NASA Technical Reports Server (NTRS) 20110003005: High-Sensitivity, Broad-Range Vacuum Gauge Using Nanotubes for Micromachined Cavities

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by  NASA Technical Reports Server (NTRS)

quency passive isolation platform to filter reduce size, weight, power, and cost. This work was done by Gerard G. Ortiz,
spacecraft vibrations with voice coil actu- This optical transceiver can be used to William H. Farr, and Jeffrey R. Charles of
ators for active tip-tilt correction below retire risks associated with deep-space Caltech for NASA’s Jet Propulsion Laboratory.
the resonant frequency. optical communications on a planetary Further information is contained in a TSP
The canonical deep-space optical pathfinder mission and is complemen- (see page 1). NPO-46073
communications transceiver makes syn- tary to ongoing lunar and access link de-
ergistic use of innovative technologies to velopments.
Two-Photon-Absorption Scheme for Optical Beam Tracking
This approach reduces cost for free-space optical communication receivers.
NASA’s Jet Propulsion Laboratory, Pasadena, California
A new optical beam tracking ap- This work was done by Gerardo G. Ortiz tion is contained in a TSP (see page 1).NPO-
proach for free-space optical communi- and William H. Farr of Caltech for NASA’s 46063
cation links using two-photon absorp- Jet Propulsion Laboratory. Further informa-
tion (TPA) in a high-bandgap detector
material was demonstrated. This track-
ing scheme is part of the canonical ar-
240
chitecture described in the preceding 240
article. TPA is used to track a long-wave- 300 220 235000 220200
length transmit laser while direct ab- 250 200 200 180
sorption on the same sensor simultane- 200 180 150 160
ously tracks a shorter-wavelength 150 160 100 140
buater eaadc o lfanos.re Trsi hlbiece oTancP oAuns r inewsgap vaoe nPlesIniNvgi tptyhh w ooatfso dm1i,oe5ad5s0e- 1054000 30 20 10 20 30 40 11182400000 54000 30 20 10 10 20 30 40 118460200000
nm. As expected, the responsivity shows 0 0 10 0 0
a linear dependence with incident 1.1 mW 548 µW
power level. The responsivity slope is 4.5
× 10–7 A/W2. Also, optical beam spots 240 135
300 220 140
from the 1,550-nm laser beacon were 130
characterized on commercial charge- 250 200 130 125
200 180
coupled device (CCD) and complemen- 150 160 120 120
tary metal-oxide semiconductor 100 140 110 115
(CMOS) imagers with as little as 13.7 50 100
40 120 40 110
µnWew otfr aocpkteirc atle cphonwoelro g(yse oef ffeigrsu raen) . inTnhois- 30 20 10 10 20 30 40 18000 30 20 10 10 20 30 40 105
vative solution to reduce system com- 0 0 0 0
128 µW 13.7 µW
plexity, improve transmit/receive isola-
tion, improve optical efficiency,
improve signal-to-noise ratio (SNR),
Two-Photon Absorptiongenerated signal levels caused by a 1,550 nm laser focused spot on a silicon
and reduce cost for free-space optical
CMOS focal plane array detector at various power levels. Note that the spot is distinguishable even
communications transceivers. with incident power levels in the 10’s of microwatts.
