Comparative Study of Some Fiber-Optic Remote Raman Probe Designs. Part II: Tests of Single-Fiber, Lensed, and Flat- and Bevel-Tip Multi-Fiber Probes

1996 ◽  
Vol 50 (7) ◽  
pp. 849-860 ◽  
Author(s):  
Thomas F. Cooney ◽  
H. Trey Skinner ◽  
S. M. Angel
Keyword(s):  
Fiber Optic ◽  
Focal Point ◽  
Focal Length ◽  
Numerical Aperture ◽  
Optical Filters ◽  
Organic Liquids ◽  
Raman Signal ◽  
Immersion Medium ◽  
Lens Focal Length ◽  
Overlap Model

We compare relative performances of flat-tipped, beveled (two-fiber and six-around-one), and single-lensed focused fiber-optic Raman probes and, where feasible, evaluate the utility of optical filters for reducing fiber background. The sensitivity profile of each probe is determined by measuring the relative intensity of light backscattered off a flat surface as a function of distance from the probe tip. The experimental results are compared with a simple light-cone-overlap model incorporating fiber numerical aperture, fiber and immersion medium refractive indices, separation between excitation and collection fibers, number of fibers, and fiber bevel angle and/or lens focal length. The model and sensitivity profiles are used to interpret the sampling regions for Raman spectra obtained by using each of the probes with a clear, transparent sample (single-crystal sparry calcite), a white, partially transparent sample (acetaminophen tablet), and a set of organic liquids of varying refractive index. The sensitivity of the tested commercial lensed probe drops off symmetrically about the focal point. For both solid samples, the intensity of fiber background follows a profile determined primarily by laser backscattering off the surface, whereas the sample Raman signal follows a profile dependent upon sampling depth.

Comparative Study of Some Fiber-Optic Remote Raman Probe Designs. Part I: Model for Liquids and Transparent Solids

1996 ◽  
Vol 50 (7) ◽  
pp. 836-848 ◽  
Author(s):  
Thomas F. Cooney ◽  
H. Trey Skinner ◽  
S. M. Angel
Keyword(s):  
Fiber Optic ◽  
Numerical Aperture ◽  
Signal Strength ◽  
Single Fiber ◽  
Raman Signal ◽  
Excitation Light ◽  
Immersion Medium ◽  
Sampling Volume ◽  
Restricted Volume ◽  
Raman Probe

We have developed models describing the sensitivity and sampling volume of various remote fiber-optic Raman probes—single-fiber, lensed, dual-fiber beveled-tip, dual-fiber flat-tipped, and multi-fiber flat-tipped. The models assume clear samples and incorporate radii, separation, bevel angle, and numerical aperture of the fibers; overlap geometry of illumination and excitation light cones; and refractive index of immersion medium. For the Raman spectra of solid samples in air, single-fiber and lensed probes are predicted to yield the highest Raman signal. Beveled probes should provide greater Raman signal strength than do flat-tipped probes because beveled probes can collect light from a restricted volume closer to the probe end. Although multiple collection fibers improve Raman signal strength, progressively distant concentric fiber rings contribute less and sample material further from the probe.

Electrostatic optics and aberration correction in the 1940s and today

1992 ◽  
Vol 50 (1) ◽  
pp. 6-7
Author(s):  
Gertrude F. Rempfer
Keyword(s):  
Electron Microscope ◽  
Focal Point ◽  
Focal Length ◽  
High Vacuum ◽  
Electron Optics ◽  
Applied Physics ◽  
Electrostatic Lenses ◽  
Commercial Instrument ◽  
The University ◽  
Theory And Experiment

I became involved in electron optics in early 1945, when my husband Robert and I were hired by the Farrand Optical Company. My husband had a mathematics Ph.D.; my degree was in physics. My main responsibilities were connected with the development of an electrostatic electron microscope. Fortunately, my thesis research on thermionic and field emission, in the late 1930s under the direction of Professor Joseph E. Henderson at the University of Washington, provided a foundation for dealing with electron beams, high vacuum, and high voltage.At the Farrand Company my co-workers and I used an electron-optical bench to carry out an extensive series of tests on three-electrode electrostatic lenses, as a function of geometrical and voltage parameters. Our studies enabled us to select optimum designs for the lenses in the electron microscope. We early on discovered that, in general, electron lenses are not “thin” lenses, and that aberrations of focal point and aberrations of focal length are not the same. I found electron optics to be an intriguing blend of theory and experiment. A laboratory version of the electron microscope was built and tested, and a report was given at the December 1947 EMSA meeting. The micrograph in fig. 1 is one of several which were presented at the meeting. This micrograph also appeared on the cover of the January 1949 issue of Journal of Applied Physics. These were exciting times in electron microscopy; it seemed that almost everything that happened was new. Our opportunities to publish were limited to patents because Mr. Farrand envisaged a commercial instrument. Regrettably, a commercial version of our laboratory microscope was not produced.

