Matters are generally classified within four states: solid, liquid, gas, and plasma. Three of the four states of matter (solid, gas, and plasma) have been used for THz wave generation with short laser pulse excitation for decades, including the recent vigorous development of THz photonics in gases (air plasma). However, the demonstration of THz generation from liquids was conspicuously absent. It is well known that water, the most common liquid, is a strong absorber in the far infrared range. Therefore, liquid water has historically been sworn off as a source for THz radiation. Recently, broadband THz wave generation from a flowing liquid target has been experimentally demonstrated through laser-induced microplasma. The liquid target as the THz source presents unique properties. Specifically, liquids have the comparable material density to that of solids, meaning that laser pulses over a certain area will interact with three orders more molecules than an equivalent cross-section of gases. In contrast with solid targets, the fluidity of liquid allows every laser pulse to interact with a fresh area on the target, meaning that material damage or degradation is not an issue with the high-repetition rate intense laser pulses. These make liquids very promising candidates for the investigation of high-energy-density plasma, as well as the possibility of being the next generation of THz sources.
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Development of a hardened THz energy meter for use on the kilojoule-scale, short-pulse OMEGA EP laser
A highly adaptable and robust terahertz (THz) energy meter is designed and implemented to detect energetic THz pulses from high-intensity (>1018 W/cm2) laser–plasma interactions on the OMEGA EP. THz radiation from the laser driven target is detected by a shielded pyrometer. A second identical pyrometer is used for background subtraction. The detector can be configured to detect THz pulses in the 1 mm to 30 μm (0.3- to 10-THz) range and pulse energies from joules to microjoules via changes in filtration, aperture size, and position. Additional polarization selective filtration can also be used to determine the THz pulse polarization. The design incorporates significant radiation and electromagnetic pulse shielding to survive and operate within the OMEGA EP radiation environment. We describe the design, operational principle, calibration, and testing of the THz energy meter. The pyrometers were calibrated using a benchtop laser and show linear sensitivity to up to 1000 nJ of absorbed energy. The initial results from four OMEGA EP THz experiments detected up to ∼15μJ at the detector, which can correspond to hundreds of mJ depending on THz emission and reflection models.
more » « less- NSF-PAR ID:
- 10440070
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Review of Scientific Instruments
- Volume:
- 93
- Issue:
- 12
- ISSN:
- 0034-6748
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Developing efficient and robust terahertz (THz) sources is of incessant interest in the THz community for their wide applications. With successive effort in past decades, numerous groups have achieved THz wave generation from solids, gases, and plasmas. However, liquid, especially liquid water has never been demonstrated as a THz source. One main reason leading the impediment is that water has strong absorption characteristics in the THz frequency regime. A thin water film under intense laser excitation was introduced as the THz source to mitigate the considerable loss of THz waves from the absorption. Laser-induced plasma formation associated with a ponderomotive force- induced dipole model was proposed to explain the generation process. For the one-color excitation scheme, the water film generates a higher THz electric field than the air does under the identical experimental condition. Unlike the case of air, THz wave generation from liquid water prefers a sub-picosecond (200 – 800 fs) laser pulse rather than a femtosecond pulse (~50 fs). This observation results from the plasma generation process in water. For the two-color excitation scheme, the THz electric field is enhanced by one-order of magnitude in comparison with the one-color case. Meanwhile, coherent control of the THz field is achieved by adjusting the relative phase between the fundamental pulse and the second-harmonic pulse. To eliminate the total internal reflection of THz waves at the water-air interface of a water film, a water line produced by a syringe needle was used to emit THz waves. As expected, more THz radiation can be coupled out and detected. THz wave generation from other liquids were also tested.more » « less
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