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<p>In semiconductors, two-photon absorption (TPA) occurs when two photons (whose combined total energy must be larger than the band gap) are simultaneously absorbed to excite an electron from the valence to the conduction band. For a monochromatic light beam with photon energy smaller than the band gap but greater than half of it, single-photon absorption is negligible, i.e., the semiconductor is transparent. However, TPA begins as the light intensity increases because the transition rate due to TPA has superlinear dependence on light intensity; as a result, the TPA process can become dominant at high intensities. Hg<sub>1−<i>x</i></sub>Cd<sub><i>x</i></sub>Te alloys grown using the molecular beam epitaxy (MBE) technique were investigated for their TPA characteristics. A unique TPA testing system which employs a pump-probe approach was employed. We present measurements of the reduction in the probe beam signal strength when a high-power pump beam is applied, which indicates that TPA is active in the laser wavelength range. TPA-induced photoconduction was also measured.</p>

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Two-Photon Absorption Behavior of HgCdTe Material

  • 期刊论文

  • 发表日期：

    2025年7月5日

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  • Y. Chang,
  • S. Sonde,
  • I. L. Chang,
  • W. Gao,
  • S. Velicu

摘要

In semiconductors, two-photon absorption (TPA) occurs when two photons (whose combined total energy must be larger than the band gap) are simultaneously absorbed to excite an electron from the valence to the conduction band. For a monochromatic light beam with photon energy smaller than the band gap but greater than half of it, single-photon absorption is negligible, i.e., the semiconductor is transparent. However, TPA begins as the light intensity increases because the transition rate due to TPA has superlinear dependence on light intensity; as a result, the TPA process can become dominant at high intensities. Hg1−xCdxTe alloys grown using the molecular beam epitaxy (MBE) technique were investigated for their TPA characteristics. A unique TPA testing system which employs a pump-probe approach was employed. We present measurements of the reduction in the probe beam signal strength when a high-power pump beam is applied, which indicates that TPA is active in the laser wavelength range. TPA-induced photoconduction was also measured.