We present a straightforward approach to making sensitive fluorescence measurements using a chopped laser and phase-lock detection scheme. By using high-quality optical filters in the excitation and detection paths, the trade-off between spectral information and ultimate sensitivity is controlled by the choice of filter edge locations and bandwidths. Using this approach, we demonstrate a sensitivity of ~1 pW optical power of detected fluorescence over a bandwidth of ~125 nm centered at 505 nm using a 405 nm diode laser as an excitation source. We present the details of the measurement technique and discuss its value in selection of optical materials for fluorescence-based analytical systems.
Phase aberration induced by optical coatings can be a critical factor in image quality. When multilayer thin film high reflectors are used at oblique incidence, the two planes of polarization for the most part have different phase shift. This difference is known as phase retardance and is a function of the angle of incidence, coating design, and the spectral wavelength. Point spread function (PSF) calculation by geometrical ray tracing shows the phase aberration caused by the coating could influence the resolution of the lens system. In this paper we investigate phase retardance of three high reflector coating types and their impact on the final image quality in a Schwarzschild objective.
Polarization sensitive optical systems may contain optical components that are considered non-polarization optics, such
as multi-element collection/illumination lenses, relay lenses and focusing/imaging lenses. With conventional optical
design and optomechanical software tools to design these lenses, special consideration is required in choosing glass
materials, coatings, and optomechanical design for low intrinsic and stress-induced birefringence and thermal stability.
Optical design parameters are discussed to achieve overall minimum birefringence, by optimizing with low intrinsic
birefringence glass material, applying phase-controlled (balanced) coating design, and low stress mechanical design
approaches. Also discussed are options for matching thermal expansion coefficient (CTE) of the system components.
Analysis on transmissive phase retardation of a microbjective at its pupil plane, as well as its birefringence
measurement data, will be presented. It is shown that it is critical to design and optimize at multiple positions across the
lens pupil to achieve better polarization performance.
Thin films of titanium, zirconium, and hafnium nitride are prepared by DC magnetron reactive sputtering at room temperature on fused silica, optical glass and silicon substrates. Deposition parameters are investigated in order to obtain stoichiometric films. The optical and electrical properties of the films as a function of nitrogen partial pressure are determined. The results show that an inverse correlation exists between the optical reflectance and the electrical resistivity of the films. The optical constants of the films are determined by Variable Angle Spectroscopic Ellipsometry (VASE) measurements from 240- 1700 nm at 10 nm steps. Deposited film composition is obtained by the Rutherford Ion Back Scattering (RBS) method. The rms roughness of the films is measured by using an optical scatterometer. Ellipsometer data for all three films show that their refractive index (n) in the visible spectrum is decreased by increasing the film thickness while the extinction coefficient (k) is unchanged. Thin films of TiN have the lowest room temperature resistivity (approximately equals 75 (mu) (Omega) - cm) relative to ZrN and HfN thin films.
Thin films of gold and platinum have been deposited onto super-polished fused silica substrates using thermal evaporation, ion assisted deposition (IAD), sputtering and ion assisted sputtering. The influence of ion beam flux, coating material and deposition rate on the films microroughness have been investigated. Coatings of gold and platinum have been bombarded with low energy (10-20 eV) Ar ions from an electron cyclotron resonance (ECR) ion source during deposition. Short range surface microroughness of coated surfaces has been examined using scanning tunneling microscopy (STM) and atomic force microscopy (AFM), while long range surface microroughness has been characterized using an angle resolved optical scatterometer. Results indicate that bombardment with low energy ions cause significant reduction in microroughness of metal coatings.
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