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# Terahertz - Science topic

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Questions related to Terahertz

Dear Colleagues,

It is claimed that terahertz waves have an interesting penetration capacity in dielectrics.

Is there a mathematical method to evaluate this penetrability of a dielectric medium by a terahertz wave?

Thanks and Regards

A BENOUDINA

It is quite challenging to build a telescope of terahertz beam as it is invisible. Can anyone give some suggestions so that the lab life can be easier?

Hi there,

I wish you are doing great.

I would like to know the state-of-the-art terahertz technology for Imaging (0.5 - 6 THz). Do you know, which company is selling the best one in terms of fast scanning of layered materials, THz power, Frequency range, flexibility, portability, resolution, field-of-view, etc.

I appreciate your time and any feedback.

Best regards,

Shyamal

I would like to use the simulations to assess the feasibility of non-destructive testing using the terahertz method for composite materials of various structures.

I found on comsol database one online webinar/workshop where a terahertz metamaterial was modeled and there, input "(px*py/4/2/Z0_const)*E0^2" this equation is used. I need to know why is this used?

I have read a few papers on this topic but the simulation procedure hasn't been mentioned anywhere. Only results have been shown.

I am recently working on terahertz generation using tilted pump front method in LN crystal. I basically followed the setup in Hirori 2011 apl paper but unfortunately I couldn't see any THz although some SHG can be seen. I used 800 nm, 70 fs laser. I think maybe I am wrong somewhere but I dont know. Can anyone share their practical tips please? For example, which part (angle of grating, location of lens etc. ) is most important? Can the scattering light from the crystal tell us any information? How to tell that we have the teraherz? Thank you very much!

Usually the terahertz source used for terahertz communication is a continuous terahertz wave generated by differential frequency, then can terahertz pulses generated by femtosecond laser be used for terahertz communication?

I believe that Terahertz will be used in 6G system. What do you think?

Spectrum is the basis and scarce resource of mobile communication. The growing demand for traffic requires future mobile communication systems to expand available spectrum resources. Terahertz and Visible Light will be two kinds of attractive candidate spectrum. The development and utilization of terahertz spectrum in communication and other fields has been highly valued by countries and regions from Europe, the United States, Japan and other countries. It has also received strong support from the International Telecommunication Union(ITU). Visible light communication technology is a new communication mode developed with the support of high-speed switch by lighting source. It can effectively alleviate the current problem of radio frequency communication bandwidth tension, and provide a new choice for short-distance wireless communication.

Terahertz wave refers to the electromagnetic wave whose spectrum is between 0.1 and 10THz and whose wave length is 30 to 3000 microns. The spectrum is between microwave and far-infrared light, adjacent to millimeter wave in its low band, and adjacent to infrared light in its high band, located in the transition region between Macro electronics and micro-photonics. Terahertz, as a new frequency band between microwave and optical wave, has not been fully developed. Terahertz communication has the advantages of rich spectrum resources and high transmission rate. It is a very advantageous broad band wireless access (Tb/s level communication) technology in future mobile communications.

Basically, a software that helps to fit the terahertz transmission and conductivity data with the Lorentz model or drude model or drude-Lorentz model or any other material-dependent model to get various related parameters. parameters

Are there any programmable metasurfaces available for purchasing? they should be designed for frequencies above 200 GHz, and can modulate the phase or amplitude of the input terahertz wave rapidly.

Millimetere wave (mmWave) channel model is widely known in the literature [1, eq. (7)], [2, eq. (1)]. [3, (55)].

What is the difference between mmWave vs. Terahertz Channel Models? In other words, is there any paper providing the channel model for Terahertz bands (including path loss, path gains, AoD/AoA, etc.)?

[1] A. Koc and T. Le-Ngoc, "Hybrid Millimeter-Wave Massive MIMO Systems with Low CSI Overhead and Few-Bit DACs/ADCs", Accepted in IEEE 92nd Vehicular Technology Conference: VTC2020-Fall , Victoria, BC, Canada, October 2020.

[2] L. Yan, C. Han and J. Yuan, "A Dynamic Array-of-Subarrays Architecture and Hybrid Precoding Algorithms for Terahertz Wireless Communications," in IEEE Journal on Selected Areas in Communications, vol. 38, no. 9, pp. 2041-2056, Sept. 2020

[3] A. Morsali, A. Haghighat and B. Champagne, "Generalized Framework for Hybrid Analog/Digital Signal Processing in Massive and Ultra-Massive-MIMO Systems," in

*IEEE Access*, vol. 8, pp. 100262-100279, 2020I am a communication engineering student and I am interested in doing research in Terahertz generation. So my question is what are the subjects or topics that I do need to have a sound knowledge before going into it?

