Merge branch '60-update-laser-frequency-noise-noise-shape' into 'master'

Resolve "Update laser frequency noise noise-shape"

Closes #60

See merge request !87

lisainstrument/noises.py

@@ -133,18 +133,22 @@ def infrared(fs, size, asd):
     return np.cumsum(red_noise) * (2 * pi / fs)
 
 
-def laser(fs, size, asd=28.2):
+def laser(fs, size, asd=30, fknee=2E-3):
     """Generate laser noise [Hz].
 
-    This is a white noise,
+    This is a white noise with an infrared relaxation towards low frequencies,
+    following the usual noise shape function,
 
-        S_p(f) = asd^2.
+        S_p(f) = asd^2 [ 1 + (fknee / f)^4 ]
+               = asd^2 + asd^2 fknee^4 / f^4.
 
     Args:
         asd: amplitude spectral density [Hz/sqrt(Hz)]
+        fknee: cutoff frequency [Hz]
     """
-    logger.debug("Generating laser noise (fs=%s Hz, size=%s, asd=%s Hz/sqrt(Hz))", fs, size, asd)
-    return white(fs, size, asd)
+    logger.debug("Generating laser noise (fs=%s Hz, size=%s, asd=%s Hz/sqrt(Hz), fknee=%s Hz)",
+        fs, size, asd, fknee)
+    return white(fs, size, asd) + infrared(fs, size, asd * fknee**2)
 
 
 def clock(fs, size, asd=6.32E-14):