A Versatile THz Source from High-Brightness Electron Beams: Generation and Characterization

Round 1

Reviewer 1 Report

This manuscript presents to the method of generation and characterization of THz radiation produced by high brightness electron beams available at the SPARC_LAB test facility.

The topic addressed is interesting that are clearly of broad interest and deserve publication.

However, a revision of the manuscript is needed before it can be accepted for publication.

Herewith a detailed list of comments and suggestions:

(1) There seems to be a misspell or omission in the words used in the text. There are other things you may have overlooked. (lines: 120, 238)
(2) What is the formula for the form factor used to describe Figure 1? It is easier to understand by showing it in the text. (lines 75-76)
(3) Other than the word "Frozen", is there any other expression that is easier to understand? (line 94)
(4) What are the specifications of the "diamond window"? (line 106)
(5) How much humidity is in the air (or in a dry air environment)? (lines 107-108)
(6) What are the specifications of the dry air system? In addition, the range of spaces to be filled with dry air is not shown. (line 109)
(7) The material, thickness and size of the CTR radiator are also important for CTR emission. I think it would be easier to understand if the specifications were included in the paper. (Fig3)
(8) Only "the 5 THz band-pass filter" does not show a model number. (line 166)
(9) The order of appearance of figure numbers in the text is Figure 3->Figure 5->Figure 4 (lines 105-> lines 125 and 130-> line 138)... If you want to use Figure 5 in chapter 2, I think you need to add some other figure or change the structure of the text.
(10) Is this figure 6 of the manuscript is recycled or is the different measurement procedure? It seems to be the same as the figure with the error bars removed from Fig. 3(a) in Reference 11.
(11) Table titles must be filled in at the top of the table. (lines 170-171)
(12) Is the Peak power of Single Bunch ~80 MW in Table 1 the number you have obtained in the discussion in this paper? It differs from Table 2 in Reference 11.
(13) A short paragraph offering "Author Contributions" is required, specifying the individual's contribution.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript provides an overview on how coherent THz pulses are produced in particle accelerators and more specifically, discusses results from SPARC_LAB on the production of THz pulses from single electron bunches and from multi-bunch trails. The paper is well structured and written. I have only minor comments for improvements which are stated below. I recommend the paper for publication in Condensed Matter.

 

-       The abbreviations CDR and CTR need to be explained when appearing first in the text.

-       The figure 1 needs some sentences of explanation/description.

-       The figure 3 shows a non-polarizing Michelson interferometer for auto-correlation measurements. The auto-correlation measurements presented are obviously done with a polarizing Martin-Puplett interferometer (MPI). Is it difficult to change this in the figure?

-       Page 5, first paragraph: This paragraph needs some refinements answering the following questions for the reader. Perhaps some unnecessary statements could be skipped. For what purpose a two-beam interferometer is mentioned and what is it good for? What is the polarization state of the transition radiation (TR) when entering the MPI?  Are linear polarizers and analyzer used at the entrance and exit of the MPI, respectively, or was the initial polarization of TR used as is? What is the different and sum interferogram and how do they relate to the results shown?

-       The experimental information on how the results of figure 6 are obtained have to be implemented in the experimental section (2.3) of the manuscript. This includes information on the detector used and on its calibration for obtaining absolute values as shown in figure 6.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This is an interesting paper presenting results on THz radiation generated by the SPARC photo injector facility.

Due to the potential of electron beam shaping a wide variety of the THz signals can be generated, single-cycle as well as multi-cycle pulses. It would be helpful if the source parameters

Wavelength range

Pulse energy

Pulse repetition rate

for both single-cycle and multi-cycle pulses

would be given. To help the reader in understanding the significance of the source here, it would be good to see some comparison with other linac based sources like the TELBE as well as laser based sources.

How sensitive are the THz beam parameters to typical fluctuations in charge and energy of the linac?

The paper would benefit from adding the above information.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

This manuscript has been greatly improved and is now easy to understand.