The University of Southampton
University of Southampton Institutional Repository

Power Scaling of Mid-Infrared and Two-Micron Laser Sources

Power Scaling of Mid-Infrared and Two-Micron Laser Sources
Power Scaling of Mid-Infrared and Two-Micron Laser Sources
One of the most efficient methods for generating laser light in the 3–5 µm mid-infrared wavelength band involves the use of an optical parametric oscillator (OPO) to convert an incident pump photon into two longer-wavelength photons. By using a pump laser at a wavelength around 2 µm, both of the output photons from the OPO can be in the 3–5 µm band, greatly improving the conversion efficiency. Due to the nonlinear nature of the conversion process, a high-peak-power pump laser is essential for overcoming the large OPO threshold intensity, with pulsed lasers and amplifiers based on Ho:YAG being particularly attractive for such operation due to a natural emission peak at 2090 nm (where the absorption losses of OPO crystals are generally much lower than for shorter wavelengths) and a large energy storage capability. Ho:YAG sources are often pumped by continuous-wave thulium-doped fibre lasers in order to target the 1907 nm absorption line of the Ho:YAG crystals. However, all three stages (thulium fibre, Ho:YAG and OPO) suffer from a variety of intrinsic challenges that limit their operation at high average power levels, which have been investigated here.
A novel dopant distribution profile has been explored within the core region of a cladding-pumped thulium fibre laser in order to permit much longer device lengths to be utilised and greatly improve the thermal management at high power levels, without being hampered by the onset of long-wavelength parasitic lasing before 1907 nm emission can be achieved. Up to 131 W of continuous-wave 1907 nm output is demonstrated from a single 6-metre-long section of nested-ring thulium-doped fibre, with the potential for adapting the nested-ring design to target other wavelengths that are limited by parasitic lasing also being examined. A high power master-oscillator power-amplifier Ho:YAG source has been developed using a 23.7 W, 36 ns Q-switched Ho:YAG seed laser which is injected into a two-stage amplifier system. Two 160 W all-fibre 1907 nm thulium pump sources were developed to single-end-pump the two amplifier crystals and greatly reduce the system complexity in comparison to alternative 1907 nm pump sources, generating up to 85 W of 2.1 µm output.
The power scaling of radially polarised light at 2.1 µm has also been explored using Ho:YAG sources, including a 33.7 W double-pass thin-slab amplifier where the onset of depolarisation has been particularly targeted for mitigation. A 20.6 W radially polarised laser has also been demonstrated which uses an intra-cavity laser-written S-waveplate device to allow the simultaneous generation of radial polarisation and cavity Q-switching with up to 0.5 mJ pulse energy and a 210 ns pulse duration. Lastly, the potential advantages of using a highly-elliptical pump beam in a mid-infrared OPO are explored, initially by pumping the OPO directly with the 23.7 W Q-switched Ho:YAG seed laser, generating up to 3.7 W of mid-infrared output power for a 13:1 aspect ratio pump spot. The opportunity for further OPO power scaling when pumped with the 85 W MOPA output is also considered.
University of Southampton
Barber, Matthew James
5682d70c-71a4-4875-a714-55704b8ac20c
Barber, Matthew James
5682d70c-71a4-4875-a714-55704b8ac20c
Clarkson, William
3b060f63-a303-4fa5-ad50-95f166df1ba2
Shardlow, Peter
9ca17301-8ae7-4307-8bb9-371df461520c

Barber, Matthew James (2023) Power Scaling of Mid-Infrared and Two-Micron Laser Sources. University of Southampton, Doctoral Thesis, 176pp.

Record type: Thesis (Doctoral)

Abstract

One of the most efficient methods for generating laser light in the 3–5 µm mid-infrared wavelength band involves the use of an optical parametric oscillator (OPO) to convert an incident pump photon into two longer-wavelength photons. By using a pump laser at a wavelength around 2 µm, both of the output photons from the OPO can be in the 3–5 µm band, greatly improving the conversion efficiency. Due to the nonlinear nature of the conversion process, a high-peak-power pump laser is essential for overcoming the large OPO threshold intensity, with pulsed lasers and amplifiers based on Ho:YAG being particularly attractive for such operation due to a natural emission peak at 2090 nm (where the absorption losses of OPO crystals are generally much lower than for shorter wavelengths) and a large energy storage capability. Ho:YAG sources are often pumped by continuous-wave thulium-doped fibre lasers in order to target the 1907 nm absorption line of the Ho:YAG crystals. However, all three stages (thulium fibre, Ho:YAG and OPO) suffer from a variety of intrinsic challenges that limit their operation at high average power levels, which have been investigated here.
A novel dopant distribution profile has been explored within the core region of a cladding-pumped thulium fibre laser in order to permit much longer device lengths to be utilised and greatly improve the thermal management at high power levels, without being hampered by the onset of long-wavelength parasitic lasing before 1907 nm emission can be achieved. Up to 131 W of continuous-wave 1907 nm output is demonstrated from a single 6-metre-long section of nested-ring thulium-doped fibre, with the potential for adapting the nested-ring design to target other wavelengths that are limited by parasitic lasing also being examined. A high power master-oscillator power-amplifier Ho:YAG source has been developed using a 23.7 W, 36 ns Q-switched Ho:YAG seed laser which is injected into a two-stage amplifier system. Two 160 W all-fibre 1907 nm thulium pump sources were developed to single-end-pump the two amplifier crystals and greatly reduce the system complexity in comparison to alternative 1907 nm pump sources, generating up to 85 W of 2.1 µm output.
The power scaling of radially polarised light at 2.1 µm has also been explored using Ho:YAG sources, including a 33.7 W double-pass thin-slab amplifier where the onset of depolarisation has been particularly targeted for mitigation. A 20.6 W radially polarised laser has also been demonstrated which uses an intra-cavity laser-written S-waveplate device to allow the simultaneous generation of radial polarisation and cavity Q-switching with up to 0.5 mJ pulse energy and a 210 ns pulse duration. Lastly, the potential advantages of using a highly-elliptical pump beam in a mid-infrared OPO are explored, initially by pumping the OPO directly with the 23.7 W Q-switched Ho:YAG seed laser, generating up to 3.7 W of mid-infrared output power for a 13:1 aspect ratio pump spot. The opportunity for further OPO power scaling when pumped with the 85 W MOPA output is also considered.

Text
Matthew_Barber_Doctoral_Thesis_PDFA - Version of Record
Restricted to Repository staff only until 23 May 2024.
Available under License University of Southampton Thesis Licence.
Text
Final-thesis-submission-Examination-Mr-Matthew-Barber
Restricted to Repository staff only
Available under License University of Southampton Thesis Licence.

More information

Published date: 23 May 2023

Identifiers

Local EPrints ID: 477059
URI: http://eprints.soton.ac.uk/id/eprint/477059
PURE UUID: e7330d16-e107-40d2-8876-8aa6c5a43952
ORCID for Matthew James Barber: ORCID iD orcid.org/0000-0001-9768-6421
ORCID for Peter Shardlow: ORCID iD orcid.org/0000-0003-0459-0581

Catalogue record

Date deposited: 25 May 2023 16:36
Last modified: 20 Mar 2024 02:44

Export record

Contributors

Author: Matthew James Barber ORCID iD
Thesis advisor: William Clarkson
Thesis advisor: Peter Shardlow ORCID iD

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×