Model 651-1
Dual Aperture Light Chopper
The model 651-1 uses the standard head. This is a dual port design allowing two optical beams to be modulated simultaneously at different frequencies, f1 and f2. Two reference (sync) outputs are made available at the control unit, corresponding to f1 and f2, for use with signal recovery processing electronics, such as a lock-in amplifier.
Two small blanking plates are provided with the standard head and one of these allows either the top port or the bottom port to be blanked off to reduce the effect of any stray light passing through an unused path. The second plate provides some measure of beam restriction when using large diameter beams on the higher frequency (ａnd therefore smaller aperture) port. The standard head is supplied complete with a flat base plate to allow the unit to be used in a free standing mode on a bench type surface. A special feature of this support allows the head to be used in the horizontal plane for modulating vertical beams. The base plate can be removed and standard optical mounting supports employed instead if preferred.
Model 651-1 Mechanical Dimensions
Model 651-1 Blade Dimensions
| Operation | |||
| Frequency | 10 Hz to 3200 Hz | ||
| outer sector | 100 Hz to 3200 Hz | ||
| inner sector | 10 Hz to 320 Hz | ||
| Control | |||
| manual | Digital push-button | ||
| external | Application of 0.5 V to 10 V sine or squarewave, 50 Hz to 3200 Hz to EXT SYNC BNC connector | ||
| Internal Frequency | |||
| accuracy | ±30 ppm at 25 °C | ||
| stability | ±50 ppm/ °C (range 10 °C to 30 °C) | ||
| Jitter | (measured pk-pk and presented as a % of a full cycle) | ||
| outer sector | |||
| 100 to 200 Hz | blade only: 0.2%; blade + electronics: < 7% | ||
| 200 to 400 Hz | blade only: 0.2%; blade + electronics: < 4% | ||
| 400 to 2500 Hz | blade only: 0.2%; blade + electronics: < 1.5% | ||
| 2500 to 3200 Hz | blade only: 0.2%; blade + electronics: < 2% | ||
| inner sector | |||
| 10 to 20 Hz | blade only: 0.2%; blade + electronics: < 0.7% | ||
| 20 to 40 Hz | blade only: 0.2%; blade + electronics: < 0.4% | ||
| 40 to 250 Hz | blade only: 0.2%; blade + electronics: < 0.2% | ||
| 250 to 320 Hz | blade only: 0.2%; blade + electronics: < 0.3% | ||
| Lock indication | green LED when locked - can be extinguished | ||
| Settling Time | <40 s nominal | ||
| Outputs | |||
| Sync Out 1 | 10 V pk-pk squarewave at outer sector chopping frequency, 50 - 3200 Hz | ||
| Sync Out 2 | 10 V pk-pk squarewave at inner sector chopping frequency, 10 - 320 Hz | ||
| Connectors | BNC | ||
| Impedance | 10 kΩ. Note that although the output voltage is 10 V pk-pk, the high output impedance means that the outputs can be directly connected to the Reference Frequency input of any SIGNAL RECOVERY lock-in amplifier without causing problems. | ||
| Power Requirements | 110 V AC, 50/60 Hz or 220/240 V AC, 50/60 Hz supply. State which voltage is required when ordering | ||
| Dimensions | |||
| Controller | 6.6" wide x 3.1" high x 9.3" deep (168 mm wide x 79 mm high x 236 mm deep) | ||
| Chopper head, overall, inc. base and feet | 4.8" wide x 5.9" high x 2.8" deep (122 mm wide x 150 mm high x 72 mm deep) | ||
| Options | Model 653A 2 m (6'6") extension cable | ||
