Phase shift of amplitude-modulated optical signals in graphene oxide water dispersions due to thermal lens focal length oscillation

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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The interferometric measurement of thermal lens effect in a LD pumped Tm-doped bulk laser

Applied Physics Express ◽

10.35848/1882-0786/ac3ea9 ◽

2021 ◽

Author(s):

Yuantao Zhao ◽

Shengzhi Zhao ◽

Tao Li ◽

Yizhou Liu ◽

Chun Wang ◽

...

Keyword(s):

Temperature Distribution ◽

Thermal Lens ◽

Precise Measurement ◽

Laser Crystal ◽

Focal Length ◽

Mode Locking ◽

Experimental Result ◽

Interferometric Method ◽

Thermal Lens Effect ◽

Thermal Focal Length

Abstract Directly measuring thermal focal length is important for designing and optimizing the mode locking oscillator, especially for a 2-μm mode-locking laser. In this paper, we propose a novel interferometric method for measuring the thermal focal length in a 2-μm mode-locking laser. This method could give a precise measurement of the thermal focal length inside a long-folded oscillator in both lasing and non-lasing operation. We also theoretically calculate the thermal focal length based on the temperature distribution inside the laser crystal, which matches well with the experimental result

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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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