Acquisitions - Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Business Acquisition [Line Items]
Revenue	$ 97,716	$ 45,318
Cost of revenue	74,323	41,252
Gross profit	23,393	4,066
Operating expense:
Selling, general, and administrative	32,731	28,224
Research and development	17,910	13,782
Severance	27	140
Gain on sale of assets	(1,147)	0
Impairment charge	22,612	2,956
Total operating expense	72,133	45,102
Operating loss	(48,740)	(41,036)
Other (expense) income:
Interest expense, net	751	35
Foreign exchange loss	(1)	0
Total other (expense) income	(631)	136
Loss from continuing operations before income tax (expense) benefit	(49,371)	(40,900)
Income tax (expense) benefit from continuing operations	(42)	139
Net loss	(75,359)	(24,333)
Comprehensive loss	$ (75,450)	$ (23,892)
Net loss per basic share (in dollars per share)	$ (1.46)	$ (0.65)
Weighted-average number of basic shares and preferred warrants outstanding (in shares)	51,510	37,269
Weighted-average number of diluted shares and preferred warrants outstanding (in shares)	51,510	37,269
Pro Forma
Business Acquisition [Line Items]
Revenue	$ 149,786
Cost of revenue	114,516
Gross profit	35,270
Operating expense:
Selling, general, and administrative	38,862
Research and development	22,290
Severance	1,353
Gain on sale of assets	(2,685)
Impairment charge	2,956
Total operating expense	62,776
Operating loss	(27,506)
Other (expense) income:
Interest expense, net	(1,199)
Foreign exchange loss	(352)
Other income	148
Other income	137
Total other (expense) income	(1,266)
Loss from continuing operations before income tax (expense) benefit	(28,772)
Income tax (expense) benefit from continuing operations	78
Net loss	(28,694)
Foreign exchange translation adjustment	172
Pension adjustment	441
Comprehensive loss	$ (28,081)
Net loss per basic share (in dollars per share)	$ (0.77)
Weighted-average number of basic shares and preferred warrants outstanding (in shares)	37,269
Weighted-average number of diluted shares and preferred warrants outstanding (in shares)	37,269
Pro Forma | Pro Forma Adjustments
Business Acquisition [Line Items]
Revenue	$ 0
Cost of revenue	683
Gross profit	(683)
Operating expense:
Selling, general, and administrative	(4,102)
Research and development	(1,057)
Severance	0
Gain on sale of assets	0
Impairment charge	0
Total operating expense	(5,159)
Operating loss	4,476
Other (expense) income:
Interest expense, net	(1,060)
Foreign exchange loss	0
Other income	0
Other income	0
Total other (expense) income	(1,060)
Loss from continuing operations before income tax (expense) benefit	3,416
Income tax (expense) benefit from continuing operations	(19)
Net loss	3,397
Foreign exchange translation adjustment	0
Pension adjustment	0
Comprehensive loss	$ 3,397
Net loss per basic share (in dollars per share)	$ 0
Weighted-average number of basic shares and preferred warrants outstanding (in shares)	0
Weighted-average number of diluted shares and preferred warrants outstanding (in shares)	0
Pro Forma | EMCORE (excluding EMCORE Chicago)
Business Acquisition [Line Items]
Revenue	$ 118,029
Cost of revenue	89,486
Gross profit	28,543
Operating expense:
Selling, general, and administrative	33,294
Research and development	18,401
Severance	1,357
Gain on sale of assets	(2,685)
Impairment charge	2,956
Total operating expense	53,323
Operating loss	(24,780)
Other (expense) income:
Interest expense, net	(139)
Foreign exchange loss	(352)
Other income	148
Other income	0
Total other (expense) income	(343)
Loss from continuing operations before income tax (expense) benefit	(25,123)
Income tax (expense) benefit from continuing operations	139
Net loss	(24,984)
Foreign exchange translation adjustment	172
Pension adjustment	441
Comprehensive loss	$ (24,371)
Net loss per basic share (in dollars per share)	$ (0.67)
Weighted-average number of basic shares and preferred warrants outstanding (in shares)	37,269
Weighted-average number of diluted shares and preferred warrants outstanding (in shares)	37,269
Pro Forma | EMCORE Chicago
Business Acquisition [Line Items]
Revenue	$ 31,757
Cost of revenue	24,347
Gross profit	7,410
Operating expense:
Selling, general, and administrative	9,670
Research and development	4,946
Severance	(4)
Gain on sale of assets	0
Impairment charge	0
Total operating expense	14,612
Operating loss	(7,202)
Other (expense) income:
Interest expense, net	0
Foreign exchange loss	0
Other income	0
Other income	137
Total other (expense) income	137
Loss from continuing operations before income tax (expense) benefit	(7,065)
Income tax (expense) benefit from continuing operations	(42)
Net loss	(7,107)
Foreign exchange translation adjustment	0
Pension adjustment	0
Comprehensive loss	$ (7,107)