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SolsTiS User Manual v10.0
The range of possible frequencies that could, in principle, oscillate is
determined by the width of the Ti:S gain envelope, while the modes that do
oscillate in practice are determined by laser cavity design and pump power.
Various optical elements may be added to the cavity to restrict the number of
cavity modes that can oscillate (ultimately to only one mode for SLM
operation).
Narrow Linewidth Operation
– SolsTiS Cavity Design
Figure 11 illustrates the layout and key elements of the SolsTiS cavity.
Figure 11
Schematic illustration of SolsTiS intracavity layout and
reference cavity (SolsTiS model -SRX).
The SolsTiS laser’s ability to achieve ultra-narrow linewidths is result of many
innovative features incorporated into its electronic and mechanical design,
including: a sealed, miniaturized, monolithic housing and compact laser cavity;
up-to-date, low noise DSP electronics; and the use of proprietary M
Squared InvarianT™ alignment-free and drift-free opto-mechanical
mounts. The mechanical design features in particular give the laser
a high level of inherent stability, and consequently an inherently
narrow passive linewidth. This mechanical platform then provides a
firm foundation upon which to build an electronic servo locking
system capable of reducing the laser linewidth to sub-50kHz
(measured relative to the reference cavity). A first for a laser of this
type, all adjustments in SolsTiS are hands-free and computer
controlled via the included software UI.
In order to enable SolsTiS to oscillate on a single frequency (if
required), spatial-hole burning effects in the gain medium must be
removed. This is achieved in SolsTiS by using the well-known bow-
tie ring cavity geometry. This, together with an optical diode, forces
the ring cavity to operate uni-directionally, resulting in a traveling
wave that ensures a minimum of spatial-hole burning.
In order to
tune SolsTiS’ output wavelength, a motorized intracavity
birefringent filter (BRF) is used. The BRF introduces a wavelength-
dependent loss into the cavity, and wavelength tuning is
accomplished by rotating the BRF. As can be seen from Table 2 all
SolsTiS models contain a BRF. The BRF provides a relatively rapid
but coarse wavelength adjustment. If, in addition, narrow linewidth
operation is required, an intracavity thin étalon is added to the cavity
(SolsTiS model
–PX). The étalon introduces a spectral loss into the
cavity that is a much sharper function of frequency than the BRF,
and by electronically adjusting the étalon spacing, SolsTiS’ output
frequency may be tuned. The excellent passive stability of SolsTiS
means that, unlike many other designs, SolsTiS can often operate
single frequency for relatively extended periods without active
stabilization of intracavity frequency selective elements. In general,
however, while SolsTiS’ output will tend to be single longitudinal
mode (SLM), without active stabilization it may also spend periods
oscillating on two or more frequencies, depending on pump power