Towards all-fiber structure pulsed mid-infrared laser
by gas-filled hollow-core fibers
Wei Huang (黄 威)
1
, Yulong Cui (崔宇龙)
1
, Zhiyue Zhou (周智越)
1
, Zhixian Li (李智贤)
1
,
Yubin Chen (陈育斌)
4
, and Zefeng Wang (王泽锋)
1,2,3,
*
1
College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China
2
State Key Laboratory of Pulsed Power Laser Technology, Changsha 410073, China
3
Hunan Provincial Key Laboratory of High Energy Laser Technology, Changsha 410073, China
4
Luoyang Electronic Equipment Test Center of China, Key Laboratory of Electro-Optical Countermeasures
Test & Evaluation Technology, Luoyang 471003, China
*Corresponding author: zefengwang_nudt@163.com
Received May 6, 2019; accepted June 11, 2019; posted online August 5, 2019
We report here on a diode-pumped pulsed mid-infrared laser source based on gas-filled hollow-core fibers (HCFs)
towards an all-fiber structure by the tapering method. The pump laser is coupled into an acetylene-filled HCF
through a tapered single-mode fiber. By precisely tuning the wavelength of the diode to match different absorp-
tion lines of acetylene near 1.5 μm, mid-infrared emission around 3.1–3.2 μm is generated. With 2 m HCFs and
3 mbar acetylene gas, a maximum average power of 130 mW is obtained with a laser slope efficiency of ∼24%.
This work provides a potential scheme for all-fiber mid-infrared fiber gas lasers.
OCIS codes: 140.3070, 140.3510, 140.4130.
doi: 10.3788/COL201917.091402.
Since the first demonstration of fiber lasers in 1961
[1]
, fiber
lasers have developed rapidly and attracted enormous in-
terests, standing out over other laser sources for the advan-
tages of excellent beam quality, high conversion efficiency,
long interaction length, and long-term stability. Extending
the operation wavelengths of fiber lasers from the near-
infrared to mid-infrared region is an active pursuit because
the retina-safe wavelengths region contains several high
atmospheric transmission windows. It provides a variety
of potential applications in defense, security, atmosphere
monitoring, and medicine
[2]
. Additionally, the mid-infrared
spectral region coincides with rotational–vibrational tran-
sitions of many molecules, and the transition strengths
are generally stronger than corresponding transitions,
which lie in the near-infrared and visible regions, making
mid-infrared sources a natural pump source for longer-
wavelength lasers
[3]
. However, for general silica fibers, the
emission wavelengths are limited below 2.2 μm due to the
maximum phonon energy at room temperature
[2]
.Toobtain
lasers beyond 3 μm, we usually use fibers made of mid-
infrared-transparent soft glasses, such as fluoride glasses
and chalcogenide glasses
[2–6]
. However, due to some inevi-
table restrictions in terms of optical strength, chemical
resistance, thermal stability, and so on, mid-infrared fiber
lasers based on soft glasses are strongly hindered
[2]
.Aswe
all know, gases are common gain media for high power
mid-infrared lasers, especially for wavelengths unavail-
able from rare-earth-doped fibers. The development of
hollow-core fibers (HCFs) with low loss at the mid-infrared
band opened new avenues for mid-infrared fiber lasers by
gases
[7]
.
In the past decade, gas-filled HCFs have been inten-
sively used to generate near-infrared and mid-infrared
laser emissions based on the stimulated Raman scattering
(SRS) effect
[8–14]
and population inversion
[15–20]
. However,
up to now, all these HCF gas lasers are demonstrated
in the structure of spatial light coupling. In the connec-
tion, vacuum chambers or gas cells are usually employed,
and the pump light is launched into HCFs through win-
dows using standard optical components. Although the
coupling efficiency by this approach can be very high, such
a system is bulky and cumbersome. In addition, even tiny
external perturbations can lead to misalignments, decreas-
ing the pump coupling efficiency, and meanwhile increas-
ing the overlap between the incident pump beam and the
HCF’s microstructure, leading to damage at the end of the
HCFs. All these will limit the applications of fiber gas
lasers. A possible alternative coupling method includes
direct fusion splicing of a solid-core single-mode fiber
(SMF) to the HCF
[21]
, which is much more stable and com-
pact compared to the free space coupling arrangement.
Nevertheless, due to the micro-hole collapse effect and
the mode field mismatch between HCFs and SMFs, the
coupling loss will be significantly increased, especially
for anti-resonance HCFs. Recently, a new kind of
technique named a nanospike is reported
[22,23]
, which is fab-
ricated by thermally tapering an SMF down to a diameter
of hundreds of nanometers that can be easily inserted
into the core of the HCF. This way offe rs suppression
of Fresnel reflection and automatic mode-field diameter
matching between the SMF and HCF with very high
launch efficiency.
In this Letter, we demonstrate an all-fiber single-pass
pulsed mid-infrared fiber gas laser based on gas-filled
HCFs by fiber tapering technology. A solid-core SMF,
tapered thermally to a tip with the diameter of several
COL 17(9), 091402(2019) CHINESE OPTICS LETTERS September 2019
1671-7694/2019/091402(4) 091402-1 © 2019 Chinese Optics Letters