MesaPhotonics VideoFROG FROGscan, Руководство пользователя

Страница: 9 / 71

Chapter 1. Overview
09/07/2018 Vs 003 FROGSCAN USER’S MANUAL Page 3
1.4 FROGscan System Components and Beam Path
1= Entrance Iris
2= Center Iris
3= Beam Splitter
4= Servo Mirror
5= Focusing Mirror
6= Fixed Delay Mirror
7= Overlap Mirror
8= Exit Iris/Fixed Delay
Beam Camera
9= Focusing Mirror Camera
10= Diverter Mirror
11= 1
st
Turning Mirror
12= SHG Crystal
13= 2
nd
Turning Mirror
14= Lens + Iris
15= 3
rd
Turning Mirror
16= Spectrometer
Figure 1. Keyed image of the internal FROGscan Ultra component, including optional alignment cameras.
FROGscan Standard is not equipped with the Lens/Iris and 3
rd
Turning Mirror.
The LASER beam (red) enters through the Entrance Iris and is split into 2 parts by the Beam Splitter. The
Servo Beam (dark green) travels to the time delayed Servo Mirror and from there to the Focusing Mirror.
The Fixed Beam (light green) is reflected by the Fixed Delay Mirror. Part of the Fixed Beam travels
through the Overlap Mirror and from there to the Exit Iris (Fixed Delay Beam Camera in instruments with
the camera option). The other part is reflected by the Overlap Mirror and travels to the Focusing Mirror.
The Fixed Beam and the Servo Beam meet on the 1
st
Turning Mirror from where they are directed
through the SHG crystal to generate the Signal Beam (purple).
In FROGscan Ultra, the 2
nd
Turning Mirror directs the Signal Beam through the Lens/Iris, where the Servo
Beam, the Fixed Beam and their respective harmonics are shuttered out by the iris. The Lens focuses the
Signal Beam onto the 3
rd
Turning Mirror from where it enters into the Spectrometer. In FROGscan
Standard, the Servo Beam and the Fixed Beam travel to the 2
nd
Turning Mirror from where they are
directed to either side of the Spectrometer Aperture. Only the Signal Beam enters into the Spectrometer.
The Servo Beam (A) and the Fixed Beam (B) each generate a second harmonic (A*A and B*B) through
interaction with the nonlinear SHG crystal. The Signal Beam (A*B) is produced only when the Servo
Beam and the Fixed Beam overlap temporally and spatially in the crystal (see Figure 2 below).
Figure 2. Second Harmonics generated through
interaction with a nonlinear crystal. The fundamental
beams, A and B, pass through the crystal and
generate second harmonics (SHG) A*A and B*B.
The signal, A*B, is formed by mixing the two
fundamental beams. Depending on the wavelength
of the LASER and the type of crystal and
spectrometer used, both halves of the split LASER
beam, each of their harmonics, and the Signal Beam
can be seen on a fluorescing card.