Broadband THz Sources from Gases to Liquids

Abstract

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.

Plasma-based terahertz wave photonics in gas and liquid phases

“…As one of the most direct approaches, the use of other liquids with lower absorption coefficients can achieve a higher THz electric field and broader THz spectral coverage. For example, the THz electric field emitted from ionized α-pinene is 1.8 times that from ionized liquid water, and its corresponding Fourier transform spectrum is broader than that from ionized liquid water [158] . Similarly, the performance of liquid plasma-based coherent detection can be improved using liquids with lower absorption coefficients as the THz sensor.…”

TMO‐Derived γ‐MnO2 Nanosheets for Harmonic Soliton Molecule Pulses Generation

“…Harmonic mode‐locking technology (HMLT) is essential for generating ultrashort pulses with high repetition frequency. [ 59–62 ]…”

Sensitive carbon monoxide detection based on laser absorption spectroscopy with hollow‐core antiresonant fiber

“…[20][21][22][23][24][25] It has the merits of high sensitivity and high selectivity. [26][27][28][29][30][31][32][33] Among them, tunable diode laser absorption spectroscopy (TDLAS) technology is extensively used in various types of gas detection and offers many advantages such as high sensitivity, low cost, quick response time and noncontact measurement. 34,35 In TDLAS, a photodetector is used to gauge the change in intensity of light.…”

“…Laser absorption spectroscopy based methods are extensively used for trace gas detection 20–25 . It has the merits of high sensitivity and high selectivity 26–33 . Among them, tunable diode laser absorption spectroscopy (TDLAS) technology is extensively used in various types of gas detection and offers many advantages such as high sensitivity, low cost, quick response time and noncontact measurement 34,35 .…”