Abstract

We present novel results obtained in the fabrication of high-aspect ratio micro-fluidic microstructures chemically etched from fused silica substrates locally exposed to femtosecond laser radiation. A volume sampling method to generate three-dimensional patterns is proposed and a systematic SEM-based analysis of the microstructure is presented. The results obtained gives new insights toward a better understanding of the femtosecond laser interaction with fused silica glass (a-SiO2).

© 2004 Optical Society of America

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References

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Appl. Opt.

Appl. Phys. A - Mater

C. Schaffer, J. Garcia and E. Mazur �??Bulk heating of transparent materials using a high repetition-rate femtosecond laser,�?? Appl. Phys. A - Mater 76, 351-354 (2003).
[CrossRef]

J. Appl. Physics

K. Awazu, H. Kawazoe, �??Strained Si �?? O �?? Si bonds in amorphous SiO2 materials: A family member of active centers in radio, photo, and chemical responses,�?? J. Appl. Physics 94, 6243-6262 (2003).
[CrossRef]

J. Non-Cryst. Solids

A. Agarwal and M. Tomozawa, �??Correlation of silica glass properties with the infrared spectra,�?? J. Non-Cryst. Solids 209, 166-174 (1997).
[CrossRef]

J. Opt. Soc. Am. B

Jpn. J. Appl. Phys.

Y. Kondo, T. Suzuki, H. Inouye, K. Miura, T. Mitsuyu, and K. Hirao, �??Three-Dimensional Microscopic Crystallization in Photosensitive Glass by Femtosecond Laser Pulses at Nonresonant Wavelength,�?? Jpn. J. Appl. Phys. 37, L94 - L96 (1998).
[CrossRef]

MRS Proceedings

Y. Bellouard, A. Said, M. Dugan, P. Bado, �??Monolithic Three-Dimensional Integration of Micro-Fluidic Channels and Optical Waveguides in Fused Silica,�?? MRS Proceedings, vol. 782, Boston 2003 (in press).
[CrossRef]

NFOEC

P. Bado, A. Said, M. Dugan, T. Sosnowski, and S. Wright, �??Dramatic improvements in waveguide manufacturing with femtosecond lasers,�?? in NFOEC, Dallas, Sept. 2002.

Opt. Express

Opt. Lett.

Photonics West, Proc. SPIE

R. Gattass, I. Maxwell, J. Ashcom, and E. Mazur, �??Transition from repetitive to cumulative thermal processing in femtosecond laser induced machining of embedded waveguides�?? in Photonics West, Proc. SPIE 4978, 43 (2004).

Phys. Rev. B

C. Fiori, R.A.B. Devine, �??Evidence for a wide continuum of polymorphs in a-SiO2,�?? Phys. Rev. B 33, 2972-2974 (1986).
[CrossRef]

Solid State Commun.

F. L. Galeener, �??Planar rings in glass,�?? Solid State Commun. 44, 1037-1040 (1982).
[CrossRef]

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Figures (10)

Fig. 1.
Fig. 1.

Illustration of the volume sampling process: by moving the substrate in the three directions, one can connect laser-affected zones and forms larger patterns (left). Laser-affected zones (LAZ) are represented by an ellipsoid and since fs-laser matter interaction involved nonlinear process, the ellipsoid short axis can be smaller than the spot-size itself. The volume to be etched is sampled by connecting discrete unit-LAZ zones. Right: a typical refractive index map obtained after femtosecond laser exposure of a single line. This pattern was taken as a reference to define the shape and size of a unit-LAZ. The map was obtained using a refractive near-field profilometer.

Fig. 2.
Fig. 2.

Micro-tunnel: optical and scanning electron microscopes observations [7]. The width (in μm), measured along the tunnel length, is indicated in italic on the schematic diagram of the tunnel.

Fig. 3.
Fig. 3.

SEM and optical pictures of the front end of a partially etched tunnel. The tunnel is 0.8 mm long and about 70 μm wide at the largest cross-section. Two different etching regimes (A and B) are clearly visible.

Fig. 4.
Fig. 4.

Surface channel. Left - Time dependant depth etching rate. For this measurement, a micro-channel made of 15 × 90 parallel lines (30 μm wide, 675 μm deep).

Fig. 5.
Fig. 5.

Single-track channels profile. These channels were obtained by stacking lines only in the z-direction.

Fig. 6.
Fig. 6.

Micro-channels (after 135 min): view from the glass edge (left) and further away (right).

Fig. 7.
Fig. 7.

Partially etched channels: three different level of power were used: from left to right: 55 (top view), 540, 1075 nJ. Number of lines is identical for the three channels.

Fig. 8.
Fig. 8.

(left): Surface structure of etched channels at six different level of energy. The two pictures shown on the right shows a top view of two channels. All channels were made in the same piece and with the same number of unit-LAZs.

Fig. 9.
Fig. 9.

A microchannel partially etched after one hour etching time. The picture on the right is a magnification of the channel central region. Distance between laser-exposed regions is 500 nm.

Fig. 10.
Fig. 10.

Partially etched channel: distance between lines was 2 μm. The channel goes 675 μm deep. The left picture shows an overview of the partially etched channel after two hours etching time. The right picture is a magnification of the boundary between etched and un-etched zones.

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