An echelle spectrograph can provide high resolving power (wavelength/FWHM) across a broad spectral range. These optical instruments are commonly used in spectroscopy for atomic and molecular identification in astronomical observations and laboratory analysis. The wavelength range of an echelle spectrograph is ultimately limited by the capabilities of the detector used to acquire the spectral data. Silicon based CCD, EMCCD and CMOS sensors typically enable measurements from 200nm to 1100nm. Infrared Laboratories and Catalina Scientific Instruments (CSI) have collaborated to demonstrate an application that combines IR Lab’s TRIWAVE camera with CSI’s EMU120/65 echelle spectrograph. The TRIWAVE camera covers a spectral range of 300nm to 1600nm, greatly increasing the wavelength range for applications using the EMU-120/65 spectrograph. With this increased capability, an opportunity exists for measuring the dielectric coating thickness of thin film by extracting and analyzing interference fringes from the spectral data. Methods and results of this measurement will be presented.
Visible-band cameras using silicon imagers
provide excellent video under daylight
conditions, but become blind at night. The
night sky provides illumination from 1-2 μm
which cannot be detected with a silicon sensor.
Adding short-wave infrared detectors to a
CMOS imager would enable a camera which
can be used day or night.
A germanium-enhanced CMOS imager
(TriWave®) has been developed with
broadband sensitivity from 0.4 μm to 1.6 μm.
A 744 x 576 format imager with 10 μm pixel
pitch provides a large field of view without
incurring a size and weight penalty in the
optics. The small pixel size is achieved by
integrating a germanium photodetector into a
mainstream CMOS process. A sensitive
analog signal chain provides a noise floor of 5
electrons. The imagers are hermetically
packaged with a thermo-electric cooler in a
windowed metal package 5 cm3 in volume. A
compact (<650 cm3) camera core has been
designed around the imager. Camera
functions implemented include correlated
double sampling, dark frame subtraction and
In field tests, videos recorded with different
filters in daylight show useful fog and haze
penetration over long distances. Under clear
moonless conditions, short-wave infrared
(SWIR) images recorded with TriWave make
visible individuals that cannot be seen in
videos recorded simultaneously using an
EMCCD. Band-filtered videos confirm that
the night-sky illumination is dominated by
wavelengths above 1200 nm.
Recently, a number of research groups around the world have developed ophthalmic instruments capable of in vivo diffraction limited imaging of the human retina. Adaptive optics was used in these systems to compensate for the optical aberrations of the eye and provide high contrast, high resolution images. Such compensation uses a wavefront sensor and a wavefront corrector (usually a deformable mirror) coordinated in a closed- loop control system that continuously works
to counteract aberrations. While those experiments produced promising results, the deformable mirrors have had insufficient range of motion to permit full correction of the large amplitude aberrations of the eye expected in a normal population of human subjects. Other retinal imaging systems developed to date with MEMS (micro-electromechanical
systems) DMs suffer similar limitations.
This paper describes the design, manufacture and testing of a 6um stroke polysilicon surface micromachined deformable mirror that, coupled with an new optical method to double the effective stroke of the MEMS-DM, will permit diffraction-limited retinal imaging through dilated pupils in at least 90% of the human population. A novel optical design using spherical mirrors provides a double pass of the wavefront over the deformable mirror such that a 6um mirror
displacement results in 12um of wavefront compensation which could correct for 24um of wavefront error. Details of this design are discussed. Testing of the effective wavefront modification was performed using a commercial wavefront sensor. Results are presented demonstrating improvement in the amplitude of wavefront control using an existing high degree of freedom MEMS deformable mirror.