A compact, low cost, 7 channel polychromator for Thomson scattering measurements
Abstract
A seven channel polychromator, utilizing high performance interference filters, was tested for use in the multi-Nd:YAG laser Thomson scattering system for the DIII-D tokamak. Unique features of this polychromator are the combination of high throughput, easy alignment, flexibility, compact size, and low cost when compared with other alternatives. Light is introduced to the polychromator (f/1.75) via a fiber optic bundle which permits the use of small (3.0 cm dia) optics and leads to a compact design, an important design consideration for multiple polychromator systems. The light is cascaded through a series of different bandpass interference filters and relay lenses which are mounted on two precision parallel rails in such a way that alignment is trivial. The relay lenses are positioned directly in front of the filters so that light reflected from the filter passes through the lens twice. This leads to an efficient, compact design and reduces the angle of incidence (4 deg) and the cone angle of light (4.5 deg) seen by the filter, an important factor for narrowband (3.0 nm) filters. The transmission was optimized for 700 to 1100 nm by using broadband coatings throughout. The output images of each channel (2.3 mm dia) can be directly coupled to large format (3 nm dia) RCA silicon avalanche photodiode detectors, avoiding the losses caused by fiber optic coupling.
- Publication:
-
Presented at the 8th Topical Conference on High-Temperature Plasma Diagnostics
- Pub Date:
- October 1990
- Bibcode:
- 1990htpd.conf....7C
- Keywords:
-
- Electron Energy;
- High Temperature Superconductors;
- Plasma Density;
- Plasma Diagnostics;
- Thomson Scattering;
- Tokamak Devices;
- Yag Lasers;
- Charge Coupled Devices;
- Fiber Optics;
- Low Cost;
- Neodymium Lasers;
- Quantum Efficiency;
- Plasma Physics