Laser frequency stabilization and spectroscopy at 2051 nm using a compact CO₂-filled Kagome hollow core fiber...

We describe a compact, all fiber, frequency stabilized diode laser system at 2051 nm using CO₂ gas-filled Kagome Hollow Core Fiber (HCF), capable of tuning continuously over four transitions in ¹²C¹⁶O₂: R(24), R(26), R(28), and R(30). This laser system has been designed for use in future space-based atmospheric monitoring using differential absorption lidar (DIAL). The fully spliced Kagome HCF gas cell is filled to 2 kPa CO₂ partial pressure and we compare the observed CO₂ lineshape features with those calculated using HITRAN, to quantify the properties of the CO₂-filled fiber cell. In this first demonstration of Kagome HCF used in a fully sealed gas cell configuration for spectroscopy at 2 µm, we characterize the frequency stability of the locked system by beat frequency comparison against a reference laser. Results are presented for the laser locked to the center of the ¹²C¹⁶O₂ R(30) transition, with frequency stability of ∼40 kHz or better at 1 s, and a frequency reproducibility at the 0.4-MHz level over a period of > 1 month. For DIAL applications, we also demonstrate two methods of stabilizing the laser frequency ~3 GHz from this line. Furthermore, no pressure degradation was observed during the ~15-month period in which frequency stability measurements were acquired.