Mid-IR HCPCF gas-laser emitting at 4.6 µm

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Mid-IR HCPCF gas-laser emitting at 4.6 µm

Frédéric Gérôme, Farzin Aghbolagh, A. V. Vasudevan Nampoothiri, Benoît Debord, Luca Vincetti, Fetah Benabid, Wolfgang Rudolph

To cite this version:

Frédéric Gérôme, Farzin Aghbolagh, A. V. Vasudevan Nampoothiri, Benoît Debord, Luca Vincetti, et

al.. Mid-IR HCPCF gas-laser emitting at 4.6 µm. Conference on Laser and Electro-Optics /Europe

(CLEO/Europe-EQEC 2019), OSA, Jun 2019, Munich, Germany. Paper CJ-3.4. �hal-02331420�

Mid-IR HCPCF gas-laser emitting at 4.6 µm

Frédéric Gérôme ¹ , Farzin Aghbolagh ² , Vasudevan Nampoothiri ² , Benoit Debord ¹ , Luca Vincetti ³ , Fetah Benabid ¹ , Wolfgang Rudolph ²

1. GPPMM Group, Xlim Research Institute, CNRS UMR 7252, University of Limoges, F-87000 Limoges, France.

2. Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131, USA.

3. Dept. of Engineering "Enzo Ferrari", University of Modena and Reggio Emilia, Italy.

Infrared laser sources emitting in the atmospheric transmission window (i.e. the wavelength range of 3-5 µm and 8-13 µm) are of interest in applications such as remote sensing, imaging and free-space communications [1].

Within this context, Inhibited Coupling Hollow Core Photonic Crystal Fibers (IC-HCPCF) [2] offer an interesting platform for gas laser sources, especially for those emitting in spectral ranges where silica-based solid core fiber lasers fail because of the large infrared (IR) absorption losses of the host materials. Indeed, the possibility of filling HCPCF with gases, and combining long gas-light interaction lengths with small modal areas opened new avenues for laser development and nonlinear optics [3]. Furthermore, IC-HCPCFs exhibit particularly weak optical overlap between the guided field and the glass cladding material (typically in the range 10 ^-4 -10 ^-6 ) [4]. Consequently, material absorption losses play a minor role in the mid-IR in a few meter-long silica-based IC-HCPCF as demonstrated previously [5]. This suggests that the concept of hollow fiber gas laser (HOFGLAS), which was demonstrated in the visible with I 2 [6] and at 3 µm with C 2 H 2 pulsed [7] and CW [8], can be extended to longer wavelengths. Here, we report on an optically pumped gas-laser based on N 2 O-filled IC-HCPCF. The pulsed N 2 O HOFGLAS is pumped at 1.517 µm and emits at 4.6 µm with a photon conversion efficiency of 9% and a slope efficiency of 3%.

Fig. 1(a) shows schematically the experimental set-up and an N ₂ O energy level diagram with pump and laser transitions. A Kagome-lattice IC-HCPCF filled with a few tens of Torr of N 2 O is excited with an OPO. The latter is tuned to emit 8-ns pulses at 1.517 µm, in resonance with an N ₂ O second vibrational overtone transition, resulting in lasing on an R and P branch from the upper pump state. The fiber has a hypocycloid core-contour with an inner diameter of 85 µm, silica thickness of 490 nm and length of 45 cm. The fiber exhibits a propagation loss at the fundamental core mode (including silica material absorption) of ~30 dB/km at the pump wavelength, and of ~55 dB/m at 4.6 µm. The latter is significantly smaller than the estimated N ₂ O gain coefficient of ~400 dB/m. Figure 1(b) summarizes the results. The emission spectrum of the N 2 O HOFGLAS shown in the top left was obtained for 80 Torr of gas pressure and a pump energy of 1.3 µJ. It exhibits two unresolved lines at 4.595 µm and 4.655 µm that correspond to the P(17) and R(15) transition, respectively. The observed dependence of the laser output on gas pressure shows an optimum pressure of ~80 Torr. The laser threshold occurred at an absorbed pump energy of 150 nJ, and slope efficiency of 3% for a pump energy range of 0.1-2.5 µJ. Optimization of parameters such as the fiber length is likely to result in higher slope efficiency.

Funding: Air Force Research Lab (FA9451-17-2-0011) , College of Arts and Sciences at the University of New Mexico, région Nouvelle Aquitaine.

1. S. D. Jackson, Nature Photonics 6, pp. 423-431 (2012).

2. F. Couny et al., Science 318 (5853), pp. 1118-1121 (2007).

3. F. Benabid et al., J. Mod. Opt. 58 (2), pp. 87–124 (2011) 4. B. Debord et al., Optica 4 (2), pp. 209-217 (2017).

5. A. D. Pryamikov et al., Optics Express 19 (2), pp. 1441-1448 (2011).

6. A. V. V. Nampoothiri et al., Appl. Opt. 56 (34), pp. 9592-9595 (2017).

7. A. M. Jones et al., Optics Express 19 (3), pp.2309-2316 (2011).

8. M. R. A. Hassan et al. Optica 3 (3), pp. 218-221 (2016).

Fig. 1 (a) Schematics of the experimental set-up and conditions. (b) N 2 O HOFGLAS emission spectrum (top left), Measured N 2 O laser output as function of the pressure for 70 µJ of pump energy coupled into the fiber. The inset shows the

calculated gain coefficient as function of gas pressure. Laser pulse energy as a function of absorbed pump pulse energy.