Optical trapping with superfocused high-M²laser diode beam

Abstract

Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M 2 values in double-digits. We propose a method of 'interference' superfocusing of high-M 2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with highprecision direct laser writing. Using axicons with apex angle 140 0 and rounded tip area as small as ~10 μm diameter, we demonstrate 2-4 μm diameter focused laser 'needle' beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M 2 =18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of ~11 μm that could be achieved if focused by an 'ideal' lens of unity numerical aperture. The same technique using a 160 0 axicon allowed us to demonstrate few-μm-wide laser 'needle' beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations.

Holographic Image Denoising using Random Laser Illumination

“…This article demonstrates the M 2 measurement of perovskite and perovskite–polystyrene 10 wt%‐based random lasers using a commercial (Gentec, Beamage–M2) automated beam quality factor measurement system. [ 63–65 ] The random lasers light was collected by a 100x objective lens followed by a focusing lens to the Beamage–M2 measurement system. Figure 6 a,b shows the measured and the hyperbolic fit of beam diameter as a function of the position that is the beam propagation in the Z ‐direction.…”

Sensing resonating devices fabricated on optical fibers using multi-photon polymerization technique

“…More specifically, photonic elements including micro-prisms, woodpile and chiral photonic crystals [121][122][123], micro-lenses (spherical, cylindrical, conical, toric lenses) [121,[123][124][125][126], parabolic micro-reflectors [127], spherical surface-enhanced Raman scattering (SERS) radar configurations [128], phase masks [129], axicons [130][131][132], gradient index anti-reflective coatings [133] and polarization filtering [123], have been fabricated on the endface of optical fibers in recent years by several groups.…”

“…The fabricated elements are being used in a variety of applications such as beam shaping or focusing [123,126], SERS sensors [128], or even in bio-imaging [124] and biomedical applications [132].…”