Description

Filter

A THz bandpass filter with (hereinafter, a filter) is intended for spectral filtering of electromagnetic radiation in the terahertz band of the electromagnetic spectrum. The filter provides high transmission of wavelengths in a given spectral interval and effectively blocks the transmission outside it. Such a filter can be used in quasi-optical systems of spectral analysis to measure or monitor emission from broadband terahertz sources; to remove or select frequency harmonics in radiation spectra; for suppression of unwanted spectral components in the incoming radiation which may saturate THz detectors, etc.

Each filter is accomplished as a set of specially designed perforated metal foils (1) (meshes) mounted on circular ring frames inside a cylindrical metal housing (2) with an outer (free) diameter of Æ69 mm (Fig. 1). The metal housing (2) is covered with a protective black paint. To prevent dust from getting inside the filter, its optical (open) aperture of Æ52 mm is protected from both sides by thin THz-transparent polymeric  films (3). A label (4) indicating the filter model (see Table 1 in paragraph 2) is stuck on the filter housing (2).

Fig. 1. Structure (a) and appearance (b) of a THz filter.

Caution:

The filter is a fragile device. Please, do not drop it!

Also, since the protective films (3) are very thin, never touch them with fingers or hard objects! If you revealed dust particles on the surface of the protective films and wish to remove them, please use a soft brush for that (a squirrel brush is preferable).

Filter holder

To mount the filter on an optical table or optical rails, the filter is supplied with a supplementary metal holder (Fig. 2). The holder has a blind M5 threaded hole at the bottom, which allows the filter to be fixed on an optical post. The holder’s surface is covered with a protective black paint.

Fig. 2. Photos of the filter holder.

Due to presence of ledges on the holder’s faces, the filter can be safely fixed in the holder when using (Fig. 3).

Fig. 3. Photos of the filter before (left) and after (right) its mounting in the holder.

Plastic case

To safely store and ship the filters and holders, plastic cases are included in the delivery set (Fig. 4). The standard case is equipped with a handle for carrying and has the overall dimensions of 188´174´58 mm. The case also has an air valve to equalize internal and external pressure. Inside the case, there is an insert made of foamed metallized polyethylene with the nests cut out for one filter and one holder (Fig. 5).

Fig. 4. Closed plastic case used for storage and transportation.

Fig. 5. Open plastic cases without (left) and with (right) the filter and the holder inside.

Technical parameters

The filters included in the current delivery set meet the following technical requirements:

1)    The set include three THz bandpass filters with central frequencies n_max and relative bandwidth Dn/n_max (FWHM) listed in Table 1:

Table 1

Filter no.	Model no.	nmax, THz	Dn/nmax, %	Quantity, pcs.
1	BPF-080-BW20	0.80	20	1
2	BPF-100-BW18	1.0	18	1
3	BPF-200-BW15	2.0	15	1

2)   Peak  at the central frequency: 85% ± 5%;

3)   Allowable deviation for the central frequency: ± 1%;

4)   Allowable deviation for the relative bandwidth: ± 0.5%;

5)   Transmission outside the passpand band: < -40 dB;

6)   Open/free aperture diameter: 52/69 mm;

7)   Each of three abovementioned filters is supplemented with a filter holder specified in paragraph 1.2;

8)     Each filter together with the filter holder is packed in an individual plastic case described in paragraph 1.3.

The THz transmission spectra for the filters in the current delivery set are presented in Fig. 6. The experimental curves (red lines) are obtained with a time-domain spectrometer (TDS) operating in the range of 0.1-2.6 THz.

Fig. 6. THz transmission spectra for the filters in the current delivery set.

Storage and shipment

Using plastic cases described in paragraph 1.3 ensure safe storage and transportation of filters and holders. Inside each case, there is an insert made of foamed metallized polyethylene with nests cut out for the filter and the holder. To avoid damage to the filter, please avoid strong

mechanical shocks and throws of the case when the filter is inside.

When loading and unloading the cargo, observe the requirements and safety measures in force at the respective kind of transport.

The manufacturer is not responsible for any product defects and breakdowns caused by violation of the storage and transportation rules.