Ultrafast Laser Induced Structural Modification of Fused Silica—Part II: Spatially Resolved and Decomposed Raman Spectral Analysis

Vukelić, Siniša; Kongsuwan, Panjawat; Ryu, S.-R.; Yao, Y. Lawrence

doi:10.1115/1.4002768

Cited by 10 publications

(12 citation statements)

References 27 publications

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“…To evaluate the amount of various ring structures in the network of silica glass formed by silicon and oxygen atoms, the obtained Raman spectra were fitted by three Lorentzian function series, which correspond to the ½ 1 band (five-and six-membered rings), D 1 band (four-membered ring), and D 2 band (three-membered ring), respectively, as given by: 13) …”

Section: Micro-raman Spectroscopy Of Asymmetric δN Structurementioning

confidence: 99%

Large increase in refractive index inside silica glass after the movement of voids caused by femtosecond laser pulses

Hashimoto¹,

Yoshino²,

Ozeki³

et al. 2014

Jpn. J. Appl. Phys.

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When a transparent material is irradiated by focused femtosecond laser pulses, various types of structural modification can occur inside the material. Recently, it has been reported that asymmetric structures, which are composed of two regions with positive and negative refractive index changes (Δn), can be inscribed by irradiation of multiple femtosecond laser pulses at high (>MHz) repetition rates. Interestingly, the amount of positive Δn in this type of modification is larger than those in conventional structural modifications by one order of magnitude. However, the mechanisms underlying such modifications are still unclear. In this paper, we describe that similar asymmetric structures can be inscribed by using femtosecond laser pulses at a low repetition rate. Then, we examine the formation and spectroscopic characteristics of the asymmetric structures. The observation of the processed areas reveals that the asymmetric structures are formed after the movement of voids. Furthermore, micro-Raman spectroscopy suggests a large increase of three-membered ring structures in the region with positive Δn, which may account for the large Δn.

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Section: Micro-raman Spectroscopy Of Asymmetric δN Structurementioning

confidence: 99%

Large increase in refractive index inside silica glass after the movement of voids caused by femtosecond laser pulses

Hashimoto¹,

Yoshino²,

Ozeki³

et al. 2014

Jpn. J. Appl. Phys.

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“…From this figure, it can also be observed that [43]. Figure 10: Volume fraction distribution of (a) five-and sixmembered rings based on the 440 cm-1 peak, (b) fourmembered rings based on the 495 cm-1 peak, and (c) threemembered rings based on the 606 cm-1 peak in Raman spectra of cross section of laser-irradiated region (pulse energy of 30 μJ and federates of 0.04 mm/s) [39].…”

Section: Weld Formation and Geometrymentioning

confidence: 94%

“…Decomposition of the Raman spectra in the region between wavenumbers 300 cm -1 and 630 cm -1 , where three distinctive peaks corresponding to the different ring structures were observed, was performed through a curve fitting process [39]. It is assumed that within the volume of interest four different structures coexist three-, four-, five-and six-membered rings.…”

Section: Changes In Ring Structures and Their Volume Fractions By Rammentioning

confidence: 99%

“…Figure 15 shows the indentation fracture toughness of material inside the weld seam compared to the reference material, and also shows the effect of laser pulse energy on the fracture toughness. In the ultrafast laser-treated region, there are more nonbridging oxygen hole centers (NBOHCs) [33] and the connectivity of the structure is decreased, and at the same time the remaining connected ring structures of material become more compact [39]. The presence of NBOHCs may help branch the main crack while a higher driving force is required to propagate the main crack through the more compact ring structure.…”

Section: Fracture Toughness and Fracture Strength Of The Weld Seammentioning

confidence: 99%

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Structuring and joining transparent materials with ultra short pulse lasers

Kongsuwan¹,

Vukelić²,

Yao³

2013

International Congress on Applications of Lasers &Amp; Electro-Optics

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Nonlinear absorption of femtosecond-laser pulses enables the induction of structural changes in the interior of bulk transparent materials without affecting their surface. Features are generated by focusing the femtosecond laser pulses in the interior of a single glass piece to investigate change in morphology, mechanical properties, and ring structures of the modified region. Detailed characterization of the effect of laser irradiation is accomplished using differential interference contrast optical microscopy, spatially resolved Raman spectroscopy, and spatially resolved nanoindentation. A numerical model is also developed to predict an absorption volume inside transparent dielectric materials. After the better understanding of effects of optical and laser processing parameters on the resultant features is developed, the femtosecond laser pulses are finally focused on the interface of two glass specimens to implement transmission welding. The weld formation and geometry are discussed and indentation fracture analysis is used to investigate the strength of the weld seams.

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“…Cross sections of induced features are examined via decomposition of the spatially resolved Raman spectra and quantitative characterization of the structure of amorphous fused silica is developed. This method identifies the volume fraction distribution of ring structures and changes of the distribution with laser process conditions [12]. Fractional wavelet transform (FWT) is a powerful tool to extract largest analytical information from the spectral bands.…”

Section: Introductionmentioning

confidence: 99%

Spectral feature extraction and characterization via simple linear and nonlinear technology integration

Ye¹,

Mohamadian²

2011

2011 IEEE 12th International Symposium on Computational Intelligence and Informatics (CINTI)

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A systematic approach for spectral calibration, extraction and characterization is presented. It involves the simple technology integration of the linear and nonlinear methodologies. Raman spectra are essentially weak signals whose features are sensitive to a variety of noises, while the background spectra (e.g., fluorescence spectra) act as another primary intensity component in the raw Raman spectrograph. Thus the calibrated Raman spectra from measurements are subject to detrend and denoising so as to extract the intrinsic spectra, which contain solely the unique spectral signatures of the individual biomedical samples. By removing the slowly varying baseline background spectra and rapidly varying noises, intrinsic Raman spectra could be extracted using a combination of linear and nonlinear methodologies. The goal is to capture the distinguishable wave number information on the Raman shift for feature identification. This approach is crucial for spectra analysis to associate Raman spectra with the medical diagnosis. Considering the slowly varying nature of background spectra such as fluorescence, linear least squares estimation is applied to detrend the background spectra from the measured spectra being calibrated. Since most noises are rapidly varying, nonlinear discrete wavelet transform (DWT) denoising is applied to separate the intrinsic Raman spectra from noises for spectral identification. This approach is proposed so as to differentiate the normal spectra from the abnormal spectra of the fresh mice lung samples. Numerical simulation outcomes include the calibrated Raman spectra, detrended spectra free of background effects and the extracted intrinsic spectra after nonlinear DWT denoising. The satisfactory results indicate that the proposed simple linear and nonlinear technology integration provides a useful approach for biomedical sample characterization. In addition, it reduces computational complexity compared with artificial intelligence approaches, which has no technical difficulty in real time medical diagnosis implementation. This serves as a fundamental step for further data clustering and accurate decision making among numerous diverse samples.

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Ultrafast Laser Induced Structural Modification of Fused Silica—Part II: Spatially Resolved and Decomposed Raman Spectral Analysis

Cited by 10 publications

References 27 publications

Large increase in refractive index inside silica glass after the movement of voids caused by femtosecond laser pulses

Large increase in refractive index inside silica glass after the movement of voids caused by femtosecond laser pulses

Structuring and joining transparent materials with ultra short pulse lasers

Spectral feature extraction and characterization via simple linear and nonlinear technology integration

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