Laser processing of diamond have attracted attention. Ultrashort laser pulses can be used for micro-structuring on diamond and in bulk diamond. In this paper, we report on laser parameters for surface structuring of diamond by using femtosecond laser pluses at a repetition rate of 1 kHz. By changing scanning speed and energy, different types of grooves were inscribed. The morphology and depth of grooves were investigated.
When ultrashort laser pulses are focused inside a glass at a high repetition rate, structural changes occur because of the heat accumulation from the train of laser pulses. This report describes phase measurement of the structural changes induced inside glass by phase-shifting digital holographic microscopy. Two-dimensional phase distribution across the structural change for static exposure is retrieved. By focusing femtosecond laser pulses at the interface between two glass substrates, melted materials can directly weld glass plates. Quantitative phase measurement of welded glass substrates revealed that the refractive index decreased in the laser-irradiated zone.
We investigated the relationship between size of melting marks formed inside glass and irradiation time and absorptivity of femtosecond laser beam. For this investigation the absorptivities for static exposure in fs-laser processing (femtosecond laser microprocessing inside glass) was estimated to approximately 4.5 [%]. Also the size of melting marks formed by fs-laser processing was measured with two irradiation times (1/125 [s] and 1/4 [s]). The sizes were much the same. Thus, in this time scale, the size was nearly independent of the irradiation time. Furthermore, luminescence phenomenon that occurred in fs-laser processing was observed. The duration of this luminescence was less than 2/1000 [s]. With the above experimental results, we demonstrated numerical heat transfer analysis during the fs-laser processing. From the experimental and numerical results it thought that the most process in fs-laser processing finishes within 2/1000 [s].
In this paper, we present the investigation results on laser-induced structural modifications in a BK7 glass sample
(OHARA, S-BSL7) by use of a femtosecond laser and a CO2 laser system. A femtosecond fiber laser system (wavelength: 1.06 μm, pulse duration: 250 fs) generates 1 MHz ultrashort laser pulses with a pulse energy up to 2 μJ, and a CO2 laser system generates CW (continuous wave) laser beam with a wavelength of 10.6 μm. Both laser beams were simultaneously irradiated on a BK7 glass substrate (30 mm × 5 mm × 0.7 mm thick). The structural modifications regions were created by translating the glass sample perpendicular to the laser axis with a distance of 1 mm and a scan speed of 0.1 mm/s. The dependence of structural modifications on the laser energy of femtosecond laser pulses and the power of CO2 laser beam were investigated. The results have demonstrated that the refractive index change region with the width of 3 μm was created with simultaneously irradiation of two laser beams although the structural modification regions, which were produced with only femtosecond laser pulses, were surface ablation. And the surface ablation regions were changed to the refractive index change regions as the energy of CO2 laser beam increase to more than 2W.
In this paper, we present the investigation results on doping to a BK7 glass sample ( OHARA, S-BSL7 ) by use of a CO2
laser. CO2 laser system generates CW ( continuous wave ) laser beam with a wavelength of 10.6 μm. Laser beam
irradiated on a sample substrate ( 30 mm × 5 mm × 0.67 mm thick ). A surface of the glass was applied fluorescent
material. The doped regions were created by translating the glass sample perpendicular to the laser axis with a distance
of 2 mm and a scan speed of 1 mm/s. After processing, the cross section of sample was analyzed by energy dispersive
X-ray analysis ( EDX ) in scanning electron microscope for revealing the contained elements in the glass. The results
show that carbon was widely distributed in the doped regions although the original glass material did not contain carbon
element.
The present study is undertaken in order to develop an automatic measurement system for light transmissibility of jointed
transparent materials using high-rate-pulses ultrafast laser microwelding. To measure joint strength, it is necessary to
measure the tensile strength and welded area quantitatively. Especially, the welded area greatly influences joint strength
in the microwelding. Thus, it is important to distinguish the welded area and non-welded area. The welded sample was
irradiated by He-Ne laser light, and the light, which passed through the welded sample, was detected by a photo detector.
The transmitted light has two intensity levels because the transmissibly of light is different in the welded area and
non-welded area of the welded sample. Wherein, the welded area and non-welded area are classified by irradiating the
He-Ne light to the sample, and detecting the transmitted light. This technique is also applied to determine the accurate
welded area after welding using various shapes such as spiral and rectangular, the relationship between joint strength and
shapes will be presented.
When ultrafast laser pulses are focused inside the interface between a couple of transparent materials, the optical
intensity in the focal area can usually become high enough to initiate the filamentary propagation of optical pulses and
almost simultaneously the nonlinear absorption occurs in the filamentary area. Due to this absorption of optical energy,
both of the materials can locally be melted and the interface is joined after resolidification. The laser microwelding
technique based on the nonlinear phenomena has several unique features: (i) the insertion of any intermediate layers is no
need for the microwelding, (ii) it's possible to weld the materials with different thermal expansion coefficients, (iii) the
joint area can also be arbitrarily extended by scanning the filamentary area. We call this powerful technique "ultrafast
laser microwelding". In this paper, we present the results on "ultrafast laser microwelding" for transparent materials such
as the silica and borosilicate glass, and heterogeneous materials such as glass and metals.
The micro-welding technique based on the nonlinear absorption via focused femtosecond laser pulses is useful for
welding transparent materials without introducing a light-absorbing intermediate layer. In fact, it has been successful to
weld a wide variety of glass materials using 800-nm or 1045-nm pulses. In this paper, we show that this technique can be
extended to semiconductor materials, which are opaque in the above wavelength regions, by demonstrating the welding
of silicon and borosilicate glass. The key is the use of long-wavelength pulses. We used 1558-nm, 947-fs, 500-kHz
pulses from an amplified femtosecond Er-fiber laser. We used a 20× objective lens with a numerical aperture of 0.40 to
focus the pulses at the interface of silicon and borosilicate glass, which were mounted on a two-dimensional translation
stage. By translating the stage perpendicular to the optical axis in the two-dimensional plane, we produced a 3 × 3 array
that consists of welding areas of 100 &mgr;m × 100 &mgr;m. After welding, we performed a simple tensile test. The joint strength
was found to be 3.74 MPa, which was on the same order as that between borosilicate glasses (9.87 MPa). Although the
welding between silicon substrates is currently hindered by the difficulty of observing focal point with visible light, our
result is an important step toward the welding of semiconductor materials, which may have various applications such as
three-dimensional stack of electronic devices and the fabrication of micro-electro-mechanical systems.
When a femtosecond laser pulse is focused at the interface of two transparent substrates, localized melting and
quenching of the two substrates occur around the focal volume due to nonlinear absorption. The substrates can then be
joined by resolidification of the materials. We demonstrate the joining of similar and dissimilar glass substrates using a
1-kHz 800-nm Ti:sapphire amplifier. We investigated the laser parameter to join transparent substrates and characterized
the joint strength and the transmittance through joint volumes.
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