ZYGO 4205

Model Series

ZYGO 4000 Series Laser Interferometers

Related models in the series include:

• ZYGO 4200 — Base dual-frequency interferometer
• ZYGO 4205 — Enhanced precision configuration with extended range optics
• ZYGO 4500 — Multi-axis simultaneous measurement system
• ZYGO 7500 — Ultra-high-stability reference interferometer

Technical Specifications

Functional Features

• Dual-frequency laser operation — generates two orthogonally polarized frequencies separated by approximately 1.5 MHz to 2.0 MHz, enabling direction-sensitive displacement measurement without ambiguity
• Picometer-level resolution — resolves displacements down to 0.001 nm through phase-counting electronics
• Quadrature A/B output signals — provides both direction and magnitude information for real-time position tracking
• Air refractive index compensation input — accepts external environmental sensor data (temperature, pressure, humidity, CO₂) for refractive index correction per Edlén equation
• Laser frequency stabilization — active frequency lock to an internal iodine absorption reference or Zeeman splitting reference, ensuring long-term drift below 0.1 ppm per hour
• NIST-traceable calibration — factory-calibrated against national metrology standards with certificate of calibration included

Material Composition

Structural Characteristics

• Optical layout: Heterodyne Michelson interferometer configuration with internal reference arm and external measurement arm
• Internal reference arm length: Fixed path, thermally isolated from external environment
• Measurement arm output: Single collimated beam exit aperture with integrated beam steering optics
• Vibration isolation: Internal optical bench mounted on passive elastomer dampers
• Thermal management: Active temperature control of laser tube and optical bench maintaining ±0.01°C stability
• Form factor: Benchtop instrument with integrated handle for laboratory transport
• Mounting provisions: Four threaded mounting holes (M6) on baseplate for optical table attachment

Working Principle

1. The dual-frequency HeNe laser emits two orthogonal polarization modes at slightly different frequencies (f₁ and f₂), separated by the Zeeman splitting frequency of approximately 1.5 MHz to 2.0 MHz
2. The beam is split by an internal polarizing beam splitter into a reference arm (fixed path) and a measurement arm (directed to the target retroreflector or mirror)
3. The measurement beam reflects off the target and returns to the interferometer, where it recombines with the reference beam
4. The recombined beam produces a beat frequency signal at the detector equal to the difference between f₁ and f₂, which is Doppler-shifted by the target’s velocity
5. The phase change of the beat signal is counted electronically — each full 360° phase cycle corresponds to a displacement of λ/2 = 316.4 nm
6. Sub-fringe interpolation electronics resolve displacement to 1 pm (0.001 nm) by measuring the fractional phase within each fringe
7. The quadrature A/B signals encode both the integer fringe count and the fractional phase, providing unambiguous direction and magnitude
8. Environmental compensation is applied in real time using measured air temperature, pressure, humidity, and CO₂ concentration to correct the effective wavelength via the Edlén equation

Performance Parameters

Advantages and Highlights

• Picometer resolution — the highest resolution available in a commercial laser interferometer, enabling sub-angstrom measurement capability
• Dual-frequency operation — inherently direction-sensitive, eliminating counting errors from vibration or air turbulence
• Zerodur optical bench — near-zero thermal expansion ensures measurement stability independent of ambient temperature fluctuations
• NIST-traceable calibration — every unit ships with a calibration certificate traceable to the National Institute of Standards and Technology (NIST)
• Environmental compensation ready — direct input for temperature, pressure, humidity, and CO₂ ensures accuracy in non-laboratory environments
• 20,000+ hour laser life — exceptional source longevity reduces total cost of ownership
• Compact benchtop form factor — fits on standard optical tables, no cleanroom required for operation
• Industry-standard output signals — quadrature A/B TTL signals compatible with all major CNC controllers, data acquisition systems, and motion controllers

Applicable Industries

Installation Requirements

• Install on a vibration-isolated optical table with surface flatness better than λ/10 (63 nm) over 300 mm
• Maintain ambient temperature within +18°C to +25°C for optimal performance
• Ensure no direct airflow across the measurement beam path (air currents cause refractive index variations)
• Mount using the four M6 threaded holes on the baseplate — do not clamp the optical housing directly
• Connect environmental sensors (temperature, pressure, humidity) to the DB-25 input for full accuracy
• Connect quadrature A/B outputs via 50 Ω terminated BNC cables to the target controller or counter
• Allow a minimum 15-minute warm-up period before taking measurements
• Perform a zero-path calibration after installation using the built-in alignment procedure

Usage Precautions

• Do not look directly into the laser beam — even at 0.5 mW, the HeNe laser at 632.8 nm is a Class 2 laser and direct eye exposure is hazardous
• Do not touch optical surfaces — finger oils and contamination degrade fringe contrast and measurement accuracy
• Do not operate outside the specified temperature range — thermal drift exceeds specification below +10°C or above +35°C
• Do not expose to strong magnetic fields — the Zeeman-stabilized laser frequency is sensitive to external magnetic fields exceeding 5 gauss
• Do not disconnect the environmental sensor input during measurement — uncorrected air refractive index introduces errors up to 1 ppm per °C
• Do not exceed maximum beam velocity of 5 m/s — fringe counting electronics lose lock above this speed
• Replace laser tube only with ZYGO-certified replacement — non-original tubes void calibration certificate
• Clean optical windows monthly using lens tissue and optical-grade isopropyl alcohol (≥99.9% purity)
• Store in a dry, dust-free environment when not in use — cover all optical apertures with protective caps
• Recalibrate annually or after any physical shock, transport, or laser tube replacement to maintain NIST traceability

Part Number Decoding

Document Reference

• Manufacturer: ZYGO Corporation, 450 Main Street, Middlefield, CT 06455, USA
• Parent Company: AMETEK, Inc., 1100 Cassatt Road, Berwyn, PA 19312, USA
• Calibration Standard: NIST SRM 2517 (HeNe Laser Wavelength Standard)
• Applicable Standards: ISO 10360, ISO 11553, ASME B89.4.22
• Software Compatibility: ZYGO MetroPro, ZYGO Mx Software, LabVIEW, MATLAB, all major CNC controllers via quadrature input