Double EF – Elongated Focus Element

Double EF is a unique binary diffractive element that doubles the Depth of Focus (DOF) relative to a single mode Gaussian beam. Double EF have the advantage of suppressed side lobes known for Bessel-like beams. For certain applications (microscopy, micro-material processing) it can be of vital importance.

This passive elongated focus element can replace the need for a complex dynamic opto-mechanical device or be used to distribute laser energy more efficiently in the depth for material processing.

Due to the subtle effect, the phenomena of the elongated focus is noticed only when using a single mode laser with an M2 < 1.3. For Multimode laser sources, the DOF extension will be negligible. For a larger focus elongation, we suggest multi-level solutions which can be found here: https://www.holoor.co.il/product/multifocal/.

In the simulation result in Figure 1, we compare the profile of a single mode laser TEM00 with and without using an EF element. DOF defined at FWHM along Z-axis is about four times the Rayleigh length or twice larger than the DOF of a Gaussian beam.

Figure 2presents the suppressed side lobes. One can notice that in most of the DOF region, the side lobes are below 3% relative to the peak intensity.

binary elongated focus simulation extended depth of focus
Figure 2. Sidelobes analysis of the Double EF element depicted as height levels.
Figure 2. Sidelobes analysis of the Double EF element depicted as height levels.