Walsh was born on 19 December 1916 and brought up in
Hoddlesden, a small village about twenty miles from
Manchester. He was the eldest son of Thomas Haworth Walsh, cotton mill manager, and Betsy Alice (née Robinson). From the age of ten Walsh attended the
local grammar school in the nearby town of
Darwen, where he passed the Northern Universities Matriculation examination in 1933 and the Higher School Certificate examination in 1935. He then went to the
University of Manchester to read physics. On graduation in 1938 he was also awarded a research scholarship, which he took up in the physics department, where he was particularly influenced by
Henry Lipson’s suggestion that he work on the structure of
β-carotene. Walsh spent on year at Manchester working on this, before moving to the physics section of the
British Non-Ferrous Metals Research Association (BNF) in London, where he continued the theoretical work on the analysis. He was awarded an MSc (Tech) in 1944. While developing the method he discovered that it could not always be transferred uniformly from one laboratory to another, so he set about devising a General Purpose Source Unit. This generated a stable and reproducible source of discharge, essential in spectrographic emission work. He then assisted
Hilger & Watts Ltd to develop a commercial version. In 1945 Alan applied for the post of Research Officer for Spectroscopic Investigations at the
Council for Scientific and Industrial Research (CSIR) in
Melbourne. After a long delay, he was offered the job in March 1946, but he first had to spend 3–4 months in
Gordon Sutherland’s lab in Cambridge, to gain experience in the new field of infrared molecular spectroscopy. This led to a paper on the structure of phthiocerane, the hydrocarbon derived from phthiocerol, found in tubercle bacilli. Walsh arrived at CSIR, via laboratory visits in the USA, in April 1947. He set about installing the first operating infrared spectrometer in Australia, a
Perkin-Elmer Model 12B. He soon realised that its resolution was insufficient for any but the lightest molecules, so he devised and patented a double-pass system, which was licensed to Perkin-Elmer. Walsh is probably best known for his development of atomic absorption spectroscopy as an analytical tool. This is a complex story, recounted in detail by
Hannaford. He retired from CSIRO on 5 January 1977, and in June was created a
Knight Bachelor. In 1982 he was invited back to CSIRO as a senior research fellow. ==Honours, awards, affiliations and degrees==