Brightness enhancement in a solid-state laser by mode transformation

Darryl Naidoo,Andrew Forbes,Igor A Litvin

doi:10.1364/optica.5.000836

Abstract

Laser brightness is a measure of the ability to deliver intense light to a target and encapsulates both the energy content and the beam quality. High-brightness lasers require that both parameters be maximized, yet standard laser cavities do not allow this. For example, multimode beams, a mix of many transverse modes, have a high energy content but low beam quality, while single transverse mode Gaussian beams have a good beam quality, but their small mode volume means a low energy extraction. Here we overcome this fundamental limitation and demonstrate an optimal approach to realizing high-brightness lasers. We employ intra-cavity beam shaping to produce a single transverse mode that changes profile inside the cavity, Gaussian at the output end and flattop at the gain end, such that both energy extraction and beam quality are simultaneously optimized. This work should have a significant influence on the design of future high-brightness laser cavities.

Highlights

The brightness of a laser source is a characteristic that encapsulates the energy or power content and the quality of the laser mode, requiring both to be optimized, i.e., maximal energy in a good beam quality
This can be expressed in terms of the beam quality factor, M2, as where M2 4πσσs∕λ πw0θ0∕λ, and σ represents the secondmoment real beam variance corresponding to the time-averaged intensity profile, while σs corresponds to the spatial frequency distribution, and λ represents the wavelength of the laser beam [1]
The resulting reflected beam was propagated to a pop-up flat mirror (PFM) that was positioned at 125 mm from the spatial light modulator (SLM) screen

Summary

Introduction

The brightness of a laser source is a characteristic that encapsulates the energy or power content and the quality of the laser mode, requiring both to be optimized, i.e., maximal energy in a good beam quality. The brightness, B, describes the potential of a laser beam to achieve high intensities while maintaining a large Rayleigh range for small focusing angles, which is strongly dependent on the quality of the transverse mode at the output and is defined as the power P emitted per unit surface area A per unit solid angle Ω. This can be expressed in terms of the beam quality factor, M2, as B P AΩ P M22λ2 (1).

Results

Discussion

Conclusion