Raman shifter optimized for lidar at a 1.5 microm wavelength

Area of Science:

• Nonlinear Optics
• Laser Technology
• Photonics

Background:

• Raman shifters are crucial for generating specific laser wavelengths.
• Optimizing high-energy pulse generation at 1.54 micrometers presents significant challenges.

Purpose of the Study:

• To optimize a Raman shifter for efficient generation of high-energy laser pulses at 1.54 micrometers.
• To detail a novel forward-scattering design for enhanced performance.

Main Methods:

• Utilized a forward-scattering design with multiple passes and a nonfocused optical configuration.
• Implemented Stokes injection seeding and internal gas recirculation.
• Employed a single longitudinal mode Nd:YAG laser for pumping and a narrowband laser diode for seeding.

Main Results:

• Achieved first-Stokes conversion efficiencies up to 43% (62% photon conversion efficiency).
• Demonstrated output average power exceeding 17.5 W and pulse energies of 350 mJ at 50 Hz.
• Obtained good beam quality with M2<6 and narrow bandwidth, tunable output.

Conclusions:

• The optimized Raman shifter design successfully generates high-energy laser pulses at 1.54 micrometers.
• The system offers high efficiency, substantial power, and excellent beam quality.
• The use of narrowband seeding enables tunable output, expanding application possibilities.