1.645†µm Er:YAG single-mode dual-wavelength emitter for CH4 differential absorption lidar.

We present a hybrid fiber/bulk laser source at 1.645 µm designed for methane (CH4) monitoring using differential absorption lidar (DIAL) measurements in the atmosphere. The emitter is also suited for coherent wind Doppler lidar. It relies on a Q-switched Er:YAG ring cavity pumped by erbium fiber lasers at 1532 nm. The pulsed laser is sequentially seeded by two fiber-coupled CW distributed feedback (DFB) laser diodes in the center of the CH4 line multiplet at 1645.55 nm (ON wavelength) and out of at 1645.30 nm (OFF wavelength). Despite a gain difference in the crystal between the ON and OFF wavelengths, pulses with equal energies and durations (9 mJ/300 ns) are obtained at a rate of 1 kHz. The spectral stability and purity properties in the dual-wavelength operating regime are presented.

Hybrid fiber/bulk laser source designed for CO2 and wind measurements at 2.05 µm: publisher's note.

This publisher's note contains a correction to Opt. Lett.49, 969 (2024)10.1364/OL.510598.

Hybrid fiber/bulk laser source designed for CO2 and wind measurements at 2.05†µm.

We present a hybrid fiber/bulk laser source designed for CO2 and wind monitoring using differential absorption LIDAR (DIAL) and coherent detection at 2.05 µm. This source features a master oscillator power amplifier (MOPA) architecture made of four fiber stages and one single-pass, end-pumped, bulk amplifier. This Letter focuses on the single-pass bulk amplifier performance and on the hybrid architecture benefits for DIAL and coherent detection. The bulk material is a holmium-doped YLF crystal that provides high efficiency amplification at 2.05 µm. This laser offers an energy breakthrough as compared to the classical stimulated Brillouin scattering (SBS) limit encountered in a fiber laser without compromising robustness, thanks to very few free-space optical elements and a small optical path. It delivers pulse energy and repetition frequency of 9.0 or 1.2 mJ/20 kHz with 200 ns quasi Fourier-transform limited pulses.

2-µm double-pulse single-frequency Tm:fiber laser pumped Ho:YLF laser for a space-borne CO2 lidar.

In the framework of space-borne CO2 lidar development, the transmitter is a critical unit. We report on the development and the assessment of performances of a 2-µm single-frequency thulium fiber laser pumped Q-switched Ho:YLF laser. To fulfill the requirements of space-based operation, a master oscillator power amplifier architecture has been chosen, and the oscillator works in double-pulse operation. The transmitter can generate a single-mode dual wavelength emission "ON" and "OFF" around the R30e line of the 20013←00001 band of CO212. It delivers a pair of OFF-ON pulses with 12 mJ and 42 mJ energy, respectively, at a pulse repetition frequency of 303.5 Hz. The pulse energy and central frequency stabilities are especially documented as well as pulse duration, polarization, overall efficiency, beam quality, pointing stability, and spectral purity. The possible limitations by light-induced damage or radiation-induced attenuation on the laser performances are also evaluated.

Evaluation of a HgCdTe e-APD based detector for 2 µm CO2 DIAL application.

Benefiting from close to ideal amplification properties (high gain, low dark current, and low excess noise factor), HgCdTe electron initiated avalanche photodiode (e-APD) technology exhibits state of the art sensitivity, thus being especially relevant for applications relying on low light level detection, such as LIDAR (Light Detection And Ranging). In addition, the tunable gap of the Hg1-xCdxTe alloy enables coverage of the short wavelength infrared (SWIR) and especially the 2 µm spectral range. For these two reasons, a HgCdTe e-APD based detector is a promising candidate for future differential absorption LIDAR missions targeting greenhouse gas absorption bands in SWIR. In this study, we report on the design and evaluation of such a HgCdTe e-APD based detector. The first part focuses on detector architecture and performance. Key figures of merit are: 2.8 µm cutoff wavelength, 200 µm diameter almost circular sensitive area, 185 K operating temperature (thermo-electric cooling), 22 APD gain (at 12 V reverse bias), 360 kΩ transimpedance gain, and 60 fWHz-0.5 noise equivalent power (at 12 V reverse bias). The second part presents an analysis of atmospheric LIDAR signals obtained by mounting the HgCdTe e-APD based detector on the 2 µm differential absorption LIDAR developed at the Laboratoire de Météorologie Dynamique and dedicated to CO2 monitoring. Discussion emphasizes random and systematic errors in LIDAR measurements regarding breadboard detector characterization. In particular, we investigate the influence of parasitic tails in detector impulse response on short range DIAL measurements.

An a posteriori method based on photo-acoustic cell information to correct for lidar transmitter spectral shift: application to atmospheric CO(2) differential absorption lidar measurements.

An a posteriori corrective method based on photo-acoustic cell (PAC) information is proposed to correct for laser transmitter spectral shift during atmospheric CO(2) measurements by 2 microm heterodyne differential absorption lidar (HDIAL) technique. The method for using the PAC signal to retrieve the actual atmospheric CO(2) absorption is presented in detail. This issue is tackled using a weighting function. The performance of the proposed corrective method is discussed and the various sources of error associated with the PAC signal are investigated. For 300 shots averaged and a frequency shift (from the CO(2) absorption line center) lower than the CO(2) absorption line half-width, the relative error on HDIAL CO(2) mixing ratio measurements is lower than 1.3%. The corrective method is validated in absolute value by comparison between HDIAL and in situ sensor measurements of CO(2).