I want to calculate terahertz spectra for my system but I am confuse about how to do it. The program I am using (crystal17) has two options, one is to perform frequency calculations at gamma point and calculate IR spectra which by default comes from 0 to 4000 cm

^{-1 }. Another option is to do phonon dispersion calculations (http://tutorials.crystalsolutions.eu/tutorial.html?td=dispersion&tf=dispersion-ht) which generate supercell and perform calculations on it. I am confused about if the treahartz spectra will be the regular IR spectra taken between 0 to 100 cm^{-1}or it should be calculated from the phonon dispersion calculations.Plz tell all possible antenna type which can be used for Terahertz

A preliminary study of device orientation and its effect has been investigated in the following paper.

Laplace model for device orientation has been validated through experimental measurements.

Hello friends

Do you know an easy method (e.g. software, open-source code, etc.) for the extraction of materials properties (e.g. permittivity and loss) from TDS data?

I am new to this field and have no background in physics.

Hi everyone,

I am working on a project about Terahertz antenna. I fabricated an antenna with CPW-feeding structure, with size of 200 um. The s11 parameters can be obtained by GSG proble+VNA+Thz Module.

However, i have no idea on how to measure the radiation of the antenna since it has to been tested on a wafer probe system, which is not ready to be moved into a Chamber.

It is said that the Total Radiated Power is the the potential parameter that can be measured.

Does anyone could please help on how to setup and calibrate the system for Total Radiated Power for 140-220GHz planar antennas?

Thank you very much in advacne!

Best,

Bin

I am concerned about the energies of EM radiations. Like the visible has an energy in the range of 1eV, UV has an energy of 10 eV. So when we shine the EM on a semiconductor, how does it affect the charge carrier concentration of it.

- I'm new in the field, working on characterization for a model of air , cotton , air in the terahertz band.
- I need to calculate the Permittivity of the cotton in the range from 0.5- 1.5 THZ needed to calculate the total pathloss.

A highly structured semiconductor material with a conductivity type is available. What material can be modified to obtain a terahertz radiation source?

Why is only femto second laser used. How is it related to terahertz generation?

Can you give me an idea regarding THz wave propagation in human body, any model or any experimental measurements to get some sort of ideas.

I am simulating a THz structure with discrete port in current mode ( not S-parameter or Voltage mode), now my problem is how to obtain S-parameter and efficiency with that?

here is not in 1D-results S-parameters and efficiency results?

regards

In 0.1 - 10 THz regime, how to reduce the path loss?, what are issues associated with path loss?

is there any reference to display the development of methods?

I just wants to measure the protein sample using THz Spectroscopy. Can anybody suggest me what concentration is appropriate??

I am developing a CCTV Terahertz patent - but I have my own use cases - please read my suggestions - mainly in German - please use a translator.

Hi

I want to enter the conductivity of superconductor in cst but according to this paper, it is complex and depend on the angular frequency of incident terahertz wave. how can I do it?

thanks for your help

Hello,

Could anyone suggest a paper giving the far infra-red or terahertz complex refractive index of graphene?

Thank you!

Dear Respectful Researchers,

With 5G still under going (well and fast), 6G falls into the radars of quite a bunch of pioneers in the telecommunications and related areas. To be honest, It may be

**not too early**to "worry about" it, since around every 10 years there comes a newer generation of wireless communication.From the frequency domain, 5G wireless system designs are already moving to millimeter wave (mmWave) bands as high as 100 GHz. Will Terahertz (>300 GHz) be the next domain

**6G will conquer**in terms of the spectrum. However, what type of challenges would be using THz for mobile communications ? Since THz are more close to behave as "optical" than mmWave, how fast/soon could we expect it to be used for real-life communication, based on the R&D progress of current state-of-the-art designs ?Moreover, what else significant technological evolutions or revolutions do we

**expect/predict**to deeply impact the future 6G and form it ?**AI, LiFi, Quantum Computing**, etc. And, what kinda of fancy applications scenarios could you think of/expect/predict ? (E.g. holographic gaming, super deep immersive video, etc. )Dear researchers, thanks for your discussion and inputs.

