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The polarity of the PZT can be determined as follows:
Unmounted piezo with cabling as provided by Toptica.
This step is only necessary once when replacing an old piezo. Remove the nut from the BNC connector and cable. Thread the cabling through the mounting hole. Put the nut back on and fix the BNC connector.
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| Fig. A | Fig. B | |||
| Fig. C | Fig. D |
Many TOPTICA products use stacks of piezoelectric transducers for the precise fine-adjustment of cavity lengths in order to tune a laser frequency or to scan a resonator (FPI, SHG).
They are wear-and- tear-elements that need to be replaced at times. The following FAQ will shortly describe the main factors contributing to the aging of PZT. With help of this FAQ we aim at helping you to optimize the lifetime of your piezo.
1. Mechanical strain:
In some cases the PZT operates against a mechanical force, e.g. the solid state hinge in the DL100 series. In this case the force from the hinge constitutes a shear-force on the piezo. Due to the ceramic nature of PZTs this can be a problem. TOPTICA has taken this into account by implementing PZTs with ball heads in these cases. You should keep in mind, however, that for extreme (widely opened hinges) the shearing force might lead to a failure of the PZT. Another reason for being careful with the hinge is the imminent risk of over-stretching it. As a consequence it would lose its elasticity and also the resonance frequency will change (see also the remarks below).
2. Static operation:
When operated under static (or near-static) conditions, humidity (H) and operating DC-voltage (V) are the most important factors that limit the lifetime of a PZT. Their effect can be expressed as follows:
Lifetime ≈ (1/V)3 (1/H)5
As one can see, the two parameters have a rather drastic impact. There is an interplay between DC-voltage and humidity. A high DC voltage level accelerates the diffusion of water molecules into the crystal, which leads to a subsequent deterioration and finally a breakdown. It is therefore advisable to maintain a low DC-voltage level. For instance one should try to tune the laser as close as possible to the desired wavelength without having to maintain a high DC-offset on the scan control module.
Also a low humidity level is of course good. Most piezo failure occur during or after summer when humidity levels are usually higher than during the winter.
3. Dynamic operation
Here both mechanical and thermal factors need to be considered. Firstly the PZT should be operated well below the resonance frequency of the mechanical system the PZT is integrated into. Typically 1.5 kHz is the limit here for DL-, TA- and older DLX systems (built earlier than 2005). For the newer DLX modulation frequencies should not exceed 4 kHz.
Secondly one should be aware that driving the piezo at high frequencies AND amplitudes will result in strong internal heating which can lead to a failure as well. Here one should pay attention in cases where the piezo is part of a feedback loop (for instance for stabilizing the laser frequency against an external reference). In a worst case scenario the aforementioned scenario with high frequencies and amplitudes can occur if the regulators starts to oscillate.
Delta Brechungsindex / Delta temperature (bei 780nm, 35%, 100kPa): -9.07e-7/K
Delta Brechungsindex / Delta pressure (bei 780nm, 25°C, 35%): 2.62533E-6/kPa
Delta Brechungsindex / Delta humidity (bei 780nm, 25°C, 100kPa): -1.14179E-8/%
For the DL 100 that consists of a resonator with a 20.8mm air gap this leads to the following frequency changes with respect to "standard conditions" (780nm, 25°C, 100kPa, 35%):
D Frequency / D temperature: +218MHz/K
D Frequency / D pressure: -631MHz/kPa
D Frequency / D relative humidity: +2,7MHz/%
Typical fluctuations over the course of one day in a lab could be:
D Temperature / day: 2K result in a frequenzy drift of +440MHz (this does not include frequency shifts by mechanical effects but only the air temperature)
D pressure / day: 0.2kPa (mean variation over day) results in a frequenzy drift of -130MHz, large variation of up to 1kPa are possible as well -> drift of -630MHz (!!)
D relative humidity / day: 5% result in a frequenzy drift of +14MHz
The answer depends on the amount by which you want to change the wavelength. Please note that the ranges given below are guidelines for diodes implemented into the DL 100. Standard diodes can be tuned over about 10nm, while AR-coated laser diodes can be tuned over 50nm and more. Please note also that the gain profile of tapered lasers/amplifiers is usually about 10nm wide,
The DL 100 is user serviceable to a certain extent. In order to guide you towards locating and solving the most common problems we are making a troubleshooting workflow diagram available for download.
Before you start
These troubleshooting guides represent only a coarse outline of the steps necessary to get the laser system back to its specification. They do only complement, not replace the user manuals.
Before taking any of the following steps the user must familiarize himself with the hazards involved when mainting a laser source. READ AND FOLLOW THE SAFETY INSTRUCTIONS AND WARNINGS in the user manual carefully before you proceed. TOPTICA can not held be liable for injuries and / or damages caused by improper use of its lasers. If you feel unsure, please contact TOPTICA's service department first. Proceed at your own risk!
This question predominantly arises for diodes with wavelengths greater than 1000nm where many cameras become insensitive and thus direct observation of the light is difficult. In this case we recommend the use of a power meter. In order to find a good starting point one can set the grating angle according to the wavelength, where the grating angle is defined between the collimator-/laser diode-holder (perpendicular to the beam) and the grating holder (front side on which the grating itself is mounted). In the table below the grating angle for selected wavelengths are given:
