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As a branch of laser powder bed fusion, selective laser sintering (SLS) with femtosecond (fs) lasers and metal nanoparticles (NPs) can achieve high precision and dense submicron features with reduced residual stress, due to the extremely short pulse duration. Successful sintering of metal NPs with fs laser is challenging due to the ablation caused by hot electron effects. In this study, a double-pulse sintering strategy with a pair of time- delayed fs-laser pulses is proposed for controlling the electron temperature while still maintaining a high enough lattice temperature. We demonstrate that when delay time is slightly longer than the electron-phonon coupling time of Cu NPs, the ablation area was drastically reduced and the power window for successful sintering was extended by about two times. Simultaneously, the heat-affected zone can be reduced by 66% (area). This new strategy can be adopted for all the SLS processes with fs laser and unlock the power of SLS with fs lasers for future applications.
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Subadditive femtosecond laser-induced electron emission from a GaAs tip
Multiphoton emission of electrons has been observed from sharp tips of heavily p-doped GaAs caused by laser pulses with, nominally, 800-nm wavelength, 1-nJ/pulse energy, and 90-fs duration. The emission is mostly due to four-photon processes, with some contribution from three-photon absorption as well. When the electron emission current due to two pulses separated by delay 200 fs << τ << 1 ns is integrated over all electron energies, it is less than that observed for the sum of the emission from the two individual pulses. This subadditive behavior is consistent with a fast electron emission process, i.e., one in which the electron emission occurs over a time comparable to the laser pulse width. The subadditivity results from Pauli blocking of electron emission by the second pulse due to a population increase of the GaAs conduction band caused by the first pulse. Such subadditive photoemission is a sensitive probe of excited-carrier dynamics. We employ the use of an excited-level population model to characterize the photon absorption process and give us a clearer understanding of the electron dynamics in GaAs associated with multiphoton electron emission. Possible applications of this subadditivity effect to control photoemitted electron spin are discussed.
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- Award ID(s):
- 2207697
- PAR ID:
- 10534779
- Publisher / Repository:
- american physical society
- Date Published:
- Journal Name:
- Physical review B
- Volume:
- 109
- ISSN:
- 2469-9969
- Page Range / eLocation ID:
- 184101
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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