Segment and Geographic Information - Sales and Income (Loss) from Operations (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Apr. 03, 2021 USD ($)	Apr. 04, 2020 USD ($)	Apr. 03, 2021 USD ($) segments	Apr. 04, 2020 USD ($)
Segment Reporting [Abstract]
Number of reporting segments | segments			2
Segment Reporting Information [Line Items]
Net sales	$ 373,982	$ 293,147	$ 700,035	$ 613,918
Total loss from operations	(196,236)	(449,311)	(179,286)	(438,721)
Total other expense, net	(2,526)	(5,663)	(4,815)	(8,697)
Loss before income taxes	(198,762)	(454,974)	(184,101)	(447,418)
OEM Laser Sources
Segment Reporting Information [Line Items]
Net sales	223,248	173,722	434,410	374,670
Income (loss) from operations:	51,627	35,469	101,043	83,177
Industrial Lasers & Systems
Segment Reporting Information [Line Items]
Net sales	150,734	119,425	265,625	239,248
Income (loss) from operations:	2,603	(471,845)	(5,309)	(492,145)
Corporate and other
Segment Reporting Information [Line Items]
Income (loss) from operations:	$ (250,466)	$ (12,935)	$ (275,020)	$ (29,753)