Investigation of diffractive optical element femtosecond laser machining

•A method for rapid manufacturing of optical diffractive element in BK7 is proposed.•A binary grating in BK7 was successfully machined by femtosecond laser pulses.•Process relying on nonlinear absorption in the dielectric due to photoionization.•The binary grating was analysed by SEM and interferome...

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Bibliographic Details
Published in:Applied surface science 2016-06, Vol.374, p.375-378
Main Authors: Chabrol, Grégoire R., Ciceron, Adline, Twardowski, Patrice, Pfeiffer, Pierre, Flury, Manuel, Mermet, Frédéric, Lecler, Sylvain
Format: Article
Language:English
Subjects:
Dielectric materials
Diffractive optical elements
Engineering Sciences
Femtosecond
Gratings (spectra)
Grooves
Laser machining
Laser processing
Lasers
Optical diffractive elements
Other
Scanning electron microscopy
Ultra-short pulse laser
White light interferometry
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Summary:•A method for rapid manufacturing of optical diffractive element in BK7 is proposed.•A binary grating in BK7 was successfully machined by femtosecond laser pulses.•Process relying on nonlinear absorption in the dielectric due to photoionization.•The binary grating was analysed by SEM and interferometric microscopy.•Simulations by Fourier modal method supported the measured diffractive efficiency. This paper presents an explorative study on the machining of diffractive optical elements (DOEs) in transparent materials using a femtosecond laser source. A simple form of DOE, a binary phase grating with a period of 20.85μm (σ=0.5μm), a groove depth and width of 0.7μm (σ=0.2μm) and 8.8μm (σ=0.5μm) respectively, was successfully machined in BK7. The topographic characteristics were measured by white light interferometry and scanning electron microscopy (SEM). The processing was carried out on high precision stages with an ultrafast fibre laser (350fs) emitting a 343nm pulse focused onto the sample with a stationary microscope objective. A diffracted efficiency of 27%, obtained with a spectro goniometer, was corroborated by the theoretical results obtained by the Fourier modal method (FMM), taking into account the measured topographic values. These encouraging results demonstrate that high-speed femtosecond laser manufacturing of DOE in bulk glasses can be achieved, opening the way to rapid prototyping of multi-layered-DOEs.
ISSN:0169-4332
1873-5584
DOI:10.1016/j.apsusc.2016.01.079