How spp waves are generated in transmitting type of graphene based patch antenna at terahertz frequency?

There are currently two mainstream theories when describing the generation mechanism of terahertz waves. One is an ionized photocurrent model, and the other is a four-wave mixing model. The four-wave mixing model is designed to the third-order nonlinear process in the filament. However, third-order nonlinear processes have encountered difficulties in describing the strength of terahertz waves. It has been reported in the literature that higher order nonlinear effects are more effective than third order nonlinear effects. We know that higher order nonlinearities require higher light intensity. My confusion is that the four-wave mixing model is suitable for laser energy with low laser energy, which corresponds to the pulsed laser energy when the plasma has not yet formed. Then why is the higher-order nonlinear effect for such low energy more important than the third-order nonlinear effect? My confusion stems from the b diagram in Figure 12 in the following article.

One sentence from reference say: “ Unlike nonlinear crystals, a lack of phonon modes in plasma prevents THz absorption, resulting in broadband THz radiation with no spectral gap”。 Can we understand that this plasma does not absorb terahertz waves? But， we also often see literature mentioning the absorption of terahertz waves by plasma. So what is the relationship between the nature of the plasma and the absorption of terahertz waves?

The femtosecond laser can form a plasma in the air, and broadband terahertz radiation is formed in the plasma due to the oscillation of positive and negative charges. We know that there are two main frequencies involved. One is the oscillation frequency of the plasma and the other is the peak frequency of the terahertz spectrum. The usual study considers the peak frequency of terahertz to be the intrinsic oscillation frequency of the plasma. Is the oscillation frequency of the plasma and the peak frequency of the terahertz

**really equal**? What are the**main factors determining**the peak**frequency of the terahertz spectrum**?Terahertz range can work with massive MIMO or NOMA??

Terahertz range of frequencies is the future range of mobile communications what are its pros and cons??

I was wondering if LT-GaAs or other III-V materials such as InGaAs/InAlAs that are grown in MBE for Terahertz application can be grown in MOCVD ?

What are the differences? Pros and cons of each method?

Has any one tried growing III-V materials in MOCVD for terahertz application?

Hey, I am new to COMSOL and I am trying to simulate terahertz antenna. For the same, I want to excite the port via femto-pulse. Can anyone suggest me how do i provide local femto-excitation e.g., near anode or cathode. I am working on wave optics module and looking the radiation pattern in far-field.

I have used a QMC ltd. manufactured liquid Helium cooled bolometer, model no. QGeB/2 for Terahertz detection from two color laser produced plasma source. The Terahertz radiation we get is of 1-2 picosecond duration at a repetition of 10 Hz and generates a 6-8 volt signal at 40 dB setting of the bolometer. I am referring the following attached document, taken from the thesis of J van Tilborg (http://alexandria.tue.nl/extra2/200611221.pdf) for calibrating the results for our case. To use the equation (A.6), the values of S (Bolometer voltage responsivity, V/W), η (efficiency of the radiation absorption by the bolometer) and τ (response time of bolometer, given by C/(G-I02 dR/dT), where C is the heat capacity of Germanium and G is the thermal conductance of metallic layer) are required. Correct knowledge of these parameters will only allow me to implement the technique. Voltage responsivity is given in the manual as 16.5 kV/W. η, I suppose is the same as β they have used to calculate the incident power Pdet in chapter 6, page no. 27. The temperature in lab was maintained at 23 °C and humidity was maintained in a range of 60-70% throughout the experiment. I have mailed the QMC people for parameters. Has anyone used this bolometer for similar purpose?

How might I calibrate the energy of picosecond long Terahertz pulses while using a continuous wave Germanium detector based bolometer?

If some other calibration technique is possible, kindly guide me!

Hi, I am working with Terahertz signals, generally reference and sample, both collected in time domain. When I FFT, I will get a range of frequencies up to 12THz. However, most of the time, above 3.5THz, the FFT signal will be all noise, but sometimes noise can come in at a lower frequency. And given my understanding that the equipment operating range is from 0.1THz - 3.5Thz, and this can vary according to the subject of study, can I ask if there is a way to determine the actual range of Terahertz frequency which can give useful information about signal by making use of FFT information?

I am trying to find the refractive index (n) and extinction coefficient(k) of the complex refractive index of my sample- a fish. The data are collected in time domain via time domain Terahertz reflection spectroscopy. The data are then FFT and n and k are obtained through further calculation. However, the problem is I get positive and negative extinction coefficient over a range of frequencies for my sample (k). What does this mean? Is there any way to rectify this problem?

