FAQ 1: I just received my laser, but I cannot get it to emit light.

Please check the following points: 

1. Is the control rack/power supply connected to a mains outlet?

2. Is the interlock connector in place?

3. Is the mains switch on the back side of the power supply switched on?

4. Is the key lock switch on the monitor unit switched on?
(If 1 - 4 are fulfilled and still the display module does not come on, i.e. there is no background illumination of the dot matrix display or no welcome message, please refer to FAQ 2).

5. Is the current control module (DCC) connected to the laser head and are the locking screws tightened?

6. Is the DCC operation LED (yellow) on?

7. Is the shutter open?

FAQ 2: The rack does not work (display remains dark).

Please check first points 1 - 4 from FAQ 1.

2. If the display still remains dark, the error might be due to a breakdown in the supply voltages in the power supply. This can be due to a failure in the power supply itself or due to a fault in one of the other modules. To check this, we recommend the following procedure:

3. With the rack switched off (DC/Mon keylock switch) loosen the screws on the front cover plates of the other modules (i.e. DCC, DTC, SC, etc, but not DC/Mon ) and pull them from their slots.

a) If the display comes on the error is caused by one of the other modules. In this case switch the rack off again, reinsert one of the modules, switch the rack on again and check if the display still comes on. Repeat this procedure until the faulty module is identified.

b) If the display still does not work the error is most likely located in the rack power supply.

Please contact our service department by filling out our Service Request Form.

FAQ 3: Is it possible to operate the supply rack without the display unit DC/Mon?

Yes. Please note that the following steps should only be performed by persons who are trained to service electrical equipment! Please read our disclaimer before performing the following operation!

1. Switch off and disconnect the power supply rack from the mains outlet.

2. Unscrew the fixing screws and remove the heat sink at the rear of the Supply Rack as shown in figure 5.10 on page 14, part V of the DL100 manual.

3. On the upper left corner of the printed circuit board locate the jumper labels "test POWon". Connecting the two pins and subsequent reassembly will allow you to operate the rack without DC/Mon.

FAQ 4: Which factors contribute to the lifetime of piezoelectric transducers ("piezos", "PZTs")?

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.

FAQ 5: How do I change the wavelength of my laser?

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,

1. 100 kHz - 30Ghz : offset potentiometer on the SC110 unit

2. 30 GHz - 10nm : micrometer screw on grating holder.

3. 10 nm - 50nm : the grating holder needs to be rotated as a whole (especially relevant for AR-coated diodes). Please refer to the DL 100 manual, part IV, page 29.

4. 50 nm - 500nm : a different diode is needed. Please note that it might also be necessary to use different collimation optics and/or another grating whose characteristics match the new diode.

FAQ 6: Which tools do I need in order to verify that my laser works properly?

We highly recommend the use of a high-finesse interferometer, such as the FPI 100 from TOPTICA for characterizing the spectral properties of your laser, such as single-mode operation and mode-hop-free tuning range. Our experience shows that customers without such a tool spend significantly more time verifying correct operation of their laser system.

A well calibrated spectrometer such as an optical spectrum analyzer or a high precision wavelength meter (e.g. the WSx series from High Finesse) also proves useful for precise and rapid coarse tuning of the laser. This is especially important if the laser is operated at wavelengths where no atomic/molecular reference exists.

FAQ 7: I want to realign my laser cavity but I cannot locate feedback (flashing).