EXHIBIT 23.1

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the Registration Statement
Numbers 333-43080, 333-76849 and 333-73666 on Form S-8 of GSI Lumonics Inc., of
our report dated December 15, 2003 on the financial statements of MicroE Systems
for the years ended September 28, 2003 and September 29, 2002 appearing in this
Current Report on Form 8-K/A Amendment No. 2 of GSI Lumonics Inc. dated July 28,
2004.

/s/ Deloitte & Touche LLP

Boston, Massachusetts
July 27, 2004