The Stanford Research Systems SR542 Precision Optical Chopper modulates light beams with high frequency stability and low phase jitter for demanding spectroscopy, interferometry, and optical sensing applications. Built around a slotless brushless DC motor and precision photo-etched chopper blades, the SR542 delivers repeatable performance across a wide operating range with user-programmable harmonic and sub-harmonic control. Its analog current amplifier eliminates high-frequency EMI while six rear-panel reference outputs enable synchronization of cascading choppers and external instruments via USB or multiple synchronization sources.
Technical Specifications
• Frequency Range: 0.4 Hz to 20 kHz (blade-dependent)
• Frequency Accuracy: 20 ppm (0.002%)
• Phase Resolution: 0.01°
• Phase Jitter: 0.4° to 1.1° rms depending on operating frequency
• Chopper Blades: Precision photo-etched blackened stainless steel; 4-inch outer diameter, 0.010-inch thickness
• Blade Options: Single frequency, dual frequency, and variable duty factor designs
• Motor: Slotless brushless DC motor with low mechanical vibration
• Synchronization Sources: External frequency reference (sine or TTL/CMOS), internal crystal oscillator, VCO input (0 to +10 VDC), AC line (50 Hz to 60 Hz)
• Frequency Control: User-programmable multiplier/divider for harmonic, sub-harmonic, or fractional harmonic operation
• Phase Control: 0.01° resolution with adjustable offset; zero-phase reference capability
• Shutter Mode: Operates as optical shutter via phase setting at 0 Hz internal frequency
– Key Features
• Analog 3-phase sinusoidal motor drive eliminates PWM-related EMI
• Brushless motor design minimizes wear and extends operating life
• Removable shroud prevents accidental contact with rotating head
• Flexible mounting to 1-inch optical breadboard (2-inch slot spacing) or 0.5-inch optical post
• Six rear-panel BNC reference outputs for instrument cascading and external triggering
– Interfaces
• USB computer control with 115,200 baud serial port emulation
• Two BNC inputs; six BNC outputs
• Direct integration with multi-instrument optical systems
