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Research Papers

Characterization of Morphology and Mechanical Properties of Glass Interior Irradiated by Femtosecond Laser

[+] Author and Article Information
Panjawat Kongsuwan

Department of Mechanical Engineering, Columbia University, New York, NY 10027pk2261@columbia.edu

Hongliang Wang

Department of Mechanical Engineering, Columbia University, New York, NY 10027hw2288@columbia.edu

Sinisa Vukelic

Department of Mechanical Engineering, Bucknell University, Lewisburg, PA 17837sinisa.vukelic@bucknell.edu

Y. Lawrence Yao

Department of Mechanical Engineering, Manufacturing Research Laboratory, Columbia University, New York, NY 10027yly1@columbia.edu

J. Manuf. Sci. Eng 132(4), 041009 (Jul 23, 2010) (10 pages) doi:10.1115/1.4002062 History: Received November 23, 2009; Revised June 21, 2010; Published July 23, 2010; Online July 23, 2010

Femtosecond laser pulses were focused in the interior of a single fused silica piece. Proper use of optical and laser processing parameters generated structural rearrangement of the material through a thermal accumulation mechanism, which could be potentially used for the transmission welding process. The morphology of generated features was studied using differential interference contrast optical microscopy. In addition, the predictive capability of the morphology is developed via a finite element analysis. The change in mechanical properties was studied through employment of spatially resolved nanoindentation. The specimen was sectioned and nanoindents were applied at the cross section to examine mechanical responses of the laser-modified region. Fracture toughness measurements are carried out to investigate the effects of the laser treatment on strength of the glass.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic illustration of experimental setup. The laser beam is focused into the interior of the fused silica sample, and the scanning direction is along the y-axis.

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Figure 2

Transmission DIC optical microscopy of cross section view (x-z plane) of femtosecond laser-irradiated fused silica (beam diameter of 1.5 μm, scanning speed of 0.04 mm/s, and rep rate of 1 kHz)

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Figure 3

Transmission DIC optical microscopy of cross section view (x-z plane) of femtosecond laser-irradiated fused silica (beam diameter of 1.5 μm, pulse energy of 30 μJ, and rep rate of 1 kHz)

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Figure 4

Height, width, and height/width ratio of the feature (affected area as shown in Fig. 2) in femtosecond laser-irradiated fused silica at different pulse energy levels but same scanning speed of 0.04 mm/s. Error bars denote standard deviation.

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Figure 5

Height, width, and height/width ratio of the feature (affected area as shown in Fig. 3) in femtosecond laser-irradiated fused silica at pulse energy level of 30 μJ with various scanning speeds. Error bars denote standard deviation.

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Figure 6

Representative temperature distribution in femtosecond laser-irradiated fused silica at pulse energy level of 30 μJ and scanning speed of 0.04 mm/s. The gray area represents the material region that experiences the temperature equal or greater than the softening point (step time of 520 fs).

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Figure 7

Experimental and numerical feature morphology comparison: (a) feature size (b) height/width ratio of femtosecond laser-irradiated fused silica at different pulse energy levels with the same scanning speed of 0.04 mm/s. Error bars denote standard deviation.

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Figure 8

Representative reflection DIC optical microscopy of spatially resolved nanoindentation array (200 nm depth and 5 μm spacing) on the cross section (x-z plane) of fused silica irradiated by femtosecond laser. The circle locates the weakest point in Young’s modulus and hardness corresponds to Fig. 1.

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Figure 9

Representative load-displacement curves for 200 nm indentation in untreated and irradiated regions of fused silica sample

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Figure 10

Spatially resolved determination of (a) Young’s modulus (b) hardness on the cross section of laser-irradiated region (30 μJ pulse energy and 0.04 mm/s scanning speed). The maps correspond to the array of 200 nm depth nanoindents with 5 μm spacing shown in Fig. 8 and are constructed based on the load-displacement measurement results shown in Fig. 9.

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Figure 11

Spatially resolved determination of the ratio between hardness and Young’s modulus (H/E) on the cross section of laser-irradiated region (30 μJ pulse energy and 0.04 mm/s scanning speed). The maps correspond to the array of 200 nm depth nanoindents with 5 μm spacing shown in Fig. 8 and are constructed based on the load-displacement measurement results shown in Fig. 9.

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Figure 12

Spatially resolved determination of the normalized dissipated energy on the cross section of laser-irradiated region (30 μJ pulse energy and 0.04 mm/s scanning speed). The maps correspond to the array of 200 nm depth nanoindents with 5 μm spacing shown in Fig. 8 and are constructed based on the load-displacement measurement results shown in Fig. 9. The maps represent ductility index and densification.

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Figure 13

Volume fraction distribution of three- and fourfold ring structures based on the 606 cm−1 and 495 cm−1 peaks in Raman spectra of cross section of femtosecond laser-irradiated region (30 μJ pulse energy and 0.04 mm/s scanning speed) (17)

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Figure 14

Maximum decrease of modulus (E), hardness (H), and hardness to modulus ratio (H/E) of 200 nm depth nanoindents inside the femtosecond laser-irradiated regions (same scanning speed of 0.04 mm/s but different pulse energy levels.) Error bars denote standard error.

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Figure 15

Maximum decrease of modulus (E), hardness (H), and hardness to Young’s modulus ratio (H/E) of 200 nm depth nanoindents inside the femtosecond laser-irradiated regions (same pulse energy level of 30 μJ with various scanning speeds). Error bars denote standard error.

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Figure 16

Reflection DIC optical microscopy of 2 μm depth nanoindents on and off the femtosecond laser-irradiated region for fracture toughness measurements

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Figure 17

(a) AFM scan (the derivative of topography) of 2 μm depth indentation. (b) Crack parameters for Berkovich indenter. Crack length c is measured form the center of the residual impression to the tip of crack at specimen surface.

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Figure 18

Comparison of fracture toughness measured by crack-induced indentation method between untreated and irradiated regions at 30 μJ pulse energy with various scanning speeds, and at different pulse energy levels with 0.04 mm/s scanning speed of fused silica sample

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