A. Ayesheshim

Nonlinear ultrafast modulation of the optical absorption of intense few-cycle terahertz pulses in n-doped semiconductors

We use an open-aperture

Terahertz pulse induced intervalley scattering in photoexcited GaAs

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Intense THz pulses cause H2AX phosphorylation and activate DNA damage response in human skin tissue.

scan technique to show how intense few-cycle terahertz pulses can experience a nonlinear bleaching of absorption in an

Intense THz pulses down-regulate genes associated with skin cancer and psoriasis: a new therapeutic avenue?

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Time-Resolved Terahertz Spectroscopy of Free Carrier Nonlinear Dynamics in Semiconductors

-doped semiconductor due to terahertz-electric-field-driven intervalley scattering of electrons in the conduction band. Coherent detection of the transmitted terahertz pulse wave form also allows the nonlinear conductivity dynamics to be followed with subpicosecond time resolution. Both the

Intense picosecond THz pulses alter gene expression in human skin tissue in vivo

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Effect of intense THz pulses on expression of genes associated with skin cancer and inflammatory skin conditions

scan and time-domain results are found to be in agreement with our theoretical analysis.

Using terahertz time-domain spectroscopy to determine the glass transition temperature of heavy oils

Nonlinear transient absorption bleaching of intense few-cycle terahertz (THz) pulses is observed in photoexcited GaAs using opticalpump--THz-probe techniques. A simple model of the electron transport dynamics shows that the observed nonlinear response is due to THz-electric- field-induced intervalley scattering over sub-picosecond time scales as well as an increase in the intravalley scattering rate attributed to carrier heating. Furthermore, the nonlinear nature of the THz pulse transmission at high peak fields leads to a measured terahertz conductivity in the photoexcited GaAs that deviates significantly from the Drude behavior observed at low THz fields, emphasizing the need to explore nonlinear THz pulse interactions with materials in the time domain.

Nonlinear free-carrier velocity induced by intense terahertz pulse in photoexcited semiconductor materials

Recent emergence and growing use of terahertz (THz) radiation for medical imaging and public security screening raise questions on reasonable levels of exposure and health consequences of this form of electromagnetic radiation. In particular, picosecond-duration THz pulses have shown promise for novel diagnostic imaging techniques. However, the effects of THz pulses on human cells and tissues thus far remain largely unknown. We report on the investigation of the biological effects of pulsed THz radiation on artificial human skin tissues. We observe that exposure to intense THz pulses for ten minutes leads to a significant induction of H2AX phosphorylation, indicating that THz pulse irradiation may cause DNA damage in exposed skin tissue. At the same time, we find a THz-pulse-induced increase in the levels of several proteins responsible for cell-cycle regulation and tumor suppression, suggesting that DNA damage repair mechanisms are quickly activated. Furthermore, we find that the cellular response to pulsed THz radiation is significantly different from that induced by exposure to UVA (400 nm).

Terahertz nonlinear spectroscopy of free-carriers in direct bandgap semiconductors

Terahertz (THz) radiation lies between the infrared and microwave regions of the electromagnetic spectrum and is non-ionizing. We show that exposure of artificial human skin tissue to intense, picosecond-duration THz pulses affects expression levels of numerous genes associated with non-melanoma skin cancers, psoriasis and atopic dermatitis. Genes affected by intense THz pulses include nearly half of the epidermal differentiation complex (EDC) members. EDC genes, which are mapped to the chromosomal human region 1q21, encode for proteins that partake in epidermal differentiation and are often overexpressed in conditions such as psoriasis and skin cancer. In nearly all the genes differentially expressed by exposure to intense THz pulses, the induced changes in transcription levels are opposite to disease-related changes. The ability of intense THz pulses to cause concerted favorable changes in the expression of multiple genes implicated in inflammatory skin diseases and skin cancers suggests potential therapeutic applications of intense THz pulses.