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8The 30th International Conference on Advanced Laser Technologies
ALT'23
LS-I-3
Towards the gas-discharge fiber lasers
I.A. Bufetov, A.V. Gladyshev, A.P. Mineev, S.M. Nefedov, V.V. Velmiskin
Prokhorov General Physics Institute of the Russian Academy of Sciences, 38 Vavilov St., Moscow, Russia
The advent of low-loss hollow-core optical fibers (HCFs) enabled the development of a new type of lasersgas fiber lasers (GFLs). To date, various GFLs have already been demonstrated. An active medium of such lasers is some Raman-active or dipole-active gas that fills the hollow-core of a fiber. To excite the active medium, the GFLs rely on optical pumping by some solid-state laser. To fully realize the possibilities of hollow fibers (resistance to high-intensity radiation, wide spectral transmission range, etc.) in all-fiber optical schemes, it is necessary to solve the problem of generating laser radiation directly in HCF. Using an electric discharge to excite the active medium of a GFL can solve this problem. However, at small core diameters (Dc~100 ^.m) of HCFs the researchers encountered the instability of the electric discharge.
To excite plasma in the core of a hollow fiber, a scheme like a slot antenna in the wall of a metal microwave waveguide was proposed by us and implemented [1]. Using the proposed scheme, the possibility of maintaining noble gases plasma in the core of a hollow fiber with a diameter as small as 100 ^m was demonstrated (Fig.1). The total length of plasma column in the hollow-core fiber was up to 25 cm. The frequency of microwave radiation used was 2.4 GHz, the average generated power was below 20 W. The results obtained show that the microwave slot antenna is a promising pumping scheme for gas-discharge fiber lasers based on hollow-core fibers.
The minimum values of the electric microwave field (v = 2.45 GHz), which are necessary to maintain discharge in several noble gases (Ar, Ne (see Fig.2), and He) in optical fibers with hollow cores of small diameter up to 100 ^m, have been measured for the first time [2]. The minimal electric field intensity values for all three gases are (2.5-2.8) kV/cm at a pressure of argon p~50 Torr, neon p~300 Torr, and helium p~500 Torr.
Fig.1. Picture of MW discharge in HCF (DC=110 ^m, Ne, p=30 Torr) placed in the slot of MW guide wall. a) general view; b) improved
200 300
Pressure, torr
Fig.2. Threshold values of the electric field required to maintain
(EM) the discharge in Ne and for electrical breakdown (EB) by the
MW depending on the pressure. Lines 1 -3 (refer to the left and
. ■ „,. tt^t, ■ . . . . . n, , ■. bottom axes): dependences EUp) for neon-filled HCFs for different spatial resolution. The HCF is located on the lower edge of the slot with „ T- . _ , ■ . V . n ^
■ f, , . DC. Lines 4-5 (refer to the right and upper axes): the EB(p)
a width of d 1.5 mm. iij? - -m^ii i ... ■ .<.■
dependences for neon given in [3] for much larger characteristic
dimension of the discharge volume D.
The implementation of a stable MW discharge in a HCF filled with noble gases is a significant advance towards solving the problem of creating fiber gas lasers based on hollow-core fibers.
This research was supported by Russian Science Foundation (grant No. 22-19-00542), https://rscf.ru/pro-ject/22-19-00542/.
[1] A. Gladyshev, S. Nefedov, A. Kolyadin et al. Microwave Discharge in Hollow Optical Fibers as a Pump for Gas Fiber Lasers, Photonics, vol.9, p.752 (2022).
[2] I. Bufetov, A. Gladyshev, S. Nefedov et al. MW discharge maintaining in the hollow core fibers for gas fiber lasers, Doklady RAS Physics, vol.509, pp. 3-8, (2023) (in Russian).
[3] A.D. MacDonald, Microwave Breakdown in Gases (JohnWiley & Sons, Ink.: New York) Chapters 1, 5 (1966).