Any help is deeply appreciated. Thank you!

I am looking for the surface conductivity of graphene in THz range. if chemical potential is 1eV. If you suggest any paper to me then that will be okay.

As i am working on terahertz antennas ,i need to use graphene as a conducting material so that i want to know the parameters of graphene conductivity,permittivity,permeability etc.

Because i do not how to fabricate the protein or biological sample without water to detect under terahertz time domain spectroscopy (TDS) setup like the thin films fabrication processing.

Thanks a lot!!!!!

Hello,

I would like to calculate the refractive index from Terahertz measurement. I'm aware of the established equation to do so from the literature, whish is: 1 + [phi*c/(2*pi*f*d)] where phi is the phase between the sample and the reference signals.

So my question is how to calculate phi? is it just the difference between the peaks of the material pulse and the reference pulse? in that case, it doesn't depend on the frequency which doesn't make sense to me,,

Would someone help me with this,,

thanks all

Please show me some ways of improving the resolution of the terahertz imaging system

For example many reports are available with thickness dependent terahertz generation. Organic single crystals exhibits higher THz efficiency at particular thickness. Could you please explain the reason for thickness dependent THz efficiency?

Hello I would like to simulate that but I don't know to use which of the physics and order of simulation? I had simulated a lot of antenna with comsol but for THz region really I'm beginner in it. Does anyone simulate the terahertz antenna in comsol? Regards,

Hi, Folk!

I would like to measure sample in low-temperature (several 10 Kelvins) using THz TDS. Could anybody suggest a commercially available thermostat for that? A smaller one is better, as there is not large space (30 cm) between two antennas.

Thanks a lot!

We have the refractive index of organic crystal OH1, measured by THz-TDS.

But it seems there is no formula which can describe the refractive index of OH1. I have read a paper 'Terahertz source at 9.4 THz based on a dual-wavelength infrared laser andquasi-phase matching in organic crystals OH1'. It says a formula can fit the measurement well by Lorentz 8-oscillator mode.

So I am looking for the formula fitted by Lorentz 8-oscillator mode. Is there anyone who know the formula or the other formula which can also fit the measurement of refractive index of OH1 in the terahertz range. Thank you so much

Dear all,

Where can I find the complex refractive index of Ge and Te in Terahertz (THZ) region like (0.1 to 2.5 THZ)?

Thanks.

I want to design a various focus liquid lens for terahertz driven by electrode, can you give me some advice or recommend some papers? Thank you

Hello,

Could you tell me how can I calculate frequency dependent dielectric matrix in terahertz regime for molecule.

I have created a super-cell with vacuum layers.

Any ideas?

I have found piezoelectric resonance peaks for my sample so in further I have to take terahertz characterization.

In THz frequencies we use quasi-static capacitance for calculation of output power,

what explanation has the calculation of quasi-static capacitance in high frequencies (terahertz freq.)???

As we all know, the laser pulse duration is in fs. But the terahertz is happend in ps. Does the terahertz wave come within the time scale of fs when the laser is on?

In THz antennas, an AuGe alloy and a layer of Ti/Au (Titanium/Gold) are employed as the electrode material, what is the AuGe and what does it do in antenna performance?

I read an article about a terahertz antenna with a Interdigitated structure (figure attached), and I have a question about the structure,

what the 2nd Au layer does on the top of the whole structure?(main question)

and why SiO2 layer has coated the interdigitated structure?

the link of the main article attached.

What is the value of epsilon(infinity) of Aluminium in terahertz regime?

I am studying Terahertz Time Domain Spectroscopy for Ph.D work.

What is the most effective and best method for THz generation?

I am setting up a CW THz system and have put together both transmission as well as reflection mode setups. Although the maximum photocurrent I am getting for the transmission mode is around 30 nA at 0.1 THz, the maximum I can get for the reflection mode is around 15 nA at 0.1 THz.

Do I need to work more to align the system or this is as much as I can get in a reflection mode.

And what are the components you suggest to work on to boost the SNR in table top systems (generation, pump stability, electric noise immunity, electro-optical sampling vs antenna etc.)?

I have to perform THz time domain spectroscopy measurements in transmission geometry on biological sample (cell cultures). Can anyone suggest a material for the sample holder that does not absorb too much of the THz signal?