6
SolsTiS User Manual v10.0
and the magnitude of external perturbations, such as external vibration or
changes in ambient temperature or pressure.
If guaranteed long-term single mode operation is required, electronic servo
locking of the intracavity étalon can be added (model SolsTiS-LX). This locks
the peak of the étalon transmission function to the nearest longitudinal mode
(after tuning, not during tuning). With SolsTiS-P
SX, the user can tune SolsTiS’
output frequency (with high speed but relatively low resolution by adjusting the
BRF, or relatively high resolution by adjusting the étalon spacing). SLM
operation may then be selected and maintained by locking the étalon (to the
nearest cavity longitudinal mode and to within the capture range of the servo
loop) by dithering the étalon spacing.
If in addition, the operator wants to maintain SLM operation as the laser
frequency is tuned, a long-throw PZT-mounted mirror may be added to the
cavity (model SolsTiS-PSX). Adding the computer-controlled PZT allows
SolsTiS’ cavity length to be changed precisely, and to be adjusted to match
the single oscillating longitudinal cavity mode frequency precisely as the cavity
length is tuned. With the étalon peak lock circuit engaged, the peak
transmission of the étalon is then kept locked to this oscillating longitudinal
mode frequency (to within the capture range of this lock circuit), even as this
frequency is tuned by the PZT. With the SolsTiS-PSX, the operator can
therefore: tune SolsTiS’ output frequency (via the BRF and/or étalon spacing);
lock the étalon (by dithering the étalon spacing) to select and maintain SLM
operation; and then electronically tune or scan the SLM output frequency.
If, in addition, the narrowest possible linewidth is required, a high stability,
high finesse, reference cavity can be added to SolsTiS (model SolsTiS-SRX).
By locking the SolsTiS cavity to this reference cavity (which is a temperature
controlled, integ
rated, sealed design with all optics mounted on Invar) SolsTiS’
linewidth can be reduced to less than 50kHz (measured relative to the
reference cavity). Slaving SolsTiS to the reference cavity is accomplished by
directing a small fraction of SolsTiS’ output to the reference cavity, and then
locking SolsTiS’ output frequency to a reference cavity fringe using a SolsTiS
cavity mirror mounted on a fast PZT. (In SolsTiS, a dual stack PZT is used on
one cavity mirror, with one PZT devoted to frequency scanning, and the other
faster PZT devoted to frequency locking.) With the SolsTiS cavity
slaved to the reference cavity, SolsTiS’ output frequency can then
be scanned (or offset) by scanning (or adjusting) the reference
cavity length. By designing the reference cavity so that it uses only
a small fraction of the total available PZT deflection, the reference
cavity length can be adjusted with a high degree of precision,
enabling precise scans of the SolsTiS output frequency. A re-
entrant actuator design in the reference cavity also passively
compensates temperature-dependent changes in reference cavity
length, further enhancing the stability of the reference cavity and
hence stability of SolsTiS’ output frequency. While SolsTiS absolute
frequency drift is very low (typically <100MHz/hr/ºC) SolsTiS may
also be locked to an absolute frequency reference, such as an
atomic absorption line or a third-party high-precision wavemeter.
Locking SolsTiS to an absolute frequency reference and scanning
(typically >25GHz) relative to it is quite straightforward, and
generally requires only that the operator supply SolsTiS with a
suitable frequency error signal, such as the feedback signal from a
wavemeter, or the transmitted or reflected signal from an atomic
cell, and then tune SolsTiS to within the capture range of the locking
circuitry (typically ~2GHz). Gain and offset settings included in
SolsTiS’ UI allow users to condition the error signal to make it
compatible with So
lsTiS’ locking circuitry.
Note!
Locking SolsTiS to an absolute frequency
reference, such as a third-party wavemeter or atomic
absorption line, is generally straightforward but, if
required, please contact M Squared Lasers or an
authorized representative for more information. In
particular, error signals derived from wavemeters can
vary, and may not be compatible with SolsTiS.