Products
We are actively taking measures to improve product quality levels.
Applications
Why Hamamatsu?
Support
Our company
Investors
Japan (EN)
Select your region or country.
Principle | Terahertz (THz) sensors
Development of THz detector using a metasurface
Photomultiplier tubes (PMT) and image intensifiers (I.I.) use a photoelectric surface based on the principle of the photoelectric effect.
However, unlike light waves, THz waves have low photon energy, making it difficult to directly induce a photoelectric effect.
We have therefore developed a metasurface that converts THz waves into electrons. Here, we introduce the concept of a metasurface and the principle of THz wave-to-electron conversion.
What is a metasurface?
A metasurface is an artificially designed surface structure with microstructures that is used in a variety of applied technologies. It is called a metasurface because it is a surface with periodic microstructures (meta) arranged on it.
Hamamatsu Photonics applies this metasurface to THz detection. Therefore, a metasurface here refers to a THz wave-to-electron conversion element.
A metasurface consists of an array of gold antenna patterns on a substrate such as quartz or silicon, and when a THz wave is incident, electrons are emitted according to the principle of field electron emission. These electrons are amplified and output to detect THz waves.
Image of field electron emission
Enlarged image of metasurface microstructure
Principle of field electron emission
THz wave-to-electron conversion uses the principle of field electron emission. Here, we introduce the principle of electron emission with a metasurface and THz wave electric fields, in comparison with the photoelectric conversion used in ordinary photomultiplier tubes.
Field electron emission with metasurfaces is known as a highly non-linear phenomenon that depends on the electric field intensity.
In addition, through research, it has been found that coating with an alkali metal reduces the work function of the antenna metal (gold) surface, enhancing the sensitivity to THz wave electric fields. Taking advantage of this property, Hamamatsu Photonics’ metasurfaces are coated with alkali metals on the surface of the antenna to increase sensitivity.
The antenna design also allows the frequency band in which THz waves resonate with the antenna to be freely designed, making it possible to support a wide range of bands from the sub-THz region to the mid-infrared region.
Field electron emission by a metasurface (THz photomultiplier tube)
Band model of a metasurface
In electron emission using metasurfaces, the electric field of the THz waves is amplified by the antenna and concentrated on the emitter.
A high electric field is concentrated on the emitter. The high electric field generated by the THz waves tilts the vacuum level on the gold antenna surface, causing the electrons at the Fermi level of the gold to tunnel into the vacuum side. This is the phenomenon known as field electron emission.
The electrons emitted by field electron emission move through the vacuum according to the surrounding electric field.
1. THz waves are incident on the antenna and the electric field is concentrated.
2. The high electric field tilts the vacuum level on the gold antenna surface.
3. Electrons at the Fermi level of the gold are tunneled into the vacuum side.
Photoelectric effect by an alkali photocathode (an ordinary photomultiplier tube)
Band model of a photocathode
Semiconductors have an “energy gap,” which is the width of the forbidden band where electrons cannot exist, an “electron affinity,” which is the distance between the conduction band and the vacuum level, and a “work function,” which is the energy difference between the Fermi level and the vacuum level.
When photons are incident on a photocathode, electrons in the valence band absorb the photon energy, are excited, and diffuse to the surface. The diffused electrons exceed the vacuum level and are emitted into the vacuum as photoelectrons.
1. Photons are incident on the photocathode and electrons in the valence band are excited.
2. The excited photoelectrons are diffused to the surface.
3. The photoelectrons that exceed the vacuum level are emitted into the vacuum.
Non-linear output from field electron emission
The principle of field electron emission follows the Fowler-Nordheim relation formula.
Here, a and b are the FN constants, F is the work function, β is the electric field concentration factor, and E is the THz wave electric field intensity. The amount of electron emission is determined by the electric field intensity E of the THz wave. Therefore, a metasurface using this principle may be able to directly measure the THz wave electric field intensity.
In addition, as the relationship between the amount of electron emission and the electric field intensity E is highly non-linear, the amount of electron emission changes significantly with a slight change in the electric field intensity. As shown in the graph, the non-linear response characteristics can be clearly seen when compared with a linear device. This non-linear response characteristic can be applied to micro-change measurements.
Fowler-Nordheim relation formula
Comparison of response characteristics
Related papers
| Classification | Title | Author | Link |
|---|---|---|---|
| Basic principle | Lightwave-Driven Long-Wavelength Photomultipliers | Simon J. Lange, et al., | https://doi.org/10.1002/lpor.202470002 |
| Application | IEEE Transactions on Terahertz Science and Technology | T. O. Buchmann et al., | https://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=5503871 |
| Application | Fourier-transform THz spectroscopy based on electric-field interferometry using THz-PMT | H. Takahashi et al., | https://opg.optica.org/oe/fulltext.cfm?uri=oe-32-7-12774&id=548237 |
- Confirmation
-
It looks like you're in the . If this is not your location, please select the correct region or country below.
You're headed to Hamamatsu Photonics website for JP (English). If you want to view an other country's site, the optimized information will be provided by selecting options below.
In order to use this website comfortably, we use cookies. For cookie details please see our cookie policy.
