Demonstration of a compact double-reflection transmissive beam scanner operating at 1550 nm wavelength.

A compact forward-directed transmissive beam scanner operating at a wavelength of 1550 nm was constructed and characterized. The scanner consists of two wire-grid polarizers (WGPs) surrounding a 45° Faraday rotator, causing incident light to reflect once from each WGP before transmitting through the second polarizer. Scanning is achieved by tilting one of the WGPs. Measured efficiency remained above 73% over a 90° forward scan range (-45∘ to +45∘) for vertically polarized incident light. Additionally, we measured the efficiency versus beam deflection for four different incident linear polarization configurations, three of which maintained >70% efficiency for deflection angles up to -60∘.

Sequential RGB color imaging with a millimeter-scale monochrome camera with a rolling shutter.

Applications are growing for ultracompact millimeter-scale cameras. For color images, these sensors commonly utilize a Bayer mask, which can negatively and perceptibly have an impact on image resolution and quality, especially for low pixel-count submillimeter sensors. To alleviate this, we built a time-multiplexed RGB LED illumination system synchronized to the rolling shutter of a monochrome camera. The sequential images are processed and displayed as near real-time color video. Experimental comparison with an identical sensor with a Bayer color mask showed significant improvement in the MTF curves and to perceived image clarity. Trade-offs with respect to system complexity and color motion artifacts are discussed.

MEMS 3D Scan Mirror with SU-8 Membrane and Flexures for High NA Microscopy.

We demonstrate a MEMS beam scanner capable of biaxial scanning with simultaneous focus control, for integration into a handheld confocal microscope for skin imaging. The device is based on a dual axis gimbal structure with an integrated largestroke deformable mirror. SU-8 polymer is used to construct both the deformable membrane as well as the torsional hinges for biaxial scanning. The 4 mm diameter mirror can perform raster pattern scanning with a range of +/- 1.5 degrees and Lissajous scanning with a range of +/- 3 degrees (mechanical scan angle), and has a maximum deflection of 9 um for focus control. The design, fabrication and characterization of the opto-mechanical performance of the MEMS device are presented in this paper.

Wide-field imaging combined with confocal microscopy using a miniature f/5 camera integrated within a high NA objective lens.

Wide-field (WF) imaging paired with reflectance confocal microscopy can noninvasively detect skin cancer with high accuracy. However, two separate devices are required to perform each imaging procedure. We describe a new concept that integrates the two into one device: a miniature WF color camera within the objective lens used for confocal microscopy, providing simultaneous sub-surface cellular imaging and WF surface morphologic imaging. The camera, inserted between a hyperhemisphere front lens and a back lens group of the objective, commands a field of view of 4.0 mm, with a resolution better than 30 µm, while confocal optical sectioning is preserved at sharper than 2.5 µm.

Four-zone varifocus mirrors with adaptive control of primary and higher-order spherical aberration.

Electrostatically actuated deformable mirrors with four concentric annular electrodes can exert independent control over defocus as well as primary, secondary, and tertiary spherical aberration. In this paper we use both numerical modeling and physical measurements to characterize recently developed deformable mirrors with respect to the amount of spherical aberration each can impart, and the dependence of that aberration control on the amount of defocus the mirror is providing. We find that a four-zone, 4 mm diameter mirror can generate surface shapes with arbitrary primary, secondary, and tertiary spherical aberration over ranges of ±0.4, ±0.2, and ±0.15 µm, respectively, referred to a non-normalized Zernike polynomial basis. We demonstrate the utility of this mirror for aberration-compensated focusing of a high NA optical system.

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 800 x 600 (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 microm to 216 microm. Using NA=1.1 and a laser wavelength of 830 nm we measured the axial response to be 1.14 mum full width at half maximum, with a corresponding 10%-90% lateral edge response of 0.39 mum. 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.

MEMS-in-the-lens 3D beam scanner for in vivo microscopy.

The "MEMS-in-the-lens" active lens for a laser scanning microscope comprises a high numerical aperture front element, a 3D+ MOEMS beam scanner and a collimating back lens. The scanner utilizes a silicon gimbal with SU-8 polymer flexures and deformable membrane mirror. The mirror aperture is 4 mm in diameter, and is capable of 9 µm deflection for focus control, with four annular electrodes to allow tuning of primary and secondary spherical aberration. The gimbal supports tip/tilt actuation up to ±3° for lateral beam scanning. We show confocal imaging using a benchtop mockup of the active lens, illustrating the potential for this approach to support 3D microscopy for optical biopsy applications.

MEMS-in-the-lens architecture for a miniature high-NA laser scanning microscope.

Laser scanning microscopes can be miniaturized for in vivo imaging by substituting optical microelectromechanical system (MEMS) devices in place of larger components. The emergence of multifunctional active optical devices can support further miniaturization beyond direct component replacement because those active devices enable diffraction-limited performance using simpler optical system designs. In this paper, we propose a catadioptric microscope objective lens that features an integrated MEMS device for performing biaxial scanning, axial focus adjustment, and control of spherical aberration. The MEMS-in-the-lens architecture incorporates a reflective MEMS scanner between a low-numerical-aperture back lens group and an aplanatic hyperhemisphere front refractive element to support high-numerical-aperture imaging. We implemented this new optical system using a recently developed hybrid polymer/silicon MEMS three-dimensional scan mirror that features an annular aperture that allows it to be coaxially aligned within the objective lens without the need for a beam splitter. The optical performance of the active catadioptric system is simulated and imaging of hard targets and human cheek cells is demonstrated with a confocal microscope that is based on the new objective lens design.

