Friday, March 11, 2016

New THz Blog-Taiwan THz Optics Lab

My Note: I just came across this new THz blog. The authors name is not mentioned.

Terahertz Optics is a branch of optics and photonics, studying electromagnetic radiation with a wavelength range of 0.1 ~ 1mm (0.3 ~ 3THz), corresponding a frequency of approximately one terahertz (a trillion hertz). Terahertz (THz) radiation is attracting considerable interest owing to potential applications in imaging and spectroscopy for medical diagnostics and biology, high bandwidth communication, security and defense, and non-destructive evaluation.
THz Optics Lab in NCKU develops the THz sensing methods based on a femtosecond pulse. Several methodologies are first expanded at 2008 and grounded as the categories of :
(1) Plastic Wire THz-Fiber
(2) Dielectric Pipe THz-Fiber
(3) Thin-film-based THz-integrated System
(4) THz Spoof Surface Plasmon Polaritons (THz-SSPPs) based on Metal Rod Array(MRA)
(5) Functional THz Meta-devices

Based on the created bases, the group will analyze molecular binding, molecular polarity, chemical and physical reactions. The developed THz sensing technology is not only different from the analysis of traditional THz spectroscopy but also opens a new field, comparing to the current optical methods of spectroscopy and microscopy. The spectroscopy is well known for the Raman spectroscopy, fluorescence spectroscopy, ultrafast laser spectroscopy, X-ray spectroscopy and infrared ray spectroscopy. THz spectroscopy based on THz electromagnetic radiation possesses considerably low photon energy (1THz~4meV) and belongs to the infrared ray spectroscopy. The optical responses in the well-known spectroscopy show the perturbation results of intra-molecular force (i.e. among the atoms or inside a molecule) using electromagnetic waves in the x-ray, UV, visible lights and infrared-ray spectra. Oppositely, the THz-electromagnetic waves responses the information among the intermolecular force, affiliation, attraction and boundary. The target molecules interacted by the THz-electromagnetic waves can be identified from the different strengths of local or the near-field surrounding the molecule groups(i.e. a minute amounts of molecules) that can be straightforward controlled by the aforementioned bases. 
The Core Technology to Develop:
New concepts of time-domain spectroscopy
3D printing technology for THz-sensors 
System-on-a-chip and lab-on-a-chip for THz-waves
New applications of THz chip sensor

(1) Plastic Wire THz-Fiber: 

   The plastic wires are successfully developed by the THz spectroscopy as one highly directive component, which corresponds to one “ THz fiber” but possesses very small bendable angles without any flexibility within one foot. The feature requests high precision criteria in spatial of a time-domain spectroscopy, grounded on a femtosecond (fs) pulsed laser.    


1. Tunable and strong evanescent field around the plastic wire in spatial and frequency domains.
2. Resolution to identify different refractive index: 0.01 
3. Detectable sample morphology: liquid and solid particles.

1. Optics Express 17, 20675-20683 (2009).
2. Applied Physics Letters 96, 051105 (2010)

(2) Dielectric Pipe THz-Fiber
            The effect of waveguide resonance along a dielectric pipe is successfully developed by a broadband THz spectroscopy. The pipe fibers are well accepted as one channels with multiple functions of a molecular reaction chamber, a waveguide, and a resonator in a THz-photonic system. From the strong and distinct THz-field resonance, the refractive-index and thickness variations of chemical/physical reactions inside the pipe chamber can be observed without analyzing the phase of electromagnetic waves. 


Detectable sample morphology and sensitivity: solid particles (22.2GHz/RIU & 0.01-
Dn), membranes (l/225, 1.22 pico-mole/mm2) and vapors (1.6nano-mole/mm3)

1. Optics Express 18309-322 (2010).
2. Optics Express 18, 19353-19360 (2010).
3. Optics Express 19, 162-167 (2011).
4. Optics Express 20, 5858-5866 (2012).

(3) Thin-film-based THz-integrated System

          Dielectric thin-films are accepted as one simple substrate to guide THz-waves with the advantages of uniform electromagnetic fields, broad bandwidth, low-loss and low-dispersion. Based on the properties, our group successfully develop the concept in subwavelength optics, plasmonic waveguides, and surface-wave sensing in THz-frequency region. 

Tunable confinement of the surface THz-field using a diffraction metal grating structure, ~ l/4.
Directional guidance control by a diffraction metal grating structure.  
Multiple sensing for particle and membrane
Detectable optical path difference : 2.7mm (~l/289) 
- Detectable molecular density : 17.3 nano-mole/mm2 (n=6~8)   

1.Optics Express 21, 6009-6019 (2013). (Selected in Virtual Journal for Biomedical Optics (VJBO), 
   Vol. 8, Iss. 4 (2013))
2.Optics Express 21, 21087-21096 (2013). (Selected in Virtual Journal for Biomedical Optics (VJBO), 
   Vol. 8, Iss. 10 (2013))

(4) THz Spoof Surface Plasmon Polaritons (THz-SSPPs) based on Metal Rod Array(MRA)

              Periodical arrangement of metal rods with a high aspect ratio are successfully demonstrated as one plasmonic metamaterial to deliver THz electromagnetic waves, dependent on the geometric dimensions of each pitch. Such artificial material can be edge coupled to excite THz-SSPPs without any request of high-index medium or certain incident angle to achieve phase-matching criteria. The MRA is first used as one integrated-waveguide substrate in our group to optimize the evanescent surface field to sense nano-thin film and presented for one novel.  

Tunable confinement of the surface THz-field using different period of MRA.
Electromagnetic phase of THz-SSPPs is highly sensitive to the dispersion variation around the
Detectable thin-film thickness: 252 nm, which is equivalent to λ/3968. 

Optics Express 22, 11340-11350 (2014). (Selected in Virtual Journal for Biomedical Optics (VJBO),
Vol. 9, Iss. 7 (2014)) 

(5) Functional THz Meta-devices: 

                   Assembling thin-films is successfully developed as one artificial medium to combine THz-electromagnetic field and analyte molecules. The artificial medium of thin-film stack is considered as one metamaterials to interact the target molecules and enhances the sensitivity of THz-waves beyond the corresponding natural performance. Our group optimize the sensitivity via the thin-film-stacked metamaterial, presenting for one functional THz meta-device in molecular sensing technology. The sensor style realizes the disposable usage with very low cost, comparing to other meta-materials based on the nano-scaled patterns or semiconductor substrates. 

Simple multilayer-stacked microporous polymer membranes are experimentally validated in the
  THz regime for organic vapor sensing under ambient atmosphere and room temperature.
- The hydrophilic porous polymer structure provides a large surface area to adsorb polar vapors, and
  exhibits excellent discrimination in different types of organic vapors based on distinct dipole
- Various concentrations of volatile vapors can also be successfully distinguished by detecting the
  limits of low ppm concentrations.  

Optics Express 23, 2048-2057 (2015). 

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