- Cookie Policy
-
This website or its third-party tools use cookies, which are necessary to its functioning and required to achieve the purposes illustrated in this cookie policy. By closing the cookie warning banner, scrolling the page, clicking a link or continuing to browse otherwise, you agree to the use of cookies.
Hamamatsu uses cookies in order to enhance your experience on our website and ensure that our website functions.
You can visit this page at any time to learn more about cookies, get the most up to date information on how we use cookies and manage your cookie settings. We will not use cookies for any purpose other than the ones stated, but please note that we reserve the right to update our cookies.
1. What are cookies?
For modern websites to work according to visitor’s expectations, they need to collect certain basic information about visitors. To do this, a site will create small text files which are placed on visitor’s devices (computer or mobile) - these files are known as cookies when you access a website. Cookies are used in order to make websites function and work efficiently. Cookies are uniquely assigned to each visitor and can only be read by a web server in the domain that issued the cookie to the visitor. Cookies cannot be used to run programs or deliver viruses to a visitor’s device.
Cookies do various jobs which make the visitor’s experience of the internet much smoother and more interactive. For instance, cookies are used to remember the visitor’s preferences on sites they visit often, to remember language preference and to help navigate between pages more efficiently. Much, though not all, of the data collected is anonymous, though some of it is designed to detect browsing patterns and approximate geographical location to improve the visitor experience.
Certain type of cookies may require the data subject’s consent before storing them on the computer.
2. What are the different types of cookies?
This website uses two types of cookies:
- First party cookies. For our website, the first party cookies are controlled and maintained by Hamamatsu. No other parties have access to these cookies.
- Third party cookies. These cookies are implemented by organizations outside Hamamatsu. We do not have access to the data in these cookies, but we use these cookies to improve the overall website experience.
3. How do we use cookies?
This website uses cookies for following purposes:
- Certain cookies are necessary for our website to function. These are strictly necessary cookies and are required to enable website access, support navigation or provide relevant content. These cookies direct you to the correct region or country, and support security and ecommerce. Strictly necessary cookies also enforce your privacy preferences. Without these strictly necessary cookies, much of our website will not function.
- Analytics cookies are used to track website usage. This data enables us to improve our website usability, performance and website administration. In our analytics cookies, we do not store any personal identifying information.
- Functionality cookies. These are used to recognize you when you return to our website. This enables us to personalize our content for you, greet you by name and remember your preferences (for example, your choice of language or region).
- These cookies record your visit to our website, the pages you have visited and the links you have followed. We will use this information to make our website and the advertising displayed on it more relevant to your interests. We may also share this information with third parties for this purpose.
Cookies help us help you. Through the use of cookies, we learn what is important to our visitors and we develop and enhance website content and functionality to support your experience. Much of our website can be accessed if cookies are disabled, however certain website functions may not work. And, we believe your current and future visits will be enhanced if cookies are enabled.
4. Which cookies do we use?
There are two ways to manage cookie preferences.
- You can set your cookie preferences on your device or in your browser.
- You can set your cookie preferences at the website level.
If you don’t want to receive cookies, you can modify your browser so that it notifies you when cookies are sent to it or you can refuse cookies altogether. You can also delete cookies that have already been set.
If you wish to restrict or block web browser cookies which are set on your device then you can do this through your browser settings; the Help function within your browser should tell you how. Alternatively, you may wish to visit www.aboutcookies.org, which contains comprehensive information on how to do this on a wide variety of desktop browsers.
5. What are Internet tags and how do we use them with cookies?
Occasionally, we may use internet tags (also known as action tags, single-pixel GIFs, clear GIFs, invisible GIFs and 1-by-1 GIFs) at this site and may deploy these tags/cookies through a third-party advertising partner or a web analytical service partner which may be located and store the respective information (including your IP-address) in a foreign country. These tags/cookies are placed on both online advertisements that bring users to this site and on different pages of this site. We use this technology to measure the visitors' responses to our sites and the effectiveness of our advertising campaigns (including how many times a page is opened and which information is consulted) as well as to evaluate your use of this website. The third-party partner or the web analytical service partner may be able to collect data about visitors to our and other sites because of these internet tags/cookies, may compose reports regarding the website’s activity for us and may provide further services which are related to the use of the website and the internet. They may provide such information to other parties if there is a legal requirement that they do so, or if they hire the other parties to process information on their behalf.
If you would like more information about web tags and cookies associated with on-line advertising or to opt-out of third-party collection of this information, please visit the Network Advertising Initiative website http://www.networkadvertising.org.
6. Analytics and Advertisement Cookies
We use third-party cookies (such as Google Analytics) to track visitors on our website, to get reports about how visitors use the website and to inform, optimize and serve ads based on someone's past visits to our website.
You may opt-out of Google Analytics cookies by the websites provided by Google:
https://tools.google.com/dlpage/gaoptout?hl=en
As provided in this Privacy Policy (Article 5), you can learn more about opt-out cookies by the website provided by Network Advertising Initiative:
http://www.networkadvertising.org
We inform you that in such case you will not be able to wholly use all functions of our website.
Close