Coherent blue emission induced by a combination of diode and femtosecond lasers

TL;DR

This paper demonstrates the generation of coherent blue light in rubidium vapor through the combined use of a femtosecond pulse train and a diode laser, revealing the role of induced atomic coherence and frequency comb structure.

Contribution

It introduces a novel method of producing blue emission by combining ultrashort pulses and continuous-wave lasers to excite specific atomic transitions and induce coherence.

Findings

Blue emission depends on atomic density with sharp growth and saturation.

The excitation spectrum shows a frequency comb structure.

Each mode of the comb induces a nonlinear process.

Abstract

We report the investigation of a collimated blue light generated in rubidium vapor due to the combined action of an ultrashort pulse train and a cw diode laser. Each step of the two-photon transition 5S - 5P$_{3/2}$ - 5D is excited by one of the lasers, and the induced coherence between the 5S and 6P$_{3/2}$ states is responsible for generating the blue beam. Measurements of the excitation spectrum reveal the frequency comb structure, indicating that each individual mode is responsible for inducing a nonlinear process. The strong signal dependency on the atomic density is characterized by a sharp growth and rapid saturation.