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Resonant Optical Chopper

Features and Advantages

  • ONE FIXED FREQUENCY from 10 Hz to 1,000 Hz
  • Aperture up to 10mm
  • Suitable for long life dedicated applications
  • Simple to use
  • Low cost
  • Small size/lightweight
  • Withstands shock and vibration
  • Low power drive electronics
  • Rugged, no wearing parts
  • High reliability, long life
  • High frequency stability
  • High amplitude stability
  • Ultra high vacuum operation1
  • High temperature operation1
  • Operates at cryogenic temperatures1
  • Meets military specifications1
  • Used in aerospace and atmospheric missions1
  • Jitter free operation
  • No radiated electromagnetic interference (EMI)
  • Reference signal available
  • Dark vanes are standard, bright vanes or mirrors are optional1
  • Single vane for alternate beam chopping1
1 Available on special order
  • Description
  • Drawings
  • Documents

Reliable and Versatile Optical Choppers

Optical choppers are widely used in various scientific applications, usually in combination with lock-in amplifiers. Among optical choppers, tuning fork choppers stand out as the most dependable. With an impressive lifespan, they excel even in extreme environments such as high temperatures, ultra-high vacuums, and cryogenic conditions. Their versatility extends to chopping light, plasma, X-rays, and laser beams.

Key Features of Tuning Fork Choppers

  • Cost-Effective and Compact: The CH-10 is cost-effective, compact, and lightweight, making it suitable for a wide range of applications, OEM, built into an instrument or system, and for small, portable and hand-held systems.
  • Long Life: Offering virtually limitless operational life, tuning fork choppers are ideal for dedicated applications, OEM integration, and incorporation into both large instruments and small portable systems.
  • Military Specifications Available: Special orders for tuning fork choppers meeting military specifications are also accommodated.

Operating Principle

Unlike rotating choppers, a tuning fork chopper operates at one fixed frequency. The chopper moves at the natural resonant frequency established by the effective mass of the moving assembly and the spring constant of the tines. Vanes, attached to moving tines, open and close an apperature to modulate a light beam. Balanced operation and high "Q" insure excellent frequency stability, low electrical drive power and low reaction forces. High flexural stiffness provides good resistance to shock and vibration.

Frequency Range and Aperture Size

The chopping frequency is chosen from a specified range, with practical apertures of up to 15mm for frequencies under 100 Hz. If the beam size is a limiting factor, beam focusing is recommended.

The following should serve as guide lines only:
AT REST(Inches)
LENGTH(Inches) WIDTH(Inches)
10-50 2.81 0.88 1.00 0.63 0.37 0.20
60-200 2.69 0.88 1.00 0.63 0.31 0.20
200-400 2.56 0.88 1.00 0.50 0.31 0.20-0.10
400-600 2.40-2.00 0.88 1.00 0.40 0.24 0.10-0.06
600-800 2.00 0.88 1.00 0.40 0.24 0.06-0.04
800-1000 2.00 0.88 1.00 0.40 0.23 0.04-0.03

(Hz) (mm) (Inches) (mm) (Inches)
10-150 5.1 0.20 10.2 0.40
200 4.0 0.16 8.1 0.32
250 3.8 0.15 7.6 0.30
300 3.1 0.12 6.1 0.24
400 2.4 0.10 4.8 0.19
450 2.0 0.08 4.0 0.16
500 1.8 0.07 3.6 0.14
600 1.5 0.06 3.0 0.12
700 1.2 0.05 2.0 0.09
800 1.0 0.04 2.0 0.08
900 0.8 0.03 1.6 0.07
1000 0.6 0.03 1.2 0.05

Flexibility and Options

Standard options include dark or bright vanes. Dark vanes are generally light aborbent and brigth vanes are generally light reflective. Special vane configurations, such as mirrors, lenses, gratings, and custom shapes, are available upon consultation. Additionally, a range of drive electronics with diverse packaging, regulation, and power supply options are offered. Special pricing is extended to OEM applications. The standard operating temperature range is -40°C to +65°C.

Applications and Benefits

  • Aerospace and Atmospheric Research: Tuning fork choppers find extensive use in aerospace and atmospheric research due to their ultra high vacuum, cryogenic, and high-temperature capabilities.
  • Detection and Noise Filtering: In detection applications where optical signals are obscured by noise, a fixed-frequency modulated signal can be isolated from the background using a lock-in amplifier. The detected signal and the reference signal (mixed with the frequency of the tuning fork chopper) cause the frequency of interest to appear as a pure dc output level. All other signals are filtered with the low pass filter. Once noise is removed, proper signal measurements can be obtained.

Drive Electronics Options

  • ED Driver and AGC Driver: Both function as tuning fork oscillators utilizing the chopper as a frequency source. The AGC driver also ensures high amplitude stability (0.005%) and offers both sine wave and TTL reference signals.
  • PLD-1C Driver and PLD-2C Driver: These drivers enable phase locking of tuning fork choppers to external clock signals, allowing for synchronized operation in master/slave configurations.

Ordering Information

TYPE [CH-10]; DUTY CYCLE [%]; VANE [B=bright or D=dark]; FREQUENCY [Hz]
Example: PART NO. CH10-90D-825. This part number specifies the model CH-10 chopper, with 90% duty cycle, dark vanes and an 825 Hz operating frequency.
Special vane configurations, modulating waveforms and shapes are available on special order. Consult factory. Drive electronics with different packages, regulation, and reference signal and power supply options are available. Special pricing for OEM applications.

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