Stanford SR542 Precision Optical Chopper

The SR542 Precision Optical Chopper provides ultra-stable and flexible optical chopping. The chop frequency is tunable over a wide range, and frequency and phase can be controlled from a variety of input sources including synchronisation to an external reference. The front panel provides an intuitive view of the entire configuration at-a-glance, while remote USB communication permits full control from a remote PC.

Features:

• 0.4 Hz to 20 kHz frequency range
• Flexible synchronisation
• Low phase jitter
• 0.01° phase resolution
• 20 ppm frequency accuracy
• Long-life brushless motor
• USB computer interface

Flexible Configuration

The chopper can be synchronised to a variety of input sources including an external frequency reference (sine or TTL/CMOS), the internal clock (crystal oscillator), the VCO input (0 to +10 VDC), or the AC Line (50 Hz to 60 Hz). Long-term frequency drift is virtually eliminated. Chop rates as low as 0.4 Hz or as high as 20 kHz can be achieved (blade-dependent).

A user-programmable multiplier and divider enable chopping rates at a harmonic, sub-harmonic, or fractional harmonic of the primary frequency.

The user can select the inner slots, outer slots, or the shaft (one-pulse-per-revolution) to be phase-locked to the scaled primary reference. A phase offset is easily adjusted with 0.01° resolution, and a relative phase can be set as a zero-phase reference.

Chopper Head

The chopper head employs a slotless, brushless DC motor (BLDC), which minimises mechanical vibrations and helps keep your optical setup quiet. Furthermore, without the wear-and-tear experienced by the commutator brushes of a DC motor, the operating life of the chopper head is extended.

Precision photo-etched blackened stainless steel chopper blades come in a variety of single and dual frequency designs, plus a variable duty factor design. Tight tolerances for the blade etching ensures low phase jitter of the optically chopped signals.

The chopper head can be mounted to a standard one inch optical breadboard using the slotted base plate (two inch slot spacing) or to a half inch optical post with the included clamping knob.