scholarly journals Evaluating effects of focal length and viewing angle in a comparison of recent face landmark and alignment methods

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Xiang Li ◽  
Jianzheng Liu ◽  
Jessica Baron ◽  
Khoa Luu ◽  
Eric Patterson
Keyword(s):  
Focal Length ◽  
Ground Truth ◽  
Detection Methods ◽  
Viewing Angle ◽  
Deep Convolutional Neural Networks ◽  
Landmark Detection ◽  
High Performing ◽  
Detection Techniques ◽  
And Performance ◽  
Lens Focal Length

AbstractRecent attention to facial alignment and landmark detection methods, particularly with application of deep convolutional neural networks, have yielded notable improvements. Neither these neural-network nor more traditional methods, though, have been tested directly regarding performance differences due to camera-lens focal length nor camera viewing angle of subjects systematically across the viewing hemisphere. This work uses photo-realistic, synthesized facial images with varying parameters and corresponding ground-truth landmarks to enable comparison of alignment and landmark detection techniques relative to general performance, performance across focal length, and performance across viewing angle. Recently published high-performing methods along with traditional techniques are compared in regards to these aspects.

Absorption efficiency analysis and optical resonator simulation of Ho:YLF laser pumped with Tm:fiber laser

Laser Physics ◽  
2021 ◽  
Vol 32 (1) ◽  
pp. 015001
Author(s):  
Majid Babaiy Tooski ◽  
Abbas Maleki ◽  
Abdolah Eslami Majd ◽  
Hassan Ebadian
Keyword(s):  
Slope Efficiency ◽  
Doping Concentration ◽  
Continuous Wave ◽  
Focal Length ◽  
Beam Width ◽  
Absorption Efficiency ◽  
Optical Resonator ◽  
Threshold Power ◽  
Continuous Wave Operation ◽  
Lens Focal Length

Abstract In this paper, a Tm:fiber laser pumped Ho:YLF laser is simulated. The absorption efficiency, optimum crystal length, and optical resonator are analytically studied and simulated using LASCAD software, and the atomic-level degeneracies are considered in evaluating the absorption efficiency. In this way, the absorption efficiencies of 65% and 87% are obtained for single-pass 30 mm Ho:YLF crystal with doping concentration 0.5% and 1% respectively. These calculated efficiencies are verified by our experimental measurements and they coincide with acceptable errors. To estimate a proper length for the Ho:YLF crystal with specified doping concentration, the up-conversion, and the reabsorption effects are considered. As a result, we find the 30 mm length crystal is suited for reducing the absorption threshold and prohibiting reabsorption while saturation is controlled. The threshold power and slope efficiency for 65 W pumped powers are calculated by LASCAD software, and the thermal lens focal length of −665 mm is obtained. For a nearly constant beam width inside the cavity and suitable beam overlap efficiency, a concave-concave configuration is chosen for the optical resonator. In the continuous-wave operation, the output power is funded to be 38.4 W and the slope efficiency would be 66%.

Measurement of Lens Focal Length with Hartmann-Shack Wave Front Sensor Based on 4F System

Applied laser ◽  
2013 ◽  
Vol 33 (2) ◽  
pp. 212-215
Author(s):  
许江华 Xu Jianghua ◽  
朱岚 Zhu Lan ◽  
陈家璧 Chen Jiabi ◽  
庄松林 Zhuang Songlin
Keyword(s):  
Wave Front ◽  
Focal Length ◽  
Lens Focal Length

scholarly journals Polarization Dependence of Low-Frequency Vibrations from Multiple Faces in an Organic Single Crystal

Crystals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 425 ◽  
Author(s):  
Nemtsov ◽  
Aviv ◽  
Mastai ◽  
Tischler
Keyword(s):  
Raman Spectroscopy ◽  
Intermolecular Interactions ◽  
Signal Intensity ◽  
Structural Information ◽  
Low Frequency ◽  
Incident Beam ◽  
Optical Filters ◽  
Polarization Dependence ◽  
Raman Signal ◽  
Shear Modes

Recent developments in optical filters have enabled the facile use of Raman spectroscopy for detection of low frequency (LF) vibrational modes. LF-Raman spectroscopy offers fast and sensitive characterization of LF vibrations, and enables the measurement of single microcrystals and detection of defects. It is useful for probing intermolecular interactions in crystals, which are lower in energy, such as hydrogen bonds, shear modes, and breathing modes. Crystal excitation from multiple faces allows learning the orientation of intermolecular interactions, as polarization dependence varies with the polarizability of the interactions along the planes. Elucidating the orientations of the intermolecular interactions in organic crystals is essential for guiding the reactions or adsorption to a specific crystal face. In this study, we investigated the dependence of the LF-Raman signal intensity on the orientation of an organic single microcrystal of L-alanine. Three incident beam directions provided the orientations of the intermolecular interactions by analyzing the corresponding LF-Raman spectra. The signal intensity correlated well with the proximity between the incident beam’s direction and the orientations of the intermolecular interactions. Excellent compatibility was found between the spectra and simulated orientations based on structural information.

scholarly journals Implementation and Optimization of a Dual-confocal Autofocusing System

Sensors ◽  
2020 ◽  
Vol 20 (12) ◽  
pp. 3479
Author(s):  
Chia-Ming Jan ◽  
Chien-Sheng Liu ◽  
Jyun-Yi Yang
Keyword(s):  
Focal Point ◽  
Focal Length ◽  
Characteristic Curve ◽  
Polynomial Equation ◽  
Systematic Design ◽  
Focal Position ◽  
Exact Position ◽  
Time Position ◽  
Major Factors ◽  
Auto Focusing

This paper describes the implementation and optimization of a dual-confocal autofocusing system that can easily describe a real-time position by measuring the response signal (i.e., intensity) of the front and the rear focal points of the system. This is a new and systematic design strategy that would make it possible to use this system for other applications while retrieving their characteristic curves experimentally; there is even a good chance of this technique becoming the gold standard for optimizing these dual-confocal configurations. We adopt two indexes to predict our system performance and discover that the rear focal position and its physical design are major factors. A laboratory-built prototype was constructed and demonstrated to ensure that its optimization was valid. The experimental results showed that a total optical difference from 150 to 400 mm significantly affected the effective volume of our designed autofocusing system. The results also showed that the sensitivity of the dual-confocal autofocusing system is affected more by the position of the rear focal point than the position of the front focal point. The final optimizing setup indicated that the rear focal length and the front focal length should be set at 200 and 100 mm, respectively. In addition, the characteristic curve between the focus error signal and its position could successfully define the exact position by a polynomial equation of the sixth order, meaning that the system can be straightforwardly applied to an accurate micro-optical auto-focusing system.

Determination of Geometric Distortions in Automotive Lamps Using Non-Linear Parametric Estimations

2002 ◽  
Author(s):  
Asad A. Usman ◽  
Mohammad Usman
Keyword(s):  
Motor Vehicle ◽  
Focal Point ◽  
Focal Length ◽  
Parametric Estimation ◽  
Geometric Distortions ◽  
Reflected Light ◽  
Non Linear ◽  
Gauss Method ◽  
Reflector Geometry

In automotive lamps, an ideal paraboloid is the reflector shape of choice when lens optics is utilized. However, geometric distortions occur among manufactured automotive lamps. This paper discusses the effects of geometric distortions on spread, packing, and gradient of reflected light from automotive lamps. Relevant legal requirements set by Federal Motor Vehicle Safety Standard on the performance of automotive lamps are also discussed. A new parametric mathematical model is developed to represent the geometry of an ideal lamp reflector. A non-linear parametric estimation problem is formulated using the Box-Kanemasu modification of the Gauss method. An application of methodology is also presented in this paper. The results show significant distortions of paraboloidal reflector with respect to the ideal design-intent reflector geometry. The numerically calculated deviations of focal point, focal length and paraboloidal axis from the ideally designed reflector necessitate improvements in the tooling and the manufacturing process for better dimensional control.

Wave Height Measurements Behind Submerged Lens-Shaped Structures

2011 ◽  
Author(s):  
Andrew L. Bloxom ◽  
Karl D. von Ellenrieder ◽  
Matthew R. Anderson ◽  
Ryan S. Mieras ◽  
William S. Weidle
Keyword(s):  
Wave Height ◽  
Focal Point ◽  
Focal Length ◽  
Experimental Tests ◽  
Geometrical Optics ◽  
Width Ratio ◽  
Focal Points ◽  
Wave Amplification ◽  
Strip Theory ◽  
Longitudinal Position

The ability of submerged lens-shaped structures to focus linear surface waves in deep water is explored through a series of experimental tests in a wave making basin. Three lenses were designed using a combination of linear strip theory and a surface wave analogy to geometrical optics. Two of these lenses were designed to focus waves of a single wavelength of 0.482 m (18.97 in.), one with a focal length to lens width ratio (f-number) of 2.0 and the other with an f-number of 0.5. The third lens was designed to function as a compound lens that could focus a range of wavelengths of between 0.39 m (15.37 in.) and 0.694 m (27.32 in.) at an f-number of 2.0. Using resistance wave height gauges, the sensitivity of wave height at the focus to variations in wavelength from between 0.39 m (15.37 in.) to 0.61 m (24.01 in.) was experimentally measured for all three lenses; the sensitivity of wave height at the focus to variations of lens depths of submergence spanning the range of between 0.75 to 1.25 times the design submergence depth was also explored for the two simple lenses. It was found that the linear strip theory and geometrical optics approach predicted the wave amplification to within ten percent at the design wavelengths and depths, but that the longitudinal position of the experimentally observed focal lengths differed substantially from that expected, by as much as a factor of 2.2 for an f-number of 0.5. Additionally, while the theory predicted a single focal point for each lens, multiple focal points were found to exist behind the compound lens.

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