Datasheet

CHAPTER 2. ELECTRICAL AND OPTICAL PROPERTIES 8
2.1.3 What is the lifetime of the laser (MTBF)?
At present only extrapolated lifetime experiments have been performed and they show
more than 10 years extrapolated lifetime at 20C. The measurements have been done
operating devices under N2 atmosphere at 130C in pulsed mode at 130% of threshold
current. (An activation energy of 0.7 eV has been used to convert the high temperature
life time of 350 to 500 hours to room temperature life time.)
2.2 Electrical properties
For information about thermal properties, See section 3.1 (Heating and Cooling),p.12.
2.2.1 What impedance does a QCL show?
The impedance of a QCL depends strongly on the wavelength it is designed for, the
temperature and the mode it is operated, therefore only rough indications can be given
here (consult the datasheet of a particular laser for exact behaviour).
Pulsed mode devices have an impedance in the region of 5..50 Ω up to about half
the threshold current, then it decreases to the region of 0.5..5 Ω. When operated at too
high current, the impedance can rise again (a condition to be avoided in any case).
2.2.2 Can I check the impedance with an ohm-meter?
Certainly (as long as the applied current is not higher than 10mA), but it might not
give you a lot of information, since the impedance varies strongly with the temperature
of the QCL, and normal ohm-meters do not specify the applied current. Therefore,
the measured impedance varies also with the resistance range of the ohm-meter, and
between different ohm-meters. This is also the reason why Alpes Lasers SA does not
specify the DC resistance of QCLs.
2.2.3 Where is the cathode of a QCL?
By default, the cathode is connected to the ceramic pads and the anode is connected
to the copper carrier. It may happen that the laser is mounted junction down; this case
is clearly indicated on the laser box, and then the cathode is connected to the carrier
and the anode to the bonding pads.
2.2.4 How do I drive a pulsed QCL? Can I use a standard laser driver?
Unfortunately, it is in general not possible to use a standard laser driver for a QCL, as
in most cases the compliance voltage, current and rise/fall time are not compatible.
Requirements for a pulsed QCL:
• pulse current of up to 10A
• voltage of up to 12V