High-Sensitivity, Broad-Range Vacuum Gauge Using Nanotubes
for Micromachined Cavities
NASA’s Jet Propulsion Laboratory, Pasadena, California
A broad-range vacuum gauge has their extremely small diameters in the (m.f.p.) lengths of molecules increase
been created by suspending a single- range of 1 to 3 nanometers. The meas- due to decreasing pressure. Only those
walled carbon nanotube (SWNT) urement parameter will be the change sensing elements that have a long relax-
(metallic or semiconducting) in a Schot- in conductivity of SWNT due to decreas- ation time can produce a measureable
tky diode format or in a bridge conduc- ing rate of molecular collisions as the response when m.f.p. of molecules in-
tor format, between two electrically pressure inside a chamber decreases. creases (or time between two consecu-
charged mesas. SWNTs are highly sensi- The rate of heat removal approaches tive collisions increases). A suspended
tive to molecular collisions because of a saturation limit as the mean free path SWNT offers such a capability because
32 NASA Tech Briefs, January 2011
of its one-dimensional nature and ultra- negative thermal coefficient material) invention. Inquiries concerning rights for its
small diameter. In the initial approach, from atmosphere to <10–6 Torr. A mea- commercial use should be addressed to:
similar architecture was used as that of a sureable current change in the hun- Innovative Technology Assets Management
SWNT-Schottky diode that has been de- dreds of nA range has been recorded in JPL
veloped at JPL, and has its changing the 10–6Torr regime. Mail Stop 202-233
conductivity measured as the test cham- This work was done by Harish Manohara 4800 Oak Grove Drive
ber is pumped down from atmospheric and Anupama B. Kaul of Caltech for NASA’s Pasadena, CA 91109-8099
pressure to high vacuum (10–7 Torr). Jet Propulsion Laboratory. For more informa- E-mail: [email protected]
Continuous response of decreasing con- tion, contact [email protected]. Refer to NPO-45383, volume and number
ductivity has been measured as a func- In accordance with Public Law 96-517, of this NASA Tech Briefs issue, and the
tion of decreasing pressure (SWNT is a the contractor has elected to retain title to this page number.
Wide-Field Optic for Autonomous Acquisition of Laser Link
This system has application in conventional wide-angle imaging such as low-light cockpit imag-
ing, and in long-range motion detection.
NASA’s Jet Propulsion Laboratory, Pasadena, California
An innovation reported in “Two-
Camera Acquisition and Tracking of a
Flying Target,” NASA Tech Briefs, Vol. 32,
No. 8 (August 2008), p. 20, used a com- 92mm
mercial fish-eye lens and an electronic
imaging camera for initially locating
objects with subsequent handover to an
actuated narrow-field camera. But this
operated against a dark-sky back-
ground. An improved solution involves
an optical design based on custom opti-
cal components for the wide-field opti-
cal system that directly addresses the
key limitations in acquiring a laser sig-
nal from a moving source such as an air-
241 mm
craft or a spacecraft.
The first challenge was to increase the Filter
Mounting
light collection entrance aperture diam-
Flange is
eter, which was approximately 1 mm in Near Center
the first prototype. The new design pre- of Gravity
of Lens with Filter
sented here increases this entrance aper-
Camera.
ture diameter to 4.2 mm, which is equiv-
Focal Plane
alent to a more than 16 times larger
collection area. One of the trades made
Removable Rear
in realizing this improvement was to re- Lens Cell Doubles
strict the field-of-view to +80° elevation as Camera Dust
Seal During I&T.
and 360° azimuth. This trade stems from
practical considerations where laser
beam propagation over the excessively FPA
high air mass, which is in the line of
sight (LOS) at low elevation angles, re- (a) (b)
sults in vulnerability to severe atmos-
pheric turbulence and attenuation. An
additional benefit of the new design is
(a) The custom optical design and ray-trace of the Wide-Field Optical Assembly; and (b) a Conceptual Op-
that the large entrance aperture is main-
tomechanical Designfor holding the optical components and providing interface to the focal plane array
tained even at large off-axis angles when (FPA). The collected light is substantially collimated prior to being passed through the spectral filter.
the optic is pointed at zenith.
The second critical limitation for im- beam. For the narrow band spectral filter be implemented. The collimated beam
plementing spectral filtering in the design to function properly, it is necessary to ad- (and the filter) must be relatively large to
was tackled by collimating the light prior equately control the range of incident an- reduce the incident angle down to only a
to focusing it onto the focal plane. This al- gles at which received light intercepts the few degrees. In the presented embodi-
lows the placement of the narrow spectral filter. When this angle is restricted via col- ment, the filter diameter is more than ten
filter in the collimated portion of the limation, narrower spectral filtering can times larger than the entrance aperture.
NASA Tech Briefs, January 2011 33