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Proceedings ArticleDOI

Optical coherence and beamspread in ultrafast-laser pulsetrain-burst hole drilling

08 Sep 2006-Vol. 6343
TL;DR: In this paper, a modified Michelson interferometer was used to measure transverse coherence of the beam as it propagates in a cylindrical channel, and the authors showed that as the beam propagates down the channel, it will decompose over the dispersive waveguide modes, and this will affect the beam coherence, ultimately limiting the maximum depth that the beam can reach.
Abstract: Pulsetrain-burst machining has been shown to have advantages over single-pulse laser processing of materials and biological tissues. Ultrafast lasers are often able to drill holes in brittle and other difficult materials without cracking or swelling the target material, as is sometimes the case for nanosecond-pulse ablation; further, pulsetrain-bursts of ultrafast pulses are able to recondition the material during processing for instance, making brittle materials more ductile and striking advantages can result. In the work we report, we have investigated hole-drilling characteristics in metal and glass, using a Nd:glass pulsetrain-burst laser (1054 nm) delivering 1-10 ps pulses at 133 MHz, with trains 3-15 μs long. We show that as the beam propagates down the channel being drilled, the beam loses transverse coherence, and that this affects the etch-rate and characteristics of channel shape: as the original Gaussian beam travels into the channel, new boundary conditions are imposed on the propagating beam principally the boundary conditions of a cylindrical channel, and also the effects of plasma generated at the walls as the aluminum is ablated. As a result, the beam will decompose over the dispersive waveguide modes, and this will affect the transverse coherence of the beam as it propagates, ultimately limiting the maximum depth that laser-etching can reach. To measure transverse beam coherence, we use a Youngs two-slit interference setup. By measuring the fringe visibility for various slit separations, we can extract the transverse coherence as a function of displacement across the beam. However, this requires many data runs for different slit separations. Our solution to this problem is a novel approach to transverse coherence measurements: a modified Michelson interferometer. Flipping the beam left-right on one arm, we can interfere the beam with its own mirror-image and characterise the transverse coherence across the beam in a single shot.

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Citations
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Patent
01 Aug 2013
TL;DR: An apparatus, method, and process that includes a substantially transparent substrate having a first surface, a second surface, and an edge extending around at least a portion of a perimeter of the transparent substrate, wherein the edge being a laser induced channel edge having enhanced edge characteristics is described in this article.
Abstract: An apparatus, method, and process that includes a substantially transparent substrate having a first surface, a second surface, and edge extending around at least a portion of a perimeter of the substantially transparent substrate, wherein the edge being a laser induced channel edge having enhanced edge characteristics.

38 citations

Journal ArticleDOI
TL;DR: In this article, the authors used 800 nm femtosecond laser pulses to carry out the drilling while monitoring the plasma emission with a spectrometer system and reported detection of a metal layer buried deep inside silicon by creating an access hole through the semiconductor.
Abstract: Femtosecond laser micromachining together with Laser Induced Breakdown Spectroscopy (LIBS) allows us to drill precise hole in materials to internal buried layers as well as characterize the materials while drilling. We report detection of a metal layer buried deep inside silicon by creating an access hole through the semiconductor. We used 800 nm femtosecond laser pulses to carry out the drilling while monitoring the plasma emission with a spectrometer system. Higher drilling rates of 1 μm per shot were achieved using a Gaussian laser beam profile with peak fluences of 42 J/cm2. Lower drilling rates of 30 nm per pulse with better accuracy could be achieved using lower intensity flat top beam profiles at fluences of 1.4 J/cm2.

14 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a new proof of the general interference law for partially coherent fields is obtained and is illustrated by simple and direct experiments, which show the changes in the visibility of the fringes as the degree of coherence varied and the results are compared with the predictions of the theory.
Abstract: Two-beam interference with partially coherent light is discussed. A new proof of the general interference law for partially coherent fields is obtained and is illustrated by means of simple and direct experiments. Photographs are given which show the changes in the visibility of the fringes as the degree of coherence varied and the results are compared with the predictions of the theory.

201 citations


"Optical coherence and beamspread in..." refers methods in this paper

  • ...Young’s two-slit apparatus Transverse coherence is typically measured using Young’s two slit apparatus.(10) This method measures the coherence of one part of the image against another by interfering portions of the beam with each other....

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Journal ArticleDOI
TL;DR: In this article, it was shown that certain partially coherent model sources whose intensity distribution and degree of coherence are both gaussian will generate the same far-field intensity distributions as a completely coherent laser source.

192 citations


"Optical coherence and beamspread in..." refers background in this paper

  • ...A planar and secondary source generating Gaussian Schell-model beams is a beam which displays Gaussian distributions of both the optical intensity and the degree of transverse coherence.(11,12) The degree of spatial coherence measures the correlations between the amplitudes of the optical field at two points across the beam and it is the normalized form of the transverse spatial coherence function, more precisely the cross-spectral density function....

    [...]

Journal ArticleDOI
TL;DR: A fiberless 1-TW all-Nd:glass chirped-pulse-amplification laser system that uses high-contrast 0.8-1.4-ps pulses produced directly from a Nd: glass feedback-controlled oscillator, thereby minimizing gain-bandwidth narrowing and offering improved contrast with amplified stimulated emission background.
Abstract: We have developed a fiberless 1-TW all-Nd:glass chirped-pulse-amplification laser system that uses high-contrast 0.8–1.4-ps pulses produced directly from a Nd:glass feedback-controlled oscillator. Employing grating-only expansion and compression, the system produces clean (~107 contrast ratio) 1-J, 1–1.4-ps recompressed pulses without added pulse cleaning. Clean microjoule-energy pulses from the oscillator require less subsequent amplification than cw oscillator schemes, thereby minimizing gain–bandwidth narrowing and offering improved contrast with amplified stimulated emission background.

32 citations

Book
10 Feb 2006
TL;DR: In this paper, three laser technologies in which TRUMPF participated will be investigated from conception to realization, focusing on the diffusion cooled coaxial CO2 laser geometry with diffraction limited resonators.
Abstract: It is astonishing how long it can take from the first idea to the industrial success of a laser technology product. Three laser technologies in which TRUMPF participated will be investigated from conception to realization. The first case study focuses on the diffusion cooled coaxial CO2 laser geometry with diffraction limited resonators. The second case study highlights some of the stages along the very successful route to implementation of the thin disk laser; from the conception at the IFSW and the ITP, both in Stuttgart, to the successful industrial installations in automotive applications. Finally the development of high power diodes for diode pumped solid state lasers is also discussed.

17 citations

Journal ArticleDOI
TL;DR: A reciprocity inequality is derived, involving the effective size of a planar, secondary, Gaussian Schell-model source and the effective angular spread of the beam that the source generates, to imply that a fully spatially coherent source of that class has certain minimal properties.
Abstract: A reciprocity inequality is derived, involving the effective size of a planar, secondary, Gaussian Schell-model source and the effective angular spread of the beam that the source generates. The analysis is shown to imply that a fully spatially coherent source of that class (which generates the lowest-order Hermite-Gaussian laser mode) has certain minimal properties.

11 citations


"Optical coherence and beamspread in..." refers background in this paper

  • ...A planar and secondary source generating Gaussian Schell-model beams is a beam which displays Gaussian distributions of both the optical intensity and the degree of transverse coherence.(11,12) The degree of spatial coherence measures the correlations between the amplitudes of the optical field at two points across the beam and it is the normalized form of the transverse spatial coherence function, more precisely the cross-spectral density function....

    [...]