greater surface flatness, facilitating greater wave coherence than for
the other techniques. We report on our progress in the fabrication of beam splitting mirrors to-date, interferometer
design, modeling, assembly, and experimental results.
NASA's planetary exploration strategy is primarily targeted to the detection of extant or extinct signs of life. Thus, the agency is moving towards more in-situ landed missions as evidenced by the recent, successful demonstration of twin Mars Exploration Rovers. Also, future robotic exploration platforms are expected to evolve towards sophisticated analytical laboratories composed of multi-instrument suites. MEMS technology is very attractive for in-situ planetary exploration because of the promise of a diverse and capable set of advanced, low mass and low-power devices and instruments. At JPL, we are exploiting this diversity of MEMS for the development of a new class of miniaturized instruments for planetary exploration. In particular, two examples of this approach are the development of an Electron Luminescence X-ray Spectrometer (ELXS), and a Force-Detected Nuclear Magnetic Resonance (FDNMR) Spectrometer. The ELXS is a compact (< 1 kg) electron-beam based microinstrument that can determine the chemical composition of samples in air via electron-excited x-ray fluorescence and cathodoluminescence. The enabling technology is a 200-nm-thick, MEMS-fabricated silicon nitride membrane that encapsulates the evacuated electron column while yet being thin enough to allow electron transmission into the ambient atmosphere. The MEMS FDNMR spectrometer, at 2-mm diameter, will be the smallest NMR spectrometer in the world. The significant innovation in this technology is the ability to immerse the sample in a homogenous, uniform magnetic field required for high-resolution NMR spectroscopy. The NMR signal is detected using the principle of modulated dipole-dipole interaction between the sample's nuclear magnetic moment and a 60-micron-diameter detector magnet. Finally, the future development path for both of these technologies, culminating ultimately in infusion into space missions, is discussed.
This paper reports on the design, modeling, fabrication, and characterization of a novel silicon bulk micromachined vibratory rate gyroscope and a 3-axes rotation sensing system using this new type of microgyroscopes designed for microspacecraft applications. The new microgyroscope consists of a silicon four leaf clover structure with a post attached to the center. The whole structure is suspended by four thin silicon cantilevers. This device is electrostatically actuated and detects Coriolis induced motions of the leaves capacitively. A prototype of this microgyroscope has a rotation responsivity (scale factor) of 10.4 mV/deg/sec with scale factor nonlinearity of less than 1%, and a minimum detectable noise equivalent rotation rate of 90 deg/hr, at an integration time of 1 second. The bias stability of this microgyroscope is better than 29 deg/hr. The performance of this microgyroscope is limited by the electronic circuit noise and drift. Planned improvements in the fabrication and assembly of the microgyroscope will allow the use of Q-factor amplification to increase the sensitivity of the device by at least two to three orders of magnitude. This new vibratory microgyroscope offers potential advantages of almost unlimited operational life, high performance, extremely compact size, low power operation, and low cost for inertial navigation and altitude control.
Development and performance of large area (0.5 cm2) junction-down monolithic two- dimensional surface-emitting arrays is reported. This involves fabrication of 45 degree(s) and vertical micromirrors with +/- 2 degree(s) tolerances and < 0.2 RMS smoothness, lapping and polishing of 2 in. diameter wafers with < 10 micrometers thickness tolerances, integration of 100 micrometers thick current spreading electrodes which minimize ohmic losses, large area packaging, and mounting to heat exchangers for long pulse operation and minimum chirp. Single monolithic surface emitter diodes exhibit superior performance (slope efficiencies of (eta) d > 50%, threshold currents of Ith equals 220 mA, and output powers in excess of 720 mW). This projects to power densities > 860 W/cm2 and > 50% differential slope efficiencies for arrays of devices. Large area array operation (scaling) was demonstrated. Uniform lasing was achieved from 0.2 cm X 0.5 cm and 0.5 cm X 1.0 cm active area junction-down monolithic arrays (120 and 600 emitters respectively) using 100 microsecond(s) ec long pulses at a 1% duty cycle. Differential slope efficiencies of > 40% were achieved for rows of 12 emitters, and 8% for the large area arrays. The drop in efficiency was due to current leakage, which limited the output power densities to 150 W/cm2. Chirp in these devices was measured to be < 4 nm at twice the threshold current.
Stabilized in-phase mode oscillation is demonstrated from large-aperture 20-element antiguided diode laser arrays. 20-element resonant optical waveguide arrays emit 160 mW total power at 2.8 x I(th) in a diffraction-limited beam and have high spatial coherence across the entire array. CW operation of nonresonant 20-element array structures is demonstrated to high output power levels.