Datasheet

4.3 QCL spectra

4.3.2. Linewidth of pulsed single-mode DFB QCLs

The linewidth of DFB QCLs operated in pulsed mode depends on the pulse length,

and is affected by chirping, which occurs because of thermal variations of the laser.

• Fine linewidth is obtained with short pulses (25 to 50 ns). ALPES LASERS QCLs

are tested using pulse length of 25 to 50 ns, showing a linewidth < 0.2 cm

−1

• Very ﬁne linewidth (< 0.1 cm

−1

) is obtained with pulses of 10 ns, which can be

produced by dedicated equipment only.

• Longer pulses (> 50 ns) induce chirping, producing a broader linewidth when

detected with a slow detector.

ALPES LASERS standard tests verify that DFB QCLs are singlemode, i.e. have a

linewidth not exceeding 0.2 cm

−1

with pulses of 50 ns.

Note: ALPES LASERS QCLs are characterized with a pulse length of 50 ns, but

some QCLs may withstand pulse lengths up to 400 ns.

IMPORTANT:

The maximum pulse length an ALPES LASERS DFB QCL operated in pulsed mode

can withstand is of typically 200 ns. Requirements for operation with pulses longer

than 50 ns must be speciﬁed before purchasing a laser.

IMPORTANT:

The operating parameters are speciﬁed in the datasheet provided with each laser

upon delivery; any operation outside the speciﬁed range must be agreed with ALPES

LASERS or may result in the loss of warranty.

4.3.3. Linewidth of CW single-mode DFB QCLs

DFB QCLs operated in CW mode reach thermal equilibrium with pulse length of 10 ms

and longer. In this case, transient behavior affects only the beginning of the pulse, and

can be neglected. The linewidth is therefore limited by thermal noise and electronic

noise produced by the driver. Very long pulses (>100 ms) will behave in a CW manner,

and shorter pulses will exhibit chirping as pulsed lasers do, and may induce multi-

mode behavior.

IMPORTANT:

ALPES LASERS QCLs operated in CW mode are guaranteed to be single mode if

operated with long pulses (> 10 ms) only.

2012 SA 47