A deep ultraviolet laser light source by frequency doubling of GaN based external cavity diode laser radiation

Ruhnke, Norman

• Publisher: Cuvillier Verlag
• Year: 2022
• eBook ISBN:
  9783736966130
• Print ISBN:
  9783736976139
• Edition: 1

A compact and portable laser light source emitting in the wavelength range between 210 nm and 230 nm would enable numerous applications outside of laboratory environments, such as sterilization and disinfection of medical equipment, water purification or gas and air analysis using absorption spectroscopy. Such a source is also highly attractive for the identification and quantification of proteins and biomolecules by means of laser-induced fluorescence or Raman spectroscopy.In this thesis, a novel concept to realize such a compact and portable laser light source with low power consumption and an emission around 222 nm is investigated. The developed concept is based on single-pass frequency doubling of a commercially available high-power GaN laser diode emitting in the blue spectral range.Due to the low frequency doubling conversion efficiencies in this wavelength range of about 10-4 W-1, a laser diode with high optical output power above 1 W is required as pump source. Moreover, it has to exhibit narrowband emission in the range of the acceptance bandwidth of the applied nonlinear BBO crystal.Since GaN-based high-power laser diodes typically show broad emission spectra of ?? = 1...2 nm, stabilizing and narrowing their wavelength by using external wavelength-selective elements is investigated and presented for the first time.With the understanding for the novel concept gained in this work, a compact ultraviolet laser light source was realized. It has a power consumption of less than 10 W and is exceptionally robust due to its immoveable components. The demonstrated output power of 160 ?W enables numerous industrial and everyday applications for which previous laser systems have been too complex and overly cost- and energy-intensive.

Table of contents

• 1 Introduction
• 2 Fundamentals for frequency doublingwith GaN based laser diodes
• 2.1 Nonlinear optics
• 2.2 Nonlinear materials for deep ultraviolet light generation
• 2.3 Birefringent phase matching in BBO
• 2.4 Second harmonic generation with focused Gaussianbeams
• 3 Characterization of the applied laserdiode
• 3.1 Working principle of laser diodes and vertical layerstructure
• 3.2 Longitudinal modes
• 3.3 Optical gain and threshold condition
• 3.4 Electro-optical characteristics
• 3.5 Spectral emission characteristics
• 3.6 Spatial emission characteristics
• 3.7 Implications for the development of a deep ultravioletlaser light source
• 4 External cavity diode lasers as pumpsources for DUV generation
• 4.1 Wavelength stabilization by external optical feedback
• 4.2 Macroscopic external cavity diode laser in Littrowconfiguration
• 4.3 Volume-Bragg-Grating stabilized external cavity diodelaser module (μECDL)
• 4.4 Summary
• 5 Compact deep ultraviolet laser lightsource
• 5.1 Proof-of-concept setup with macroscopic ECDL aspump source
• 5.2 Micro-integrated ECDL module as pump source
• 6 Conclusion and Outlook
• A Datasheet information for laser diodePL TB450B (Osram OptoSemiconductors GmbH)
• Bibliography
• List of Figures
• List of Tables