Terahertz Lens

For THz beam guiding between the emitter and detector we offer hyperhemispherical and elliptic silicon lenses and aspheric TPX lenses with different diameter and focal length.

1. Silicon Lenses

1.1 STB-HSL-12-7.1 Hyperhemispherical Silicon Lens with diameter 12 mm and height 7.1 mm

Hyperhemispherical silicon lens

• Material: undoped HRFZ-silicon
• Specific resistance: >10 kΩcm
• Refractive index: 3.41
• Diameter: 12 mm ±0.01 mm
• Height (h): 7.1 ±0.01mm
• Distance (d): 7.7 mm
• Surface: polished
• PCA chip thickness (t): 0.6 mm

Terahertz beam

• Collection angle: 73°
• Divergence angle: 17°
• Virtual focus length: 26.5 mm

1.2 STB-CL-20 - Collimating elliptic silicon substrate Lens with 20 mm diameter

Elliptic collimating lens

• Material: undoped HRFZ-silicon
• Specific resistance: >10 kΩcm
• Refractive index: 3.41
• Diameter: 20 mm ±0.01 mm
• Height (h): 13.8 mm ±0.01 mm
• Distance (d): 14.4 mm
• Flat surface: polished
• Elliptic surface: polished
• PCA chip thickness (t): 0.6 mm

Terahertz beam

• collimated with 20 mm diameter
• collection angle: 54.6°

1.3 Focusing elliptic Silicon substrate Lens STB-FSL-D20-f50

20 mm diameter, 50 mm focal length

Elliptic focusing silicon lens

• Material: undoped HRFZ-silicon
• Specific resistance: >10 kΩcm
• Refractive index: 3.4
• Diameter: 20 mm
• Focal length: 50 mm
• Height (h): 14 mm
• Distance (d): 14.6 mm
• Flat surface: polished
• Elliptic surface: polished
• PCA chip thickness (t): 0.6 mm

Terahertz beam

• focal length (f): 50 mm
• Collection angle (α): 52.7°
• Convergence angle (ß): 10°

Airy disc diameter

• at 300 GHz: 3.6 mm
• at 1 THz: 1.1 mm
• at 3 THz: 0.36 mm

2. Special TPX Lenses for PCA

• Using highly transmissive TPX (Polymethylpentene) lenses the THz beam can be shaped.
• One TPX lens can collimate the divergent THz beam coming from a hyperhemispherical substrate lens.
• With a second TPX lens a sharp THz focus can be realized.
• 1" diameter TPX lenses can be mounted easily onto a PCA with hyperhemispherical silicon lens.

2.1 STB-CTL-D25mm mounted collimating TPX lens for PCA with diameter 25 mm

STB-CTL-D25mm is an accessory for photoconductive antennas (PCA) that are mounted on a 25.4 mm diameter Al heat sink and are equipped with our hyperhemispherical silicon substrate lenses. The divergent THz beam of such an antenna is in a first step slightly collected by the hyperhemispherical silicon lens. In a second step the THz beam is collimated by a 1” diameter TPX (Polymethylpentene) lens, which is also transparent in the visible spectral region. This collimated terahertz beam exits the STB-CTL-D25mm with a diameter of 22 mm. The same configuration can be used to measure a collimated THz beam. An additional focusing TPX lens can be mounted in front of the first TPX lens to obtain a focused THz beam with a focal length of 30 mm.

Collimating TPX lens

• Material: TPX (Polymethylpentene)
• Refractive index: 1.45 @ 1 THz
• Absorption coeff. (α): 0.3 cm-1
• Diameter: 25.4 mm
• Thickness: 10.3 mm
• Design focal length: 42 mm
• Back focal length: 35 mm (from flat surface)

Collimated THz beam

• beam diameter: 22,4 mm

Lens Tube

• Outer diameter: 30.5 mm
• Total length: 29.2 mm

Compatible PCAs

The STB-CTL-D25mm can be used as housing for a PCA, which is mounted on a 25.4 mm diameter Al heat sink. The electrical cable needs to point towards the front side (laser or chip side) of the PCA. Further the PCA needs to be equipped with one of our hyperhemispherical silicon substrate lenses.

2.2 STB-CTLF-D25mm mounted collimating TPX lens for fiber coupled PCA with diameter 25 mm

STB-CTLF-25mm is an accessory for fiber coupled photoconductive antennas (STB-FC-PCA) that are mounted on a 25.4 mm diameter Al heat sink and are equipped with our hyperhemispherical silicon substrate lenses. The divergent THz beam of such an antenna is in a first step slightly collected by the hyperhemispherical silicon lens. In a second step the THz beam is collimated by a 1” diameter TPX (Polymethylpentene) lens. This collimated terahertz beam exits the CTLF-D25mm. It has a diameter of 22 mm. The same configuration can be used to measure a collimated THz beam. An additional focusing TPX lens can be mounted in front of the first TPX lens to obtain a focused THz beam with a focal length of 30 mm.

Collimating TPX lens

• Material: TPX (Polymethylpentene)
• Refractive index: 1.45 @ 1 THz
• Absorption coeff. (α): 0.3 cm-1
• Diameter: 25.4 mm
• Thickness: 10.3 mm
• Design focal length: 42 mm
• Back focal length: 30 mm (from flat surface)

Collimated THz beam

• Beam diameter: 22.4 mm

Lens Tube

• Outer diameter: 30.5 mm
• Total length: 54.6 mm

Compatible PCAs

The STB-CTLF-D25mm can be used as housing for a FC-PCA, which is mounted on a 25.4 mm diameter Al heat sink. The electrical cable needs to point towards the front side (laser or chip side) of the PCA. Further the PCA needs to be equipped with one of our hyperhemispherical silicon substrate lenses.

2.3 STB-FTL-f32.5mm mounted focusing TPX lens with focal length 32.5 mm

STB-FTL-f30mm is a mounted TPX (Polymethylpentene) lens. It is used in combination with STB-CTL-D25mm or STB-CTLF-D25mm to focus the terahertz radiation emitted by a photoconductive antenna (PCA). The collimated THz beam of a photoconductive emitter antenna with a collimating TPX lens (STB-CTL-D25mm or STB-CTLF-D25mm) is focused using the mounted TPX lens STB-FTL-f32.5mm. The focal length is 32.5 mm.

Focusing TPX lens

• Material: TPX (Polymethylpentene)
• Refractive index: 1.45 @ 1 THz
• Absorption coeff.: 0.3 cm-1
• Diameter: 25.4 mm
• Thickness: 8.0 mm
• Back focal length: 32.5 mm

Focused THz beam

• Aperture angle: 17.6°

Airy disc diameter

• at 300 GHz 1.9 mm
• at 1 THz 554 μm
• at 3 THz 185 μm

Lens Tube

• Outer diameter: 30.5 mm
• Total length: 16.5 mm

Compatible PCAs

The STB-FTL-f32.5mm can be used with both STB-CTL-D25mm and STB-CTLFD25mm.

3. TPX lenses with 1" and 2" diameter

List of available focusing plano-convex TPX lenses from stock. Other TPX lenses on request.