Chemically assisted femtosecond laser machining for applications in LiNbO3 and LiTaO3

We introduce and optimize a fabrication procedure that employs both femtosecond laser machining and hydrofluoric acid etching for cutting holes or voids in slabs of lithium niobate and lithium tantalate. The fabricated structures have 3 μm lateral resolution, a lateral extent of at least several millimeters, and cut depths of up to 100 μm. Excellent surface quality is achieved by initially protecting the optical surface with a sacrificial silicon dioxide layer that is later removed during chemical etching. To optimize cut quality and machining speed, we explored various laser-machining parameters, including laser polarization, repetition rate, pulse duration, pulse energy, exposure time, and focusing, as well as scanning, protective coating, and etching procedures. The resulting structures significantly broaden the capabilities of terahertz polaritonics, in which lithium niobate and lithium tantalate are used for terahertz wave generation, imaging, and control. The approach should be applicable to a wide range of materials that are difficult to process by conventional methods.

[1]  Martin C. Nuss,et al.  Electrooptical generation and detection of femtosecond electrical transients , 1988 .

[2]  T. Feurer,et al.  Spatiotemporal Coherent Control of Lattice Vibrational Waves , 2003, Science.

[3]  Time-resolved coherent imaging of a THz multilayer response , 2009 .

[4]  Alexander A. Serafetinides,et al.  Picosecond and subpicosecond visible laser ablation of optically transparent polymers , 1998 .

[5]  R. Kremer,et al.  Micro structuring of LiNbO3 by using nanosecond pulsed laser ablation , 2007 .

[6]  K. Nelson,et al.  Direct visualization of terahertz electromagnetic waves in classic experimental geometries , 2012 .

[7]  Gerard Mourou,et al.  Machining of sub-micron holes using a femtosecond laser at 800 nm , 1995 .

[8]  Bernard Fay,et al.  Advanced optical lithography development, from UV to EUV , 2002 .

[9]  Qiang Wu,et al.  Quantitative phase contrast imaging of THz electric fields in a dielectric waveguide. , 2009, Optics express.

[10]  K. Nelson,et al.  High-Resolution, Low-Noise Imaging in THz Polaritonics , 2013, IEEE Transactions on Terahertz Science and Technology.

[11]  M. Späth,et al.  Time resolved dynamics of subpicosecond laser ablation. , 1993 .

[12]  E.L. Wooten,et al.  A review of lithium niobate modulators for fiber-optic communications systems , 2000, IEEE Journal of Selected Topics in Quantum Electronics.

[13]  K. Nelson,et al.  Terahertz reflection response measurement using a phonon polariton wave , 2009 .

[14]  K. Nelson,et al.  Fabrication of polaritonic structures in LiNbO3 and LiTaO3 using femtosecond laser machining , 2006 .

[15]  K. Rajurkar,et al.  Investigation of Femtosecond Laser-assisted Micromachining of Lithium Niobate , 2004 .

[16]  Keith A. Nelson,et al.  Direct Visualization of Collective Wavepacket Dynamics , 1999 .

[17]  K. Nelson,et al.  Time-resolved imaging of near-fields in THz antennas and direct quantitative measurement of field enhancements. , 2012, Optics express.

[18]  M. Müllenborn,et al.  Sub‐band‐gap laser micromachining of lithium niobate , 1995 .

[19]  A Ostendorf,et al.  Sub-diffraction limited structuring of solid targets with femtosecond laser pulses. , 2000, Optics express.

[20]  G. Mourou,et al.  Laser ablation and micromachining with ultrashort laser pulses , 1997 .

[21]  E. Mazur,et al.  Femtosecond laser micromachining in transparent materials , 2008 .

[22]  K. Nelson,et al.  Integrated diffractive terahertz elements , 2003 .

[23]  R. Haglund,et al.  Ultraviolet‐laser‐induced desorption of atoms, ions, and molecules from lithium niobate , 1994 .

[24]  Fumiyo Yoshino,et al.  Heat accumulation effects in femtosecond laser-written waveguides with variable repetition rate. , 2005, Optics express.

[25]  Keith A. Nelson,et al.  Impulsive stimulated Raman scattering experiments in the polariton regime , 1992 .

[27]  Thomas Feurer,et al.  Terahertz polariton propagation in patterned materials , 2002, Nature materials.

[28]  Microstructuring of lithium niobate single crystals using pulsed UV laser modification of etching characteristics , 2002 .

[29]  Qiang Wu,et al.  Experimental and theoretical analysis of THz-frequency, direction-dependent, phonon polariton modes in a subwavelength, anisotropic slab waveguide. , 2010, Optics express.

[30]  Michael J. Hoffmann,et al.  Generation of high-power terahertz pulses by tilted-pulse-front excitation and their application possibilities , 2008 .

[31]  K. Nelson,et al.  Generation of multicycle terahertz phonon-polariton waves in a planar waveguide by tilted optical pulse fronts , 2009 .

[32]  T. Feurer,et al.  Imaging of THz waves in 2D photonic crystal structures embedded in a slab waveguide , 2010 .

[33]  A. Ostendorf,et al.  Towards nanostructuring with femtosecond laser pulses , 2003 .

[34]  M. Stuke,et al.  Sub-picosecond UV laser ablation of metals , 1995 .

[35]  Gary Cook,et al.  Microstructuring of lithium niobate using differential etch-rate between inverted and non-inverted ferroelectric domains , 1998 .

[36]  E. Mazur,et al.  Bulk heating of transparent materials using a high-repetition-rate femtosecond laser , 2003 .

[37]  T. Gaylord,et al.  Lithium niobate: Summary of physical properties and crystal structure , 1985 .

[38]  K. Nelson,et al.  Analysis of phase contrast imaging of terahertz phonon-polaritons , 2008 .

[39]  Luis Arizmendi,et al.  Photonic applications of lithium niobate crystals , 2004 .

[40]  Qiang Wu,et al.  Comparison of phase-sensitive imaging techniques for studying terahertz waves in structured LiNbO_3 , 2010 .

[41]  Inspec,et al.  Properties of lithium niobate , 1989 .

[42]  Fredrik Laurell,et al.  Wet etching of proton-exchanged lithium niobate—a novel processing technique , 1991 .

[43]  J G Fujimoto,et al.  Three-dimensional photonic devices fabricated in glass by use of a femtosecond laser oscillator. , 2005, Optics letters.

[44]  K. Nelson,et al.  Generation of 10 μJ ultrashort terahertz pulses by optical rectification , 2007 .

[45]  K. R. Williams,et al.  Etch rates for micromachining processing , 1996 .

[46]  Martin Richardson,et al.  Practical uses of femtosecond laser micro-materials processing , 2003 .

[47]  Alan Arai,et al.  Waveguide writing in fused silica with a femtosecond fiber laser at 522 nm and 1 MHz repetition rate. , 2005, Optics express.

[48]  Wolfgang Schulz,et al.  Laser machining by short and ultrashort pulses, state of the art , 2002 .