Microjoule-level mid-infrared femtosecond pulse generation in hollow-core fibres

We demonstrate a fibre-based approach that generates mid-infrared femtosecond pulses in the 3-4 {\mu}m spectral region with microjoule-level single pulse energy. This is realised in a piece of gas-filled antiresonant hollow-core fibre that is pumped by a two-micron light source. A rapid variation of the dispersion near a structural resonance of the fibre creates a phase-matching point in the mid-infrared, which mediates the frequency-down conversion. We generate femtosecond pulses centred at 3.16 {\mu}m wavelength with the pulse energy of more than 1 {\mu}J, achieving the conversion efficiency as high as 9.4%. The wavelength of the radiation is determined solely by the dielectric wall thickness of the cladding elements, while the yield is subject to other experimental parameters. This, combined with high power-handling capability of hollow-core fibres, makes it possible to power scale the mid-infrared output by either increasing the pulse energy or repetition rate of the pump. The technique presents a new pathway to build an all-fibre-based mid-infrared supercontinuum source, which promises to be a powerful new tool for ultrahigh sensitivity molecular spectroscopy

A Fiber Bragg Grating—Bimetal Temperature Sensor for Solar Panel Inverters

This paper reports the design, characterization and implementation of a Fiber Bragg Grating (FBG)-based temperature sensor for an Insulted-Gate Bipolar Transistor (IGBT) in a solar panel inverter. The FBG is bonded to the higher Coefficient of Thermal Expansion (CTE) side of a bimetallic strip to increase its sensitivity. Characterization results show a linear relationship between increasing temperature and the wavelength shift. It is found that the sensitivity of the sensor can be categorized into three characterization temperature regions between 26 °C and 90 °C. The region from 41 °C to 90 °C shows the highest sensitivity, with a value of 14 pm/°C. A new empirical model that considers both temperature and strain effects has been developed for the sensor. Finally, the FBG-bimetal temperature sensor is placed in a solar panel inverter and results confirm that it can be used for real-time monitoring of the IGBT temperature

Dataset for mid IR gas laser

The data to generate figures 3 – 8: 1. Csv file (Figure 3(a)): contains the attenuations of the feedback fiber for figure 3(a) ; 2. Csv file (Figure 3(b)): contains the P(9) absorption line for figure 3 (b); 3. Csv file (Figure 4(a)): contains optical spectra for different pump transitions in figure 4(a); 4. Csv file (Figure 5(a)): contains the CW pump power/output power and stability of laser output as a function of time for figure 5(a); 5. Csv file (Figure 5(b)): contains the stability of laser output as a function of time for figure 5(b); 6. Csv file (Figure 5(b) inset): contains the mode profile of 3um laser for figure 5(b) inset; 7. Csv file (Figure 6): contains the Measured output power as a function of pump repetition rate for figure 6; 8. Csv file (Figure 7): contains pump power/output power at selected repetition rates shown in figure 7. 9. Zip file (Figure 8): contains csv file of radio frequency spectra (a), optical spectra (b) and time dependence (c) for the pump (blue) and the laser (red) at selected repetition rates shown in figure 8.The fiber attenuation was measured by using the cut-back method. The Tungsten lamp was used as the whitelight source. A 300 mm focal length scanning spectrometer (Bentham Instruments TMc300) was used for all spectral measurements at mid-infrared wavelengths, which has a 300 lines/mm grating and a liquid-nitrogen-cooled InAs detector (Electro-Optical Systems S-010-LN4). . The acetylene (12C2H2) P(9) absorption near 1530 nm was measured by recording the transmission of CW laser after 10 m gain fiber filled with 0.3 mbar acetylene gas. A thermal power meter (Ophir 3A-SH) was used to measure the laser power. The tunable laser diode (ID Photonics GMBH, CoBrite DX1, linewidth <100 kHz, maximum output power ~40 mW) was used as a source after amplification. All the pump powers shown in Figs 4 (a) and 6 were measured after the dichroic mirror with a thermal power meter (Ophir 3A-SH). Stability of laser output as a function of time in the fig 5 (b), was measured at 10 Hz sampling rate over more than one hour. A high gain detector (Thorlab PDA20H-EC) was used to directly measure the lasing power. The mode profile (inset Fig 5 (b)), was measured by using a two-dimensional scan with a short piece of feedback fiber (less than 3 m) across the output beam. The fiber was mounted on a 2D scanning translation device and connected with a high gain detector (Thorlab PDA20H-EC). The whole scan was controlled by LABView software. Time-dependent (Figs 8 (a & c)) measurements used a high speed HgCdTe detector (Vigo PVI-3.4-1×1- TO39-NO WINDOW-35, 1ns rise time) for 3.1 µm and a high speed InGaAs detector (Thorlabs DET01CFC) for 1.5 µm.A 350 MHz digital oscilloscope (Agilent InfiniiVision DSO-X-3032A) and 6 GHz spectrum analyzer (Agilent CSA Spectrum Analyzer) were used for measurement

Low-energy-threshold deep-ultraviolet generation in a small-mode-area hollow-core fiber

We demonstrate the generation of wavelength-tunable deep-ultraviolet pulses in a small-mode-area hollow-core fiber fabricated by tapering a nodeless tubular-type hollow-core fiber. Down-scaling of the cross-sectional geometry reduces the pump energy requirement for inducing sufficient nonlinear effects, presenting a unique opportunity for staging low-energy-threshold gas-based nonlinear optics. We report the onset of the ultraviolet light with the pump pulse energy as low as 125 nJ. Our numerical analysis shows that the frequency conversion arises due to soliton phase matching, and therefore shot-to-shot coherence of the ultraviolet emission is well-preserved. It offers a promising platform for a compact ultraviolet frequency comb source.Ministry of Education (MOE)Ministry of Education - Singapore (2020-T2- 2-026)

Anti-resonant hollow-core fiber fusion spliced to laser gain fiber for high-power beam delivery

We present the selective excitation of the fundamental mode in an anti-resonant hollow-core fiber (ARHCF) fusion-spliced with a commercial large mode area (LMA) fiber. By designing and fabricating a single-ring ARHCF that is mode-matched to a LMA fiber and by splicing the two using a CO2 laser-based splicer, we achieve a coupling efficiency of 91.2% into the fundamental mode. We also demonstrate an all-fiber integration of an ARHCF with a commercial ytterbium-doped fiber in a laser cavity for beam delivery application. Coupling of the single-mode laser output beam into the fundamental mode of the ARHCF is demonstrated with 90.4% efficiency (<0.45dB loss) for up to 50 W continuous wave beam in a stable and alignment-free all-fiber laser setup.National Research Foundation (NRF)Submitted/Accepted versionNational Research Foundation Singapore, Quantum Engineering Programme