Upconversion and reduced 4F(3/2) upper-state lifetime in intensely pumped Nd:YLF

Area of Science:

• Laser physics
• Solid-state spectroscopy
• Materials science

Background:

• Neodymium-doped Yttrium Lithium Fluoride (Nd:YLF) is a crucial laser material.
• Understanding excited-state dynamics is vital for optimizing laser performance.
• High population inversions can lead to complex decay mechanisms.

Purpose of the Study:

• To investigate the nonexponential decay of the 4F(3/2) upper laser state in Nd:YLF.
• To identify the underlying mechanisms responsible for the observed decay kinetics.
• To evaluate key parameters related to energy transfer processes.

Main Methods:

• Time-resolved fluorescence spectroscopy.
• Small-signal gain probes.
• Analysis of decay kinetics under intense Q-switched laser pumping.

Main Results:

• Observed nonexponential decay of the 4F(3/2) state in low-doped Nd:YLF.
• Identified a migration-assisted energy-transfer upconversion (ETU) phase in the hopping regime.
• Quantified the macroscopic ETU coefficient (alpha2) as (0.98 +/- 0.03) x 10(-16) cm3/s.
• Estimated ETU and migration microparameters (C(da)* and C(dd)).

Conclusions:

• Rate-equation treatments are not strictly valid for intensely pumped Nd:YLF due to the identified ETU process.
• The study provides crucial insights into the energy transfer dynamics in Nd:YLF lasers.
• The findings are important for the design and operation of high-power solid-state lasers.