Tsunami - Beckman Institute Laser Resource Center

Tsunami
where ti, is the input pulse width in femtoseconds, and D, is a dispersion
value normalized for a given length and wavelength. Table B-2 gives -
values for different materials at 800 nm. Also given in Table B-3 are the
values for some negative dispersion setups, prisms, and grating pairs for
compensation at 800 nrn. Using these values, B is calculated directly; we
define S as:
Using Figure B-5, you can relate the value of S to a value for the broadening
B.
Q,
73
(d
6
-
-
5
h -
c -
4=-
\
a 4 1
V C
0) -
.- c -
s 3 -
-
9 2 m
-
-
-
J
1 4-/
-
-
0
I I
I I I
I
'
( , I
,
I , '
1 -
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0
S (Normalized Units)
/
A/
r-
r
//
Figure B-5: Broadening Curve
When using this equation and graph, it is important to remember that the
values of D, are wavelength sensitive. For example, for BK-7 material,
the difference from 800 nm to 880 nm is 17%. Therefore, it is important to
use the correct value of D, for the operational wavelength. Also, if there
are several materials present, the values for dispersion must be added
before calculating B. For example:
This provides a simple means for calculating the spacing between prisms
-,
necessary for compensation.