Date of Award


Degree Name

Doctor of Philosophy


Material Science and Engineering


Chunqiang . Li


Two-photon absorption is a nonlinear optical process where two photons are absorbed by a molecule simultaneously. The probability of this quantum phenomenon is proportional to the quadratic excitation of light intensity. It has many applications in biomedical and materials research, such as two-photon fluorescence microcopy. The first project is to apply two-photon absorption induced bond cleavage in photoreactive materials for engineering 3D tissue scaffolds. The major challenge for growing thick 3D tissues is the lack of vasculature, where nutrients and oxygen can be delivered to the growing cells. Our collaborators have synthesized a novel polypeptide that is composed of 34-mer chains of 5 hexapeptides linked covalently via 4 N-peptidyl-7-nitroindoline moieties. Femtosecond laser pulses are used to break the bonds in these nitroindoline moieties via two-photon absorption. Thus, disintegrating the structure of this polypeptide. Our long-term goal is to develop a novel hydrogel based on this photoreactive polypeptide and use two-photon absorption to fabricate tunnels mimicking vasculature. The second project is to develop an in vivo two-photon flow cytometer based on Airy beams. In vivo flow cytometry is a biomedical technique that can detect circulating cells in vivo. This early diagnosis technique is crucial for early cancer detections and immunological studies. The major challenge for such an optical instrument is the shallow penetration depth due to tissue scattering. Two-photon excitation utilizes near infrared wavelength lasers, which has deeper penetrations than one-photon excitation. Further we implemented non-diffracting laser beams, such as Airy beams, as the excitation source. These non-diffracting beams have long non-diffracting range (Raleigh range) and the unique property of self-healing, i.e. recovering its spatial profile after tissue scattering. Therefore, non-diffracting beams can significantly increase the penetrations depth of light and make flow cytometry feasible for future clinical use.




Received from ProQuest

File Size

80 pages

File Format


Rights Holder

Aurelio Paez