Increased wavelength options in the visible and ultraviolet for Raman lasers operating on dual Raman modes

R P Mildren,J A Piper

doi:10.1364/oe.16.003261

Abstract

We report increased wavelength options from Raman lasers for Raman media having two Raman modes of similar gain coefficient. For an external-cavity potassium gadolinium tungstate Raman laser pumped at 532 nm, we show that two sets of Stokes orders are generated simultaneously by appropriate orientation of the Raman crystal, and also wavelengths that correspond to sums of the two Raman modes. Up to 14 visible Stokes lines were observed in the wavelength range 555-675 nm. The increase in Stokes wavelengths also enables a much greater selection of wavelengths to be accessed via intracavity nonlinear sum frequency and difference frequency mixing. For example, we demonstrate 30 output wavelength options for a wavelength-selectable 271-321 nm Raman laser with intracavity sum frequency mixing in BBO. We also present a theoretical analysis that enables prediction of wavelength options for dual Raman mode systems.

Highlights

Nonlinear methods for shifting the output wavelength of lasers are needed in a host of industrial and scientific laser applications that require more wavelength specificity than that provided by existing laser sources and their harmonics[1]
Ammann[21] first reported a Raman laser with intracavity sum frequency mixing in an arclamp pumped Nd:YALO laser which included an intracavity lithium iodate crystal which simultaneously acted as a Raman and nonlinear harmonic generation
Twenty lines were observed with UV output wavelengths involving second and third order excitation of the μ2 Raman mode

Summary

Introduction

Nonlinear methods for shifting the output wavelength of lasers are needed in a host of industrial and scientific laser applications that require more wavelength specificity than that provided by existing laser sources and their harmonics[1]. The cascade to higher order Stokes wavelengths inside a Raman resonator is rapid and good temporal overlap is obtained between the intracavity fields within a 10ns pump pulse This enables conversion to other wavelength regions via second-harmonic, sum and difference frequency generation. Systems that use separate Raman and nonlinear crystals, along with the increased availability of high quality Raman materials and diode pumped solid-state lasers, has seen wavelength switchable lasers in the visible[22] and in the ultraviolet (270-320nm)[12] In all of these systems, wavelength selectability arises from the cascading of energy from the fundamental into higher Stokes orders and the nonlinear output coupling at the selected harmonic combination by appropriate configuration of the phase-matching conditions in the nonlinear harmonic mixing crystal (eg., by temperature or angle tuning). As far as the authors are aware, only sum frequency (SF) and second harmonic (SH) wavelengths have been demonstrated to date, the concept can be extended to generate long wavelengths via difference frequency (DF) generation

Results

Discussion

Conclusion