Wavelength Meters Information

wavelength meters specification guideWavelength meters are interferometers used to measure wavelengths of laser beams. The devices are mounted on benches or desktops. They generate numerical values identifying pulsed and continuous wave lasers. Wavelength meters deliver reliable monitoring of tunable and diode lasers. They enable calculations of improved validity compared with spectrometers or grating monochromators. These measurements range from 0.01 nm to hundredths of a picometer. The components monitor wavelengths attributable to tunable lasers or lasers experiencing wavelength drift without the necessity of complicated long-path methods applied with spectrometers.

 

Standard wavelength meters consist of a photosensor, thermostat, photo amplifiers, and interferometers. Select models are static and feature no moving parts. The majority of the meters include software and an interface designed for controlling the process and analyzing data. The tools determine wavelength resolution indirectly through wave frequency units. Wavelength meters cover a broad spectrum of applications, including tasks demanding superior accuracy in laser wavelength information such as industrial spectroscopy and optical communications manufacturing.

 

Types

 

Wavelength meters rely on interferometers to obtain a precise computation. Michelson or Fizeau interferometers present the most popular choices. Meters of these types have the following characteristics:

 

Michelson interferometer-based: When testing an optical source, the units supply light into a Michelson interferometer. At the same time, the length of an interferometer arm is subjected to scanning over a particular range. The output power period is logged by the photodetector against changes in arm length. This reflects the wavelength.

 

A microprocessor controls the activity and executes data analysis.

 

Multiple errors affect measurement precision when using Michelson-based devices:

 

  • Changes or flaws in beam profile present a negative effect. As a result, input light is filtered spatially prior to entering the interferometer. Accomplishing this via a single-mode fiber is ideal. A type of mode cleaner, comprising a pinhole placed between two separate lenses, is used for spatially multimode input light.
  • Drifts in length and scanning device imperfections run the risk of introducing errors into the process. Eliminating these inaccuracies is possible via the simultaneous recording of the signal using a stabilized reference laser maintaining a known wavelength.
  • The width of the wavemeter's scanning range limits the validity of a signal's oscillation period.
  • With equipment of exceptional reliability, results are subject to variances in optical input power as well as detector noise.

 

While build quality plays a part in determining the potential integrity of the component, this category yields accuracy of 0.01 nm.

 

Fizeau interferometer-based: The mechanisms engage dual plane reflecting surfaces with minor deviations from a parallel orientation. An example is a device containing a glass wedge having an angular offset of one to two arcseconds. This setup comprises a front surface demonstrating partial reflection and a fully reflecting back surface. Implementations featuring discrete mirrors exist as well.

 

The structures superimpose two separate copies of an input beam at a slight angle. This results in an interference pattern, with a period depending on the wavelength. The input beam first passes through a spatial filter. Then, a collimated beam of a sizable diameter is supplied to the Fizeau interferometer. At this point, the CCD array or a similar detector assesses the shape exhibited by the interference pattern. The derived data is delivered to the microprocessor for analysis.

 

How Wavelength Meters Work

 wavelength meters specification guide

Electromagnetic radiation is emitted in streams of zero mass particles known as photons. Each particle travels at the speed of light in a pattern similar to a wave. Individual photons contain a specific quantity of energy that determines the frequency of radiation. Particles with low intensity consist of radio waves while the microwave category presents slightly higher energy levels than radio waves. Infrared photons possess amplified energy amounts compared to microwave sources. The levels continue to rise in the following order: visible, ultraviolet, X-rays, and gamma rays.

 

Electromagnetic radiation is calculated as energy, wavelength, or frequency. Hertz, also known as cycles per second, represents frequency. The wavelength is specified in meters and energy in terms of voltage. All three of the indicators relate to each other via mathematical formulas.

 

The unit denoting each form of EM radiation is determined, to a large degree, by its ease of use in relation to the radiation source subject to measurement. The study of radio waves by astronomers involves wavelengths or frequencies. Astronomers quantifying infrared and optical radiation opt for wavelength as their measure of choice.

 

Ultraviolet, X-ray, and gamma rays possess nominal wavelengths. As a result, energy, calculated as electron volts, indicates photon computations.

 

Standard wavemeter calibration is based on waves passing through free space at 299,792,458 meters per second. This allows the determination of wavelengths through an equation with the wavelength (λ) equated to the propagation speed (c) divided by vibration frequency (f), with the last measurement in hertz.

 

Tuned inductance-capacitance circuits serve in quantifying frequencies in the range 50 kHz (thousands of hertz) and 1,000 MHz (millions of hertz). Once values for inductance and capacitance are acquired, the applicable formula computes frequency. When assessing amplified frequencies, the products employ tools, including coaxial lines and cavity resonators serving as tuned elements. Simple methods engage Lecher wire wavelength meters, consisting of a sliding short circuit. By discovering two points where the short circuit enables maximum signal absorption, it is possible to obtain a direct measurement of a distance amounting to half a wavelength.

 

Applications

 

Wavelength meters cover a myriad of applications, including:

 

  • Research & university laboratories
  • Elemental spectroscopy
  • Rubidium spectroscopy
  • Laser cooling/trapping
  • Differential-absorption LIDAR
  • Dense wavelength division multiplexing (DWDM)
  • Manufacturing

Selecting Wavelength Meters

 

Wavelength meters are available in an assortment of configurations. Selecting a device will depend on the purpose and desired precision level characteristics. Essential attributes to consider include:

 

  • Select units come with an autocalibration feature, as frequent calibration is at times necessary to achieve exact values.
  • Some versions may integrate internal reference lasers while alternative solutions rely on external sources.
  • Static options are easier to operate when measuring wavelengths of pulsed inputs (scanning interferometers also perform this function). Typical models feature increased speed compared to non-static versions. Input is provided in the form of a laser beam in free space or through a fiber-optic connection.
  • Certain structures perform better than others when measuring extreme wavelength regions.
  • Display and software functionality varies across products, with some meters capable of displaying wavenumber, linewidth, and optical frequency information in addition to wavelength.

 

Most commercial mechanisms employ either Fizeau or Michelson interferometers. Currently, Fizeau-based units are considered capable of providing readings of enhanced precision. However, they require greater capital costs than competing technologies. They are also constrained to computing wavelengths falling below 2.25 µm. Achieving premium levels of accuracy necessitates more frequent calibration, making autocalibration a valuable attribute.

 

Image Credits:

Bristol Instruments | Newport Corporation