Source code for lasy.profiles.longitudinal.longitudinal_profile_from_data
import numpy as np
from scipy.constants import c
from .longitudinal_profile import LongitudinalProfile
[docs]
class LongitudinalProfileFromData(LongitudinalProfile):
"""
Class for longitudinal laser profile created using data.
The data used can either come from an experimental measurement
or from the output of another code. This data is then used to
define the longitudinal profile of the laser pulse.
The data may be supplied in either the spectral or temporal
domain. The data should be passed as a structure (defined
below). If spectral data is passed, it will be converted to
the temporal domain.
Parameters
----------
data : structure
The data structure comprises several items indexed by
a series of keys
datatype : string
The domain in which the data has been passed. Options
are 'spectral' and 'temporal'.
axis_is_wavelength : boolean (optional, default True)
If True, the axis represents wavelength in [m] (SI).
If False, it represents frequency in [1/s] (SI).
axis : ndarrays of floats
The horizontal axis of the pulse duration measurement.
The array must be monotonically increasing or decreasing.
When datatype is 'spectral' axis is wavelength in meters OR
frequency in 1/seconds.
When datatype is 'temporal' axis is time in seconds.
intensity : ndarrays of floats
The vertical axis of the pulse duration measurement.
Spectral (resp. temporal) intensity when datatype is 'spectral' (resp 'temporal').
phase : ndarray of floats
If provided, this phase will be added to the pulse.
When datatype is 'spectral' phase is spectral phase.
When datatype is 'temporal' phase is temporal phase.
dt : float
Only required when datatype is 'spectral'. In this
case this defines the user requested resolution in
the conversion from the spectral to the temporal
domain.
wavelength : float
Only required when datatype is 'temporal'. Then,
this is the central wavelength of the pulse
lo, hi : floats (seconds)
Lower and higher ends of the required domain of the data.
The data imported will be cut to this range prior to
being incorporated into the ``lasy`` pulse.
"""
def __init__(self, data, lo, hi):
if data["datatype"] == "spectral":
axis_is_wavelength = True # Set to wavelength data by default
if "axis_is_wavelength" in data:
axis_is_wavelength = data["axis_is_wavelength"]
if axis_is_wavelength:
wavelength = data["axis"] # Accept as wavelength
spectral_intensity = data["intensity"]
else:
wavelength = 2.0 * np.pi * c / data["axis"] # Convert to wavelength
spectral_intensity = (
data["intensity"] * 2.0 * np.pi * c / wavelength**2
) # Convert spectral data
assert np.all(np.diff(wavelength) > 0) or np.all(np.diff(wavelength) < 0), (
'data["axis"] must be in monotonically increasing or decreasing order.'
)
if data.get("phase") is None:
spectral_phase = np.zeros_like(wavelength)
else:
spectral_phase = data["phase"]
if np.all(np.diff(wavelength) < 0): # Flip arrays
wavelength = wavelength[::-1]
spectral_intensity = spectral_intensity[::-1]
spectral_phase = spectral_phase[::-1]
dt = data["dt"]
cwl = np.sum(spectral_intensity * wavelength) / np.sum(spectral_intensity)
cfreq = c / cwl
# Determine required sampling frequency for desired dt
sample_freq = 1 / dt
# Determine number of points in temporal domain. This is the number of
# points required to maintain the input spectral resolution while spanning
# enough spectrum to achieve the desired temporal resolution.
indx = np.argmin(np.abs(wavelength - cwl))
dfreq = np.abs(c / wavelength[indx] - c / wavelength[indx + 1])
N = int(sample_freq / dfreq)
freq = np.linspace(cfreq - sample_freq / 2, cfreq + sample_freq / 2, N)
# interpolate the spectrum onto this new array
freq_intensity = np.interp(
freq, c / wavelength[::-1], spectral_intensity[::-1], left=0, right=0
)
freq_phase = np.interp(
freq, c / wavelength[::-1], spectral_phase[::-1], left=0, right=0
)
freq_amplitude = np.sqrt(freq_intensity)
# Inverse Fourier Transform to the time domain
t_amplitude = (
np.fft.ifftshift(
np.fft.fft(
np.fft.fftshift(freq_amplitude * np.exp(1j * freq_phase))
)
)
/ dt
)
time = np.linspace(-dt * N / 2, dt * N / 2 - dt, N)
# Extract intensity and phase
temporal_intensity = np.abs(t_amplitude) ** 2
temporal_intensity /= np.max(temporal_intensity)
temporal_phase = np.unwrap(-np.angle(t_amplitude))
temporal_phase -= temporal_phase[np.argmin(np.abs(time))]
elif data["datatype"] == "temporal":
time = data["axis"]
temporal_intensity = data["intensity"]
if data.get("phase") is None:
temporal_phase = np.zeros_like(time)
else:
temporal_phase = data["phase"]
cwl = data["wavelength"]
else:
raise Exception("datatype must be 'spectral' or 'temporal'")
super().__init__(cwl)
# Finally crop the temporal domain to the physical domain
# of interest
tIndLo = np.argmin(np.abs(time - lo))
tIndHi = np.argmin(np.abs(time - hi))
self.time = time[tIndLo:tIndHi]
self.temporal_intensity = temporal_intensity[tIndLo:tIndHi]
self.temporal_phase = temporal_phase[tIndLo:tIndHi]
[docs]
def evaluate(self, t):
"""
Return the longitudinal field envelