The Effect of the Convex Lens Focal Length and Distance Between the Optical Devices on the Photoacoustic Signals in Gas Detection

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.

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

Laser Physics ◽

10.1088/1555-6611/ac3b46 ◽

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%.

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

Applied laser ◽

10.3788/al20133302.212 ◽

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

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Transparent Object Shape Measurement Based on Deflectometry

Proceedings ◽

10.3390/icem18-05428 ◽

2018 ◽

Vol 2 (8) ◽

pp. 548

Author(s):

Zhichao Hao ◽

Yuankun Liu

Keyword(s):

Data Acquisition ◽

Phase Measurement ◽

Focal Length ◽

Three Dimensional ◽

Normal Direction ◽

Calibration Data ◽

Actual Measurement ◽

Temporal Phase ◽

Convex Lens ◽

Normal Orientation

This paper proposes a method for obtaining surface normal orientation and 3-D shape of plano-convex lens using refraction stereo. We show that two viewpoints are sufficient to solve this problem under the condition that the refractive index of the object is known. What we need to know is that (1) an accurate function that maps each pixel to the refraction point caused by the refraction of the object. (2) light is refracted only once. In the simulation, the actual measurement process is simplified: light is refracted only once; and the accurate one-to-one correspondence between incident ray and refractive ray is realized by known object points. The deformed grating caused by refraction point is also constructed in the process of simulation. A plano-convex lens with a focal length of 242.8571 mm is used for stereo data acquisition, normal direction acquisition, and the judgment of normal direction consistency. Finally, restoring the three-dimensional information of the plano-convex lens by computer simulation. Simulation results suggest that our method is feasibility. In the actual experiment, considering the case of light is refracted more than once, combining the calibration data acquisition based on phase measurement, phase-shifting and temporal phase-unwrapping techniques to complete (1) calibrating the corresponding position relationship between the monitor and the camera (2) matching incident ray and refractive ray.

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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

Applied Spectroscopy ◽

10.1366/0003702963905574 ◽

1996 ◽

Vol 50 (7) ◽

pp. 849-860 ◽

Cited By ~ 41

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.

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Numerical Simulations of Fractional Fourier Transform of Hypergeometric-Gaussian Beam

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.765-767.780 ◽

2013 ◽

Vol 765-767 ◽

pp. 780-784 ◽

Cited By ~ 2

Author(s):

Zhen Feng Yang ◽

Wen Dan Miao ◽

Zhen Jun Yang ◽

Shu Min Zhang

Keyword(s):

Fourier Transform ◽

Numerical Simulations ◽

Gaussian Beam ◽

Intensity Distribution ◽

Fractional Fourier Transform ◽

Focal Length ◽

Beam Width ◽

Laser Beams ◽

New Type ◽

Lens Focal Length

The fractional Fourier transform (FRFT) of a new type of laser beams called the hypergeometric-Gaussian beam (HyGGB) is investigated in detail. The analytical expression for the FRFT of a HyGGB is derived. The properties of a HyGGB in the FRFT plane with different parameters are illustrated. The results show that the intensity distribution of a HyGGB in the FRFT plane strongly depends on the fractional order, the lens focal length and the initial beam width.

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Design of the Real-Time Autofocusing System for Collimator with Long Focus Length and Large Aperture

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.127.25 ◽

2011 ◽

Vol 127 ◽

pp. 25-31

Author(s):

Xiang Li ◽

Xiao Hui Zhang

Keyword(s):

Computer Simulation ◽

Semiconductor Lasers ◽

Essential Role ◽

Focal Length ◽

Optical Devices ◽

Plane Mirror ◽

Large Aperture ◽

Surrounding Environment ◽

New Type ◽

Common Problems

Large aperture collimator which has been widely used for calibrating and testing various optical devices plays an essential role in correlative laboratories. As being the basic testing and calibration equipment, the large aperture collimator’s accuracy should be much higher than the device under testing in order to ensure the accuracy of the measurement. However, the process of adjusting the collimator is extremely complicated due to the collimator’s large aperture and long focal length. So it is difficult to ensure the measurement’s quality and easy to cause the system being vulnerable to the surrounding environment. One of the most common problems is defocus. In order to solve the problem above, this issue presents a new type of autocollimator autofocusing system which uses pentaprism instead of using large-aperture plane mirror, semiconductor lasers as light source and CCD sensor as receiver. The system is smaller, lighter, and more convenient when using. The computer simulation shows that the autofocusing system’s resolution could reach the accuracy of 40μm. If we use the relevant algorithms to execute the sub-pixel scanning, the resolution could reach the accuracy of 10μm. It shows that the system could satisfy the required testing precision of testing large aperture optical device.

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