A 1.9μm Tm: YLF external cavity mode conversion vortex laser based on LD off-axis pump

doi:10.1016/j.optcom.2020.126596

Optics Communications

Volume 482, 1 March 2021, 126596

https://doi.org/10.1016/j.optcom.2020.126596 Get rights and content

Highlights

•
A 1. $9 μ m$ Tm:YLF high-order vortex laser output is realized for the first time.
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The continuous tuning and chirality control of topological charge are realized.
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A high stability LG_1,0 mode laser with the maximum power of 8.5 W is achieved.

Abstract

In this work, a 1. $9 μ m$ Tm:YLF high-order vortex laser output is realized for the first time based on LD off-axis pumping technology. By adjusting the off-axis displacement of the output coupling mirror accurately, the maximum topological charge up to $m = 20$ for stable Hermite–Gaussian (HG $_{m,0}$ ) mode is achieved. The conversion of high-order HG $_{m,0}$ to Laguerre–Gauss (LG $_{m,0}$ ) modes are further realized by a $π$ /2 mode converter, and the topological charge and chirality of LG $_{m,0}$ modes are measured by the Mach–Zehnder (MZ) interferometer system. The maximum output power of the LG $_{1,0}$ mode vortex laser was measured to be 8.5W with the central wavelength of 1908.8 nm. The wavelength and the power instability are less than 0.72 nm and better than $\pm$ 5.9%, respectively. This work proves that the 1. $9 μ m$ Tm:YLF laser has the potential to achieve continuous tuning and easy chirality control for the high-order vortex optical mode output, and lays a foundation for high-power mid-infrared vortex laser applications.

Introduction

The vortex beam carrying orbital angular momentum (OAM) plays critical role in fields such as multiplexing optical communication [1], quantum entanglement [2], new optical tweezers [3], and metamaterials micro–nano machining [4], because of its unique properties such as singular transverse mode shape, vortex wavefront and phase singularity. The mid-infrared $2 μ m$ band laser finds important applications in advanced medical treatment [5], environmental monitoring [6], and mid-and-far infrared nonlinear optical frequency conversion technology [7]. If the original technology of $2 μ m$ laser is used to further study the vortex beam carrying OAM, it will surely stimulate further innovation of the vortex beam and $2 μ m$ laser technology. Currently the common technical means to realize vortex laser output mainly include the liquid crystal q-wave-plate, spatial light modulator and spiral phase plate [8], [9], [10]. However, the optical mode conversion devices used in these methods are usually expensive and complicated to manufacture. In contrast, the use of a $π$ /2 mode converter composed of two cylindrical lenses can directly convert the high-order HG mode into a high-order HG mode carrying OAM, which is cost saving and easy to implement. Previous report showed that $1 μ m$ wavelength tunable vortex laser output was achieved by this method [11], and the highest topological charge of the HG mode reached m $=$ 15, and most of the reported solid-state vortex laser output is concentrated near the $1 μ m$ band. There was also report showing that $2 μ m$ Ho:YAG three-lobe and five-lobe vortex laser was achieved with phase plate modulation seed light injection technology [12]. However, because it uses a fixed-order phase plate, a continuous tuning of the topological charge cannot be achieved. As far as we know, there are no reports about the solid vortex laser output generated at 1. $9 μ m$ band by mode converter.

In this paper, based on LD off-axis pumping technology, we achieve a1. $9 μ m$ high-order HG mode laser output using the Tm:YLF crystal for the first time, and then converting the high-order HG mode beam to high-order LG mode vortex laser output with a $π$ /2 mode converter. The topological charge and chirality of LG mode were measured by MZ interference system. The wavelength and the power instability of the LG $_{1,0}$ mode vortex laser are measured. Our results show that the 1. $9 μ m$ Tm:YLF laser has the potential to achieve high-order vortex mode output.

Section snippets

Experimental setup

The experimental setup of LD off-axis pumping 1. $9 μ m$ Tm:YLF laser system is shown in Fig. 1. A high-power 792 nm fiber-coupled laser diode was used as the pump source, with the fiber core diameter of $200 μ m$ and the numerical aperture of NA $=$ 0.22. The pump light was focused to the center of the crystal through two 792 nm anti-reflective (AR) coated lenses which the focal length ratio of F1:F2 $=$ 35:75 mm. The beam waist radius of $210 μ m$ was finally focused on the crystal. The Tm:YLF crystal size

Experimental results and analysis

First, the HG $_{m,0}$ mode generated by the LD off-axis pumping Tm:YLF laser was measured, as shown in Fig. 3. When the cavity was strictly coaxial, the threshold of HG $_{0,0}$ mode (TEM₀₀, m $=$ 0) output was 6.1 W. As the off-axis displacement of the OC mirror increases, the TEM₀₀ mode splits in transverse, and the topological charge of the original HG $_{0,0}$ mode gradually increases to the higher-order HG $_{m,0}$ mode. When the off-axis displacement was tuned from $245 μ m$ to $1390 μ m$ . the topological charge form m $=$

Conclusions

In summary, a 1. $9 μ m$ Tm:YLF high-order vortex laser output has been achieved for the first time by using LD off-axis pumping Tm:YLF cavity mode conversion vortex laser system. By precisely adjusting the off-axis displacement of the OC mirror, the maximum topological charge reaches m $=$ 20 for stable HG $_{20,0}$ mode has been achieved. Furthermore, the vortex laser output is realized by using a $π$ /2 mode converter to convert the high order HG $_{m,0}$ to LG $_{m,0}$ mode. The output power of the high-power LG $_{1,0}$

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This work was supported by the Science and Technology Department Project of Jilin Province Grant (No. 20200246JC).