Dermoscopy-guided reflectance confocal microscopy of skin using high-NA objective lens with integrated wide-field color camera.

Reflectance Confocal Microscopy, or RCM, is being increasingly used to guide diagnosis of skin lesions. The combination of widefield dermoscopy (WFD) with RCM is highly sensitive (~90%) and specific (~ 90%) for noninvasively detecting melanocytic and non-melanocytic skin lesions. The combined WFD and RCM approach is being implemented on patients to triage lesions into benign (with no biopsy) versus suspicious (followed by biopsy and pathology). Currently, however, WFD and RCM imaging are performed with separate instruments, while using an adhesive ring attached to the skin to sequentially image the same region and co-register the images. The latest small handheld RCM instruments offer no provision yet for a co-registered wide-field image. This paper describes an innovative solution that integrates an ultra-miniature dermoscopy camera into the RCM objective lens, providing simultaneous wide-field color images of the skin surface and RCM images of the subsurface cellular structure. The objective lens (0.9 NA) includes a hyperhemisphere lens and an ultra-miniature CMOS color camera, commanding a 4 mm wide dermoscopy view of the skin surface. The camera obscures the central portion of the aperture of the objective lens, but the resulting annular aperture provides excellent RCM optical sectioning and resolution. Preliminary testing on healthy volunteers showed the feasibility of combined WFD and RCM imaging to concurrently show the skin surface in wide-field and the underlying microscopic cellular-level detail. The paper describes this unique integrated dermoscopic WFD/RCM lens, and shows representative images. The potential for dermoscopy-guided RCM for skin cancer diagnosis is discussed.

Dynamic performance of microelectromechanical systems deformable mirrors for use in an active/adaptive two-photon microscope.

Active optics such as deformable mirrors can be used to control both focal depth and aberrations during scanning laser microscopy. If the focal depth can be changed dynamically during scanning, then imaging of oblique surfaces becomes possible. If aberrations can be corrected dynamically during scanning, an image can be optimized throughout the field of view. Here, we characterize the speed and dynamic precision of a Boston Micromachines Corporation Multi-DM 140 element aberration correction mirror and a Revibro Optics 4-zone focus control mirror to assess suitability for use in an active and adaptive two-photon microscope. Tests for the multi-DM include both step response and sinusoidal frequency sweeps of specific Zernike modes (defocus, spherical aberration, coma, astigmatism, and trefoil). We find wavefront error settling times for mode amplitude steps as large as 400 nm to be less than 52???s, with 3 dB frequencies ranging from 6.5 to 10 kHz. The Revibro Optics mirror was tested for step response only, with wavefront error settling time less than 80???s for defocus steps up to 3000 nm, and less than 45???s for spherical aberration steps up to 600 nm. These response speeds are sufficient for intrascan correction at scan rates typical of two-photon microscopy.

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.

Real-time digitization of metabolomics patterns from a living system using mass spectrometry.

The real-time quantification of changes in intracellular metabolic activities has the potential to vastly improve upon traditional transcriptomics and metabolomics assays for the prediction of current and future cellular phenotypes. This is in part because intracellular processes reveal themselves as specific temporal patterns of variation in metabolite abundance that can be detected with existing signal processing algorithms. Although metabolite abundance levels can be quantified by mass spectrometry (MS), large-scale real-time monitoring of metabolite abundance has yet to be realized because of technological limitations for fast extraction of metabolites from cells and biological fluids. To address this issue, we have designed a microfluidic-based inline small molecule extraction system, which allows for continuous metabolomic analysis of living systems using MS. The system requires minimal supervision, and has been successful at real-time monitoring of bacteria and blood. Feature-based pattern analysis of Escherichia coli growth and stress revealed cyclic patterns and forecastable metabolic trajectories. Using these trajectories, future phenotypes could be inferred as they exhibit predictable transitions in both growth and stress related changes. Herein, we describe an interface for tracking metabolic changes directly from blood or cell suspension in real-time.

A handheld laser scanning confocal reflectance imaging-confocal Raman microspectroscopy system.

Confocal reflectance microscopy and confocal Raman spectroscopy have shown potential for non-destructive analysis of samples at micron-scale resolutions. Current studies utilizing these techniques often employ large bench-top microscopes, and are not suited for use outside of laboratory settings. We have developed a microscope which combines laser scanning confocal reflectance imaging and confocal Raman spectroscopy into a compact handheld probe that is capable of high-resolution imaging and spectroscopy in a variety of settings. The compact size of the probe is largely due to the use of a MEMS mirror for beam scanning. The probe is capable of axial resolutions of up to 4 µm for the confocal imaging channel and 10 µm for the confocal Raman spectroscopy channel. Here, we report instrument design, characterize optical performance, and provide images and spectra from normal skin to demonstrate the instrument's capabilities for clinical diagnostics.

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 mirror's small size (1.4 mm x 1 mm) will allow integration with endoscopic MEMS-DOCT for in vivo applications.