Methods towards improving the temporal stability of a femtosecond field synthesizer
File(s)
Author(s)
Turner, James
Type
Thesis
Abstract
Multi-colour femtosecond waveforms can be used to enhance the energy and efficiency of photons generated by high harmonic generation (HHG), which may provide significant benefits for ultrafast spectroscopy and allow for targeted transitions within complex molecular structures.
In this doctoral thesis I present experimental work done to facilitate the inclusion of a short-wave infrared component into a femtosecond field synthesizer including methods to characterise the pulses and improve the phase stability of the synthesizer.
We have developed an optical system that splits the 30 fs, 800 nm output from a Ti:Sapphire laser amplifier system to generate a 6.2 fs few-cycle (FC) pulse, centered at 800 nm, an ultraviolet (UV) pulse, at 400 nm, and a short-wave infrared (SWIR) pulse generated by an optical parametric amplifier (OPA), at 1300 nm. For characterisation of the SWIR field, a second harmonic/ transient grating (SH/TG) frequency resolved optical gating (FROG) was constructed and tested revealing that the 1300 nm pulse has a duration of 50 ± 5 fs, whilst the pump beam that seeds the generation of the few-cycle pulse has a duration of 38 ± 3 fs. Timing jitter introduced by the OPA means that additional phase-stabilisation was required between the few-cycle and SWIR pulses. Therefore, a balanced optical cross-correlator (BOC) that mixes the residual pump from the OPA and SWIR beams was constructed, with preliminary tests showing the successful detection of a sum-frequency generation signal that can provide an error signal to a feedback system.
The construction and implementation of a dual SH/TG FROG for characterisation of 800 nm, 400 nm, and 1300 nm with minimal adjustment needed has, to the best of our knowledge, not been previously done. Furthermore, the use of a BOC into a three-channel synthesizer consisting of these wavelengths is, as far as we know, a novel concept.
In this doctoral thesis I present experimental work done to facilitate the inclusion of a short-wave infrared component into a femtosecond field synthesizer including methods to characterise the pulses and improve the phase stability of the synthesizer.
We have developed an optical system that splits the 30 fs, 800 nm output from a Ti:Sapphire laser amplifier system to generate a 6.2 fs few-cycle (FC) pulse, centered at 800 nm, an ultraviolet (UV) pulse, at 400 nm, and a short-wave infrared (SWIR) pulse generated by an optical parametric amplifier (OPA), at 1300 nm. For characterisation of the SWIR field, a second harmonic/ transient grating (SH/TG) frequency resolved optical gating (FROG) was constructed and tested revealing that the 1300 nm pulse has a duration of 50 ± 5 fs, whilst the pump beam that seeds the generation of the few-cycle pulse has a duration of 38 ± 3 fs. Timing jitter introduced by the OPA means that additional phase-stabilisation was required between the few-cycle and SWIR pulses. Therefore, a balanced optical cross-correlator (BOC) that mixes the residual pump from the OPA and SWIR beams was constructed, with preliminary tests showing the successful detection of a sum-frequency generation signal that can provide an error signal to a feedback system.
The construction and implementation of a dual SH/TG FROG for characterisation of 800 nm, 400 nm, and 1300 nm with minimal adjustment needed has, to the best of our knowledge, not been previously done. Furthermore, the use of a BOC into a three-channel synthesizer consisting of these wavelengths is, as far as we know, a novel concept.
Version
Open Access
Date Issued
2024-04-10
Date Awarded
01/01/2025
License URL
Advisor
Tisch, Professor John
Grant Number
EPSRC EP/N018680/1
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)