Document and Entity Information	3 Months Ended
	Dec. 31, 2011	Jan. 27, 2012
Entity Information [Line Items]
Entity Registrant Name	COHERENT INC
Trading Symbol	COHR
Entity Central Index Key	0000021510
Document Type	10-Q
Document Period End Date	Dec. 31, 2011
Amendment Flag	false
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--09-29
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		23,559,776