Mukesh Kumar Shukla

Yb-fiber laser pumped high-power, broadly tunable, single-frequency red source based on a singly resonant optical parametric oscillator

We present an efficient and tunable source generating multi-watt single-frequency red radiation by intra-cavity frequency doubling of the signal in a MgO-doped periodically poled LiNbO3 (MgO:PPLN)-based singly resonant optical parametric oscillator (SRO). By optimally designing the SRO cavity in a six-mirror configuration, we generate ≈276  nm tunable idler radiation in mid-infrared with a maximum power of Pi=2.05  W at a pump power of Pp=14.0  W. The resonant signal is frequency doubled using a 10 mm-long BiB3O6 (BiBO) crystal which resulted in tunability of a red beam from ≈753 to 780 nm band with maximum power Pr≈4.0  W recorded at λr≈756  nm. The deployment of a six-mirror SRO ensures single-frequency generation of red across the entire tuning range by inducing additional losses to Raman modes of LiNbO3 and, thus, inhibiting their oscillation. Using a scanning Fabry-Perot interferometer (FPI), nominal linewidth of the red beam is measured to ≈3  MHz which changes marginally over the entire tuning range. Long-term (over 1 h) peak-to-peak frequency fluctuation of the generated red beam is estimated to be about 3.3 GHz under free-running conditions at Pp=14.0  W. The generated red beam is delivered in a TEM00 mode profile with M2≤1.32 at maximum power in a red beam.

Single-Pass Multi-Watt Second-Harmonic-Generation in Congruent and Stoichiometric LiTaO 3

We present a comparison of an efficient, single-pass second-harmonic-generation (SHG) of a continuous-wave Yb-fiber laser using a 1) congruently grown LiTaO3 crystal and 2) stoichiometrically grown LiTaO3 crystal. Using a Yb-fiber laser pump source delivering a single-frequency output of 40 W at 1064 nm, we have generated ~ 8.5 and 14.5 W of single-frequency green-radiation at 532 nm from 8 mol% MgO-doped periodically poled, congruently grown LiTaO3 (MgO:cPPLT) crystal and 0.5 mol% MgO-doped periodically poled, stoichiometrically grown LiTaO3 (MgO:sPPLT) crystal, respectively. We obtained SHG conversion efficiencies in excess of 24% for 5-cm long MgO:cPPLT and ≥36% for 3-cm long MgO:sPPLT. The impact of thermal dephasing was evident in variation of SH power in case of MgO:cPPLT crystal. However, the manifestations due to thermal effect were found out be significantly weaker in case of MgO:sPPLT. This lead to saturation of SHG efficiency at pump powers ≥20 W for MgO:cPPLT. The long-term peak-to-peak power-fluctuation in case of MgO:sPPLT is recorded to be ≈ 4 % for the green beam over a 4-h duration which shows improved performance over MgO:cPPLT output (peak-to-peak power-fluctuation ≈ 11 %). In addition, the 532-nm radiation exhibited single-frequency characteristics with linewidth of 12 MHz (MgO:cPPLT) and 5 MHz (MgO:sPPLT).

Refractive index sensor based on hybrid-Tamm plasmon-polariton and cavity mode

We propose the design of refractive index sensor using hybrid-modes formed due to coupling of Tamm-plasmon-polaritons (TPP) and cavity mode in Ta2O5/SiO2 based distributed Bragg-reflectors (DBR). The cavity mode sensitivity varied from 180 nm/RIU to 310 nm/RIU while the sensitivity of low frequency hybrid TPP mode varied from 70 nm/RIU to 210 nm/RIU.

Tamm plasmon polaritons in photonic quasi-crystals

We present a study on the realization of Tamm Plasmon-polariton in the metal deposited Fibonacci sequence based distributed Bragg reflector. All the simulated results are compared with the regular “DBR-matal” structure constructed with the same materials.

High power, tunable, Mid-IR generation with singly resonant optical parametric oscillator

We present a high power, single-frequency, continuously-tunable, singly-resonant optical parametric oscillator (SRO) based on 80 mm-long MgO-doped PPLN crystal pumped by a continuous-wave Yb-fiber laser. Four-mirror SRO ring-cavity configuration is tunable in the mid-infrared from 3761–3970 nm as well as in near-IR from 1453–1484 nm.

High-power frequency-doubled Yb-fiber laser

We report generation of 8.5W and 14.5W continuous-wave (cw) green radiation at 532nm by frequency-doubling of Yb-fiber laser using two different variants of LiTaO3 crystal with exceptionally good temporal and spatial features.

Measurement of nonlinear refractive index in open aperture Z-scan

We present an experimental study on measurement of nonlinear refractive index (n2) of organic liquids when the thermo-optic effects manifest into large nonlinear phase shifts ( φ0) in an open-aperture Z-scan configuration. Although we do not obtain the familiar peak–valley normalized transmittance curve as in the case of closed-aperture Z-scan technique, we use a theoretical model using Gaussian beam decomposition (GD) technique to estimate the value of n2. Using this recipe, we obtain the nonlinear refractive index n2 = −(4.90 ± 1.20) × 10−15 cm2/W for toluene (organic solvent) and n2 = −(10.60 ± 2.10) × 10−15 cm2/W for an organic polymer solution (10−4 M in toluene). By carrying out absorption measurements directly with an unfocussed Gaussian beam, we found nonlinear absorptions βtol = (2.42 ± 0.20) × 10−13 m/W and βpoly = (2.79 ± 0.24) × 10−13 m/W which are close to the expected results.