The lidar emitter is a diode‑pumped, single‑longitudinal‑mode Alexandrite ring laser with optional intra‑cavity second harmonic generation:
- IR version: ~770 nm emission
- UV version: intra‑cavity frequency doubling in an LBO crystal, emitting at 385.991 nm in a deep Fraunhofer line
The same resonator design is used for both versions; only the nonlinear crystal and output coupler differ. Intracavity SHG keeps the fluence in the crystal far below damage thresholds while providing pulse energies suitable for lidar.
Final performance (prototype UV laser):
- Wavelength: 385.991 nm (tunable over >10 GHz)
- Pulse energy: ~2.5 mJ at 750 Hz (~1.9 W average power)
- Electro‑optical efficiency: ~2 %
- Pulse duration: ~0.8 µs (sets altitude resolution)
- Beam quality: M² ≈ 1.1 in both axes
- Frequency jitter: <1 MHz with the novel seeder laser
- Spectral bandwidth: ≪20 pm (limited by the measurement setup; narrow enough for Doppler‑Rayleigh)
The laser head is mounted on an aluminium breadboard and enclosed in a sealed housing with decoupled mechanical interfaces so that thermo‑mechanical stress on the housing does not disturb internal alignment. IR and UV prototypes have been transported throughout Europe and integrated into the lidar without needing realignment; performance remains unchanged after long transports and months of operation.