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Study on the effect of pump beam on the purity of high-order HG mode in off-axis pumped Tm:YLF laser
2023, Infrared Physics and Technology
In this paper, the effect of the pump beam radius on the purity of the HG modes is investigated based on the off-axis pumped Tm:YLF laser, and LG mode vortex laser of 1.9 μm is realized. The multi-mode rate equations are established to reveal that a smaller pump beam radius leads to higher purity of the HG mode beam. At the same time, it is experimentally found that each HG mode alternated with increasing off-axis displacement at a pump beam radius of 200 μm, with a purity of 87.9 % for the HG_8,0 mode. However, at the pump beam is 400 μm, the phenomenon of multiple HG modes output increases in the process of adjusting the off-axis displacement. The consistency between the experimental and theoretical results proves the effect of the size of the pump beam on the purity of the high-order HG mode laser. The 1.9 μm LG vortex beam within the 8th order is achieved with a pump beam radius of 200 μm, and the slope efficiency of the LG_1,0 mode could reach 34.51 %.
Study on 1.9 μm structured lasers based on Ince–Gaussian modes superposition with multi-modulation by different directions off-axis dual-end-pump
2023, Optics Communications
The double $I G_{p, p}^{e}$ modes multi-modulation superposition evolution structured lasers output is realized, based on the proposed different directions off-axis dual-end-pumping Tm:YLF laser method. Under the modes orthogonal superposition, the theoretical simulation and experimental measurement results have a high degree of agreement, and the orthogonal superposition of double $I G_{p, p}^{e}$ modes within 5 orders is realized, which proves that different order modes and optical field intensity ratio have the capability to modulate the formation of vortex array structured beams. When the low-order $I G_{p, p}^{e}$ modes of the same order are orthogonally superimposed, the phenomenon of superposition of different phase differences occurs, which proves the possibility of modulating the superposition of $I G_{p, p}^{e}$ modes by the phase difference. At the same time, it is found that the regular pattern output of high-order $I G_{p, m}$ modes (odd mode m $\leq$ 3 or even mode m $\leq$ 2) can be realized at different angles, which proves the ability of rotation angle to modulate the superposition of double $I G_{p, p}^{e}$ modes. Finally, the $1.9 μ m$ Tm:YLF structure laser output with double $I G_{p, p}^{e}$ modes multi-factor composite modulation superposition evolution within 10 orders is realized. When the 10-order double $I G_{10, 10}^{e}$ modes are superimposed, the output power exceeds 5.7 W, and the conversion efficiency is higher than 17.5%.
Off-axis pumped Tm:YLF vortex laser with continuously tunable wavelength
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Citation Excerpt :
At present, most of the research on the tuning of vortex beam is concentrated near the 1 μm band. In the 2 μm band, Liu Jingliang realized the tuning of the orbital angular momentum of the 1.9 μm vortex beam based on off-axis pumping Tm:YLF [17]. There is no report about the 2 μm wavelength tunable vortex laser.
In this paper, HG mode conversion and etalon are used to achieve a 1.9 μm vortex beam output in a Tm:YLF laser while achieving a certain range of wavelength continuous tuning. In theory, the wavelength tuning characteristic and tuning capability of the etalon are analyzed. In the experiment, the HG_1,0 mode laser is achieved by off-axis pump, and the optical field distribution and beam quality are relatively consistent with the theoretical state. After the HG_1,0 mode laser passes through the π/2 mode converter, the LG_1,0 vortex beam output is realized. The optical field distribution and beam quality of the vortex beam are relatively close to the theoretical state. The threshold of the laser at LG_1,0 mode is 3.2 W, the slope efficiency is 37.7%, the optical–optical conversion efficiency is 34%, and a laser output of 8.6 W is obtained at the highest pump power of 25.3 W. On this basis, the continuous wavelength tuning of the LG_1,0 mode vortex beam from 1937 nm to 1921 nm was achieved by rotating the etalon. Through comparison, it can be found that the optical field distribution and output power of each wavelength are relatively close during the wavelength tuning process. Finally, the topological charge of the vortex beam is measured by the interference of the vortex beam with the spherical wave and the plane wave. This article is of great significance for the further research of multi-dimensional tuning to realize large-capacity optical communication.
Study on the Generation of 1.9 μm Mode Superposition Conversion Laser by Double-End Off-Axis Pumping
2024, Photonics
Customized Micron-Scale Waveguide-Grating Structure for Vortex Laser Emission in Tm:YLF Processed by Femtosecond Laser Direct Writing
2023, Journal of Lightwave Technology
An Orbital-Angular-Momentum- and Wavelength-Tunable 2 μm Vortex Laser
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View full text

A 1.9μm Tm: YLF external cavity mode conversion vortex laser based on LD off-axis pump

Highlights

Abstract

Introduction

Section snippets

Experimental setup

Experimental results and analysis

Conclusions

Declaration of Competing Interest

Acknowledgment

Opt. Lett.

Opt. Commun.

Advances in communications using optical vortices

Photonics Res.

Twisted photons: New quantum perspectives in high dimensions

Light Sci. Appl.

Advanced optical trapping by complex beam shaping

Laser Photonics Rev.

Direct laser printing of chiral plasmonic nanojets by vortex beams

Opt. Express

A 1. $9 μ m$ Tm: YLF external cavity mode conversion vortex laser based on LD off-axis pump