Revenue Recognition Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Oct. 03, 2020	Jul. 04, 2020	Apr. 04, 2020	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Oct. 03, 2020	Sep. 28, 2019	Sep. 29, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 316,751	$ 298,330	$ 293,147	$ 320,771	$ 335,464	$ 339,170	$ 372,860	$ 383,146	$ 1,228,999	$ 1,430,640	$ 1,902,573
OEM Laser Sources
Disaggregation of Revenue [Line Items]
Net sales									758,929	886,676	1,259,477
Industrial Lasers & Systems
Disaggregation of Revenue [Line Items]
Net sales									470,070	543,964	643,096
Products | OEM Laser Sources
Disaggregation of Revenue [Line Items]
Net sales									441,476	532,863	890,591
Products | Industrial Lasers & Systems
Disaggregation of Revenue [Line Items]
Net sales									369,342	430,878	512,818
Other products and services revenues | OEM Laser Sources
Disaggregation of Revenue [Line Items]
Net sales									317,453	353,813	368,886
Other products and services revenues | Industrial Lasers & Systems
Disaggregation of Revenue [Line Items]
Net sales									100,728	113,086	130,278
Sales of spare parts
Disaggregation of Revenue [Line Items]
Net sales									62,400
Microelectronics | OEM Laser Sources
Disaggregation of Revenue [Line Items]
Net sales									466,780	568,387	951,166
Microelectronics | Industrial Lasers & Systems
Disaggregation of Revenue [Line Items]
Net sales									71,755	63,789	85,188
Materials processing | OEM Laser Sources
Disaggregation of Revenue [Line Items]
Net sales									36,129	38,017	46,467
Materials processing | Industrial Lasers & Systems
Disaggregation of Revenue [Line Items]
Net sales									299,621	366,861	474,437
OEM components and instrumentation | OEM Laser Sources
Disaggregation of Revenue [Line Items]
Net sales									158,748	163,095	140,616
OEM components and instrumentation | Industrial Lasers & Systems
Disaggregation of Revenue [Line Items]
Net sales									89,799	103,693	80,207
Scientific and government programs | OEM Laser Sources
Disaggregation of Revenue [Line Items]
Net sales									97,272	117,177	121,228
Scientific and government programs | Industrial Lasers & Systems
Disaggregation of Revenue [Line Items]
Net sales									$ 8,895	$ 9,621	$ 3,264