David L. Dickensheets

Micromachined scanning confocal optical microscope

We have constructed a miniature confocal optical microscope for monochromatic imaging that uses single-mode fiber illumination and a two-phase off-axis zone plate objective lens. The scanning mechanism consists of two micromachined silicon torsional scanning mirrors with orthogonal axes of rotation. The objective lens is made of fused silica and has a N.A. of 0.24 at lambda = 0.6328 microm, with a 1.0-mm working distance. The device is side looking, with die dimensions of 1.2 mm x 2.5 mm x 6.5 mm. We have measured 1.0-microm resolution over a 100-microm field of view.

Silicon-micromachined scanning confocal optical microscope

We describe a miniature scanning confocal optical microscope constructed from components micromachined using silicon and fused silica. The design, fabrication, and characterization of the components of the microscope as well as the assembly of the system are described. Sample images acquired using the instrument are also presented.

A novel miniature confocal microscope/Raman spectrometer system for biomolecular analysis on future Mars missions after Antarctic trials

Biomolecules, such as the productive and protective pigments of photosynthetic organisms, are good biomarkers in extreme Antarctic deserts as analogues of early Mars. Laser Raman technology at long wavelengths which minimize fluorescence is ideal for remote analysis of biomolecules in situ. We report Raman spectra obtained with a prototype miniature laser-Raman spectrometer/confocal microscope (specification < 1 kg) under development for a Mars lander and evaluation in Antarctic deserts. We compare the efficiency of its 852 nm laser/CCD detector system with an optimal bench-top 1064 nm FT Raman spectrometer which excels with biomolecules. Using a yellow Antarctic lichen, Acarospora chlorophana, we show good correlation between both instruments restricted to the 460–1350 cm−1 wavenumber range.

3-D MOEMS mirror for laser beam pointing and focus control

A biaxial torsion scan mirror with a deformable membrane surface is described. The 700-mm-diameter optical surface can be tilted /spl plusmn/4/spl deg/ about two orthogonal axes and can be deformed to a parabola with greater than 3-mm sag at the membrane center. The surface, therefore, acts as a lens with variable focal length ranging from /spl infin/ to 10 mm. Mirror architecture and applications in three-dimensional beam pointing and scanning are discussed.

Micromachined silicon nitride deformable mirrors for focus control

We have built a 1000mum-diameter silicon nitride deformable mirror for focus-control applications, using micro-optoelectromechanical systems technology. We achieved variable focal lengths from 36 to 360 mm while maintaining zero primary spherical aberration, using a maximum control voltage of 100 V. Active control of spherical aberration of approximately two waves at 660 nm was demonstrated.

MEMS-based handheld confocal microscope for in-vivo skin imaging

This paper describes a handheld laser scanning confocal microscope for skin microscopy. Beam scanning is accomplished with an electromagnetic MEMS bi-axial micromirror developed for pico projector applications, providing 800x600 (SVGA) resolution at 56 frames per second. The design uses commercial objective lenses with an optional hemisphere front lens, operating with a range of numerical aperture from NA=0.35 to NA=1.1 and corresponding diagonal field of view ranging from 653 μm to 216 μm. Using NA=1.1 and a laser wavelength of 830 nm we measured the axial response to be 1.14 μm full width at half maximum, with a corresponding 10%-90% lateral edge response of 0.39 μm. Image examples showing both epidermal and dermal features including capillary blood flow are provided. These images represent the highest resolution and frame rate yet achieved for tissue imaging with a MEMS bi-axial scan mirror.

Scanned optical fiber confocal microscope

The size and weight of conventional optical microscopes often makes them inconvenient for use on the human body or for in-situ examination during materials processing. We describe a new fiber-optic scanning confocal optical microscope which could have a total outside diameter as small as 1 mm, and should lend itself to applications in endoscopy or to optical in vivo histology. The first experimental device utilizes a single-mode optical fiber for illumination and detection. The scanning element is a mechanically resonant fused silica cantilever 1.5 cm long and 0.8 mm across, with a micromachined two-phase zone plate objective mounted at one end. The cantilever is electrostatically scanned near resonance in two dimensions, generating a Lissajous pattern which is scan converted to conventional video for real time display or digitization. The objective lens has N.A. equals 0.25 at (lambda) equals 0.6328 micrometers , with a measured spot size of 1.8 micrometers FWHM.

Raman spectroscopic detection of biomolecular markers from Antarctic materials: evaluation for putative Martian habitats.

The vital UV-protective and photosynthetic pigments of cyanobacteria and lichens (microbial symbioses) that dominate primary production in Antarctic desert ecosystems auto-fluoresce at short-wavelengths. A long wavelength (1064 nm) near infra-red laser has been used for non-intrusive Raman spectroscopic analysis of their ecologically significant compounds. There is now much interest in the construction of portable Raman systems for the analysis of cyanobacterial and lichen communities in the field; to this extent, Raman spectra obtained with laboratory-based systems operating at wavelengths of 852 and 1064 nm have been evaluated for potential fieldwork applications of miniaturised units. Selected test specimens of the cyanobacterial Nostoc commune, epilithic lichens Acarospora chlorophana, Xanthoria elegans and Caloplaca saxicola and the endolithic Chroococcidiopsis from Antarctic sites have been examined in the present study. Although some organisms gave useable Raman spectra with short-wavelength lasers, 1064 nm was the only excitation that was consistently excellent for all organisms. We conclude that a 1064 nm Raman spectrometer, miniaturised using an InGaAs detector, is the optimal instrument for in situ studies of pigmented communities at the limits of life on Earth. This has practical potential for the quest for biomolecules residual from any former surface or subsurface life on Mars.

Doppler optical coherence tomography with a micro-electro-mechanical membrane mirror for high-speed dynamic focus tracking

An elliptical microelectromechanical system (MEMS) membrane mirror is electrostatically actuated to dynamically adjust the optical beam focus and track the axial scanning of the coherence gate in a Doppler optical coherence tomography (DOCT) system at 8 kHz. The MEMS mirror is designed to maintain a constant numerical aperture of approximately 0.13 and a spot size of approximately 6.7 microm over an imaging depth of 1mm in water, which improves imaging performance in resolving microspheres in gel samples and Doppler shift estimation precision in a flow phantom. The mirrors small size (1.4 mm x 1 mm) will allow integration with endoscopic MEMS-DOCT for in vivo applications.

Astrobiological instrumentation for Mars - the only way is down

In this paper, in this edition of the Journal commemorating the life and work of David Wynn-Williams, we consider approaches to the astrobiological investigation of Mars. We provide a brief account of the scientific rationale behind the approach presented here. In particular, we outline the capabilities of the Raman spectrometer for the detection of biomarkers. David Wynn-Williams was an active champion of this instrument who was keen to field-qualify a version in Antarctica with a view to flying a Raman instrument onboard a Mars-bound space mission. We examine a scenario for the deployment of such an instrument in conjunction with other instrumentation and argue that subsurface deployment of scientific instruments is essential if we are to succeed in detecting any evidence that may exist for former life on Mars. We outline a mission scenario - Vanguard - which represents a novel but low-risk, low-cost approach to Mars exploration that was conceived and developed jointly by one of the authors (Ellery) and the late David Wynn-Williams.