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HighFinesse-Ångstrom Wavelength meters

Options for our wavelength meters

In addition to our wavelength meters for standard-, UV- and IR-measurement range, several options are avialable. The flexible design of the wavelength meters permits the integration of additional optical components and software modules, allowing custom solutions for customer specific applications. Standard options include:

» Linewidth option - L
» Diffraction Grating Hybrid Option - D
» Double-Pulse Option - DP
» Multi Channel Switch - MC
» External TTL Trigger Option - TTL
» Laser Control Option (PID)


Linewidth Option - L

The linewidth estimation of a single-mode laser source is performed by a special algorithm which eliminates the interferometer’s instrument response function. The algorithm enables the estimation of the linewidth several times better than the interferometer resolution. The linewidth option can also be used for measuring the linewidth of multimode lasers or lasers with sidebands. In this case, the longitudinal mode splitting needs to be less than 300 MHz and the calculated result is the FWHM of the envelope function of the multi-line spectrum. Any instrument can be upgraded with the L-option, single mode fibers are required.

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Diffraction Grating Hybrid Option - D

The diffraction grating option allows the analysis of the emission spectrum to an accuracy of 6 GHz, for laser sources with broad emission (but 1/5 of the width in best case). The software automatically searches the spectral section where the laser emission line is located and displays it on the screen. In combination with the additional Fizeau interferometer array this allows wide range applications
The grating option is available for WS5 and WS6 only.

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Double-Pulse Option - DP

Double-Pulse Option

Simultaneous measurement of two laser wavelengths

Detecting two different subsequent pulses supplied by one fiber and treating them as individual signals is possible using the double pulse option. In this mode the wavemeter is triggered externally. This allows additional applications as pump and probe measurements for instance.

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Multi Channel Switch - MC

Multi Channel Switch

Multi Channel wavelength meter for up to 8 fiber inputs

In order to measure the frequencies of more than just one laser at a time, an opto-mechanical switch (MEMS) is used. The combination of our highspeed wavelength meters with one of the quickest fiber switches (MEMS) available allows the measurement of up to 8 channels almost simultaneously. Exposure time and other parameters can be defined independently for each light source.

Spectral range: 250 nm – 2200 nm
Fiber: Multimode or Singlemode
Lifetime: > 109 cycles
Cycle time: 0.2 sec/8 channels
Peak power: 23 dBm

The multi-channel switch option provides the possibility for auto-calibration. Any well known laser source connected to the switch can be used for wavelength meter calibration as needed. For WSU we recommend singlemode switches. Multimode switches allow only quickcoupling accuracy.

For this option in the delivery is included additionally:
External switch box
5pin lemo cable (switch - wavemeter)
Optical fibers according to switch type

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External TTL Trigger Option - TTL

This option allows the user to trigger pulsed measurements externally. It guarantees synchronization between pulsed excitation and measurement. It gains low-noise and pollution-free signals on measuring pulsed signals with low duty cycles. There are two different ways to trigger:

External Trigger

In mode 1 the TTL-pulses are used to start and stop the measurement. The TTL-pulse triggers the read-out of the arrays. Afterwards the CCD-arrays are illuminated until the next TTL-pulse is detected. In this mode, the illumination is given by the TTL-pulse distances and therefore cannot be set by the program.

External Trigger

Mode 2 triggers the measurement start. After the TTL-pulse and a security period of ~ 10 µs, the sensors are illuminated for a user-defined period of time (integration time ~1 - 10 ms). The laser pulse must not occur within the security zone!

For this option in the delivery is included additionally:
LEMO-cable
BNC-adapter

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Laser Control Option (PID)

Make the laser do what you want it to do! As opposed to bulk error signal generation, the PID option provides full signal processing, accomplished by a software-based Proportional- Integral-Derivative (PID) controller. This option is very useful in experiments where the laser frequency has to fit changing experimental conditions, such as laser cooling, atomic detection, trapping and manipulation as well as Raman spectroscopy and other experiments where the laser frequency has to be actively regulated.

The PID option can do even more: It provides a function generator enabling the user to make the laser’s frequency follow any arbitrary mathematical function, e.g. a sine, triangle, rectangle, stairs, trapezoid functions, etc. or any combination thereof.

Lasercontrol

Combination of a triangle- and sine-modulation of a DFB-laserdiode running at 780 nm:

The add-on program PID-SIM (download) can be used to automatically detect the best regulation parameters and synchronize them with the main program. This method makes it easy to determine optimal regulation parameters. And additionally this program can be used as a regulation database, storing any number of named regulation sets.

The basic idea is to let the wavelength meter read the actual frequency and pass the result to the signal-processing part of the software, i.e. the PID option. By comparing the measurement result to the desired setpoint, an error signal is generated. The error signal is used by the software PID-controller to calculate the control signal which mainly consists of three contributing parts:

 To "handle the present", the error is multiplied by a proportional parameter P. P is always negative, to drive the output toward the setpoint. The proportional part cares for regulation speed.

 To "handle the past", the error is integrated over a period of time, and then multiplied by the parameter I. The integral part is slow but can take setpoint errors into account.

 To "handle the future", the first derivative of the error (its rate of change) is calculated with respect to time, and multiplied by the dericative parameter D. This enables the controller to compensate over regulations and resident errors (drift).

The principal function for a PID controller is:

Formula

The single parameters of the proportional (P), integral (I), and derivative (D) parts and the total output gain (V/nm) can be set independently or generated automatically PID-SIM (download) .

SettingsSettings

Settings of PID-controller and sensitivity

This option is very useful in experiments, where the laser frequency has to fit changing experimential conditions, like laser cooling, atomic manipulation and detection, raman spectroscopy, etc.

For this option in the delivery is included additionally:
LEMO-cable
BNC-adapter

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Last update: 18.10.2013 © HighFinesse GmbH 2014