The University of Southampton
University of Southampton Institutional Repository

Power-scaling of diode-end-pumped solid-state lasers

Power-scaling of diode-end-pumped solid-state lasers
Power-scaling of diode-end-pumped solid-state lasers
This thesis presents a strategy for power-scaling diode-end-pumped solid-state lasers to multiwatt output power whilst retaining the high-efficiency and diffraction-limited beam quality, that have been characteristic of operation at low powers. This strategy reduces the detrimental effect of energy transfer upconversion (ETU), which can decrease the lifetime of the upper-laser-level and also increase the heat generated inside the laser material. An analytical description of the lifetime quenching and increased thermal lensing due to ETU is presented. Using this analytical model it is shown that ETU can be reduced by decreasing the absorption coefficient, by increasing the spot size or by decreasing the upconversion parameter, W. This strategy is applied to a Nd:YLF laser. Before designing the laser the published value of the upconversion parameter for Nd:YLF is confirmed as W = (1.7 ± 1) x 10-16cm3s-1, by observing the fluorescence saturation with increasing pump power. Also, without applying the power-scaling strategy, the thermal lensing in Nd:YLF in a typical pump set-up is determined, under lasing and non-lasing conditions. A significant difference between the thermal lensing under non-lasing and lasing conditions is observed which is attributed to the increase in heat input caused by ETU. In a standing-wave cavity, under cw lasing conditions and at the maximum pump power (29.5 W incident, 27.4 W absorbed) an output power of 11.1 W is obtained. This laser has excellent beam quality (M2x,y, < 1.1) throughout the pump power range. An intracavity-frequency doubled ring laser is also demonstrated. This laser produces >10W of single-frequency output with a 10% output coupler (~9.7 W at 1.053μm and ~0.6 W at 526.5 nm) at the maximum pump power. With a high reflector, for 1.053 μm, 6.2 W of polarised output (8.3 W generated inside the LBO), at 526.5nm is obtained. The output has excellent beam quality (M2x,y < 1.2) and amplitude stability (<± 0.5%). The mode-hopping suppression obtained in this laser is also investigated. A large tuning range (~42 GHz, ~80 axial mode-spacings) with the laser optimised for 1053nm output (i.e. with the 10% output coupler) is achieved with both diode-bars at full pump power. Also a large tuning range is achieved with the laser optimised for green output with one diode-bar (~72 GHz, ~150 axial mode-spacings). The upconversion problems are also sufficiently reduced to successfully demonstrate a highly efficient Q-switched ring laser. This laser overcomes the slow switching speed of the A-O modulator by taking the output through the diffracted beam. ~3.5mJ of single-frequency TEM00 energy for ~25W of incident pump power is demonstrated. This laser is then used to pump an OPO and preliminary results are presented.
Hardman, Paul Joseph
ef8cfc06-a8f0-4106-9185-a18edc75f946
Hardman, Paul Joseph
ef8cfc06-a8f0-4106-9185-a18edc75f946
Hanna, David
3da5a5b4-71c2-4441-bb67-21f0d28a187d

(1999) Power-scaling of diode-end-pumped solid-state lasers. University of Southampton, Optoelectronics Research Centre, Doctoral Thesis, 208pp.

Record type: Thesis (Doctoral)

Abstract

This thesis presents a strategy for power-scaling diode-end-pumped solid-state lasers to multiwatt output power whilst retaining the high-efficiency and diffraction-limited beam quality, that have been characteristic of operation at low powers. This strategy reduces the detrimental effect of energy transfer upconversion (ETU), which can decrease the lifetime of the upper-laser-level and also increase the heat generated inside the laser material. An analytical description of the lifetime quenching and increased thermal lensing due to ETU is presented. Using this analytical model it is shown that ETU can be reduced by decreasing the absorption coefficient, by increasing the spot size or by decreasing the upconversion parameter, W. This strategy is applied to a Nd:YLF laser. Before designing the laser the published value of the upconversion parameter for Nd:YLF is confirmed as W = (1.7 ± 1) x 10-16cm3s-1, by observing the fluorescence saturation with increasing pump power. Also, without applying the power-scaling strategy, the thermal lensing in Nd:YLF in a typical pump set-up is determined, under lasing and non-lasing conditions. A significant difference between the thermal lensing under non-lasing and lasing conditions is observed which is attributed to the increase in heat input caused by ETU. In a standing-wave cavity, under cw lasing conditions and at the maximum pump power (29.5 W incident, 27.4 W absorbed) an output power of 11.1 W is obtained. This laser has excellent beam quality (M2x,y, < 1.1) throughout the pump power range. An intracavity-frequency doubled ring laser is also demonstrated. This laser produces >10W of single-frequency output with a 10% output coupler (~9.7 W at 1.053μm and ~0.6 W at 526.5 nm) at the maximum pump power. With a high reflector, for 1.053 μm, 6.2 W of polarised output (8.3 W generated inside the LBO), at 526.5nm is obtained. The output has excellent beam quality (M2x,y < 1.2) and amplitude stability (<± 0.5%). The mode-hopping suppression obtained in this laser is also investigated. A large tuning range (~42 GHz, ~80 axial mode-spacings) with the laser optimised for 1053nm output (i.e. with the 10% output coupler) is achieved with both diode-bars at full pump power. Also a large tuning range is achieved with the laser optimised for green output with one diode-bar (~72 GHz, ~150 axial mode-spacings). The upconversion problems are also sufficiently reduced to successfully demonstrate a highly efficient Q-switched ring laser. This laser overcomes the slow switching speed of the A-O modulator by taking the output through the diffracted beam. ~3.5mJ of single-frequency TEM00 energy for ~25W of incident pump power is demonstrated. This laser is then used to pump an OPO and preliminary results are presented.

PDF
Hardman_1999_thesis_1340T.pdf - Other
Restricted to Repository staff only

More information

Published date: September 1999
Organisations: University of Southampton, Optoelectronics Research Centre

Identifiers

Local EPrints ID: 351506
URI: http://eprints.soton.ac.uk/id/eprint/351506
PURE UUID: f13686df-741b-43b4-af18-586285b5dfdc

Catalogue record

Date deposited: 13 May 2013 14:03
Last modified: 18 Jul 2017 04:25

Export record

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.

×