Bessel beams from an Nd:YAG laser via an immersed acute-apex axicon

Over the past several decades Bessel beams have attracted much attention and found many applications thanks to their non-diffraction characteristics and other features. One of the common solutions to obtain a zero-order Bessel-like laser beam is the illumination of an axicon by a Gaussian beam which forms a beam with the sharp peak encircled by rings. Most of the work on Bessel beams has been done using obtuse-apex axicons in air. Immersed axicons allow one to tune Bessel beam parameters: conical angle θ , peak radius w , focal length Z f by changing the composition or temperature of the liquid in the cuvette with an axicon. We present preliminary experiments and calculations to show that immersion also opens the possibility to form Bessel beams by “non-conventional” acute-angled axicons, which do not work in air due to the total internal reflection at the conical surface. The calculated θ , w , Z f parameters of Bessel beams formed by axicons immersed in liquids with refractive indices from n liq ≈ 1.33 (water) to n liq ≈ 1.45 , immersion for quartz (fused silica), and by axicons in air are compared. This comparison shows that using immersed acute-angled axicons it is possible to obtain Bessel beams with parameters at the level of axicons operating in air. For the first time, Bessel-like laser beams were obtained using an acute-apex (78 ∘ ) quartz axicon in a cuvette with various liquids at the output of an Nd:YAG laser in a quasi-continuous regime. Immersion of the axicon helped to correct beam distortions caused by apex damage generated during axicon manufacturing. Tuning of beams’ peak radii from w < 10 μ m to w ≈ 300 μ m with changes in the liquid mixture composition and temperature is demonstrated. The features of the obtained Bessel-like beams, schemes to avoid problems associated with the axicons’ apex and possible applications of immersed axicons are discussed.