She is the founder of the Photon Factory laser lab at the University of Auckland and the chief science officer for two spin-off companies, Engender Technologies and Orbis Diagnostics.

[1] She has a strong focus on teaching, mentoring and public outreach and is an outspoken advocate for issues of gender equality and ethics in science.

[3] In 1983 Simpson gained a prestigious Echols scholarship at the University of Virginia, a unique undergraduate programme that encourages freedom of inquiry and critical thought.

[3][2] Her initial intention was to study medicine but the academic flexibility of the Echols programme allowed her to take a variety of subjects including history, civilisation and literature.

[3][4][2] She investigated how new-born rats pull immuno-globulins out of their mother's milk and into their bloodstream, learning to design and test experiments and use equipment like electron microscopes.

[7] Part way through her PhD studies Simpson moved from the medical school to a spectroscopy lab in the chemistry department at the University of New Mexico, shifting research focus and group.

[10][11] Her studies directly impacted phototherapeutics, molecular- and nano-scale electronic components, and unraveling the fundamental behaviour of photoactive systems.

[8][6] The photon factory's core mission is to enable the research of all New Zealand scientists – academic, industrial, government and student-led – through the advanced use of laser pulses to interrogate light-matter interactions and to manipulate and machine materials.

[8] The Photon factory's research specialises in using extremely short (femtosecond) laser pulses to solve both fundamental and applied problems.

These include micro-machining and micro-fabrication (cutting, making and shaping materials) as well as probing molecules in the millions of billionths of seconds after absorbing light.

They have also studied how pigments fade in art, investigated light-based cancer cures, developed a handheld device for diagnosing suspicious skin lesions and explored basic laser–material interactions.

[15] Simpson's work is internationally recognised for providing critical insight into how molecules and materials convert light into more useful types of energy, and applying this knowledge in new and exciting areas such as sperm sorting for the dairy industry.

[5] Simpson and her students use ultrafast laser spectroscopy to study rapidly evolving molecules as they convert light to more useful forms of energy.

She has given international talks and written articles on this topic and in 2016 hosted a delegation of top level Chinese government officials interested in improving productivity and health in the agricultural sector to the Photon Factory.

[21][22][23] Engender has developed a new technique to efficiently sort bull sperm by sex, which aims to give farmers greater genetic control over their herds and reduce the number of bobby calves that need to be killed.

[24] In 2016 Engender won the Agtech category of the Silicon Valley Forum Tech World Cup competition, the first ever win by an Australasian company.

Their aim is to develop a robust and disposable microfluidic disk that offers tests of medical laboratory precision in a time-sensitive manner at points-of-need in the community.

[33][34][35] From early in her career Simpson has emphasised the people-side of science and focused strongly on teaching, mentoring, ethics and public communication.

[12] At Case Western Reserve University she fostered innovation in undergraduate teaching, women in science, and ethics in education and research.

[5] At The University of Auckland has taught over 1200 science and non-science majors each year including large undergraduate courses and classes in the English Department linking physics and poetry.

She was one of the first two female chemists hired in the Chemistry Department at Case Western Reserve University and became involved in a US programme called ACES (Academic Careers in Engineering & Science) which aimed to achieve full participation of women at all levels of faculty and academic leadership in the science and engineering workforce.

[12] The Photon Factory's coordinated outreach efforts got started in 2015 when Simpson took the position of co-chair of the New Zealand International Year of Light Committee.

As part of the event Simpson's team ran art competitions, had a logo competition and engaged with the indigenous (Māori) community, to come up with a translation of “International Year of Light.” They ran outreach activities at eight museums across New Zealand and created low-cost take-home optics kits for children containing light-related hands-on experiments that were made available to tens of thousands of New Zealand children and youth.