TY - JOUR

T1 - Raman Lasing and Transverse Mode Selection in a Multimode Graded-Index Fiber with a Thin-Film Mirror on Its End Face

AU - Kuznetsov, Alexey G.

AU - Terentyev, Vadim S.

AU - Simonov, Victor A.

AU - Rizk, Hiba A.

AU - Nemov, Ilya N.

AU - Bronnikov, Kirill A.

AU - Dostovalov, Alexander V.

AU - Babin, Sergey A.

N1 - This research was funded by Russian Science Foundation, grant number 21-72-30024.

PY - 2024/7/24

Y1 - 2024/7/24

N2 - Multimode fibers are attractive for high-power lasers if transverse modes are efficiently controlled. Here, a dielectric thin-film mirror (R~20%) is micro-fabricated on the central area of the end face of a 1 km multimode 100/140 µm graded-index fiber and tested as the output mirror of a Raman laser with highly multimode (M2~34) 940 nm diode pumping. In the cavity with highly reflective input FBG, Raman lasing of the Stokes wave at 976 nm starts at the threshold pump power of ~80 W. Mode-selective properties of mirrors with various diameters were tested experimentally and compared with calculations in COMSOL, with the optimum diameter found to be around 12 µm. The measured Raman laser output beam at 976 nm has a quality factor of M2~2 near the threshold, which confirms a rather good selection of the fundamental transverse mode. The power scaling capabilities, together with a more detailed characterization of the output beam’s spatial profile, spectrum, and their stability, are performed. An approximately 35 W output power with an approximately 60% slope efficiency and a narrow spectrum has been demonstrated at the expense of a slight worsening of beam quality to M2~3 without any sign of mirror degradation at the achieved intensity of >30 MW/cm2. Further power scaling of such lasers as well as the application of the proposed technique in high-power fiber lasers are discussed.

AB - Multimode fibers are attractive for high-power lasers if transverse modes are efficiently controlled. Here, a dielectric thin-film mirror (R~20%) is micro-fabricated on the central area of the end face of a 1 km multimode 100/140 µm graded-index fiber and tested as the output mirror of a Raman laser with highly multimode (M2~34) 940 nm diode pumping. In the cavity with highly reflective input FBG, Raman lasing of the Stokes wave at 976 nm starts at the threshold pump power of ~80 W. Mode-selective properties of mirrors with various diameters were tested experimentally and compared with calculations in COMSOL, with the optimum diameter found to be around 12 µm. The measured Raman laser output beam at 976 nm has a quality factor of M2~2 near the threshold, which confirms a rather good selection of the fundamental transverse mode. The power scaling capabilities, together with a more detailed characterization of the output beam’s spatial profile, spectrum, and their stability, are performed. An approximately 35 W output power with an approximately 60% slope efficiency and a narrow spectrum has been demonstrated at the expense of a slight worsening of beam quality to M2~3 without any sign of mirror degradation at the achieved intensity of >30 MW/cm2. Further power scaling of such lasers as well as the application of the proposed technique in high-power fiber lasers are discussed.

KW - Raman laser

KW - diode pumped

KW - fiber laser

KW - graded-index fiber

KW - mode selection

KW - multimode

KW - thin-film mirror

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85202348085&origin=inward&txGid=514ef49dc1764bdcc1a15a2669d110b1

UR - https://www.mendeley.com/catalogue/f2b52d5b-4c7e-3fe7-b4d0-ba9d35af24fe/

U2 - 10.3390/mi15080940

DO - 10.3390/mi15080940

M3 - Article

C2 - 39203591

VL - 15

JO - Micromachines

JF - Micromachines

SN - 2072-666X

IS - 8

M1 - 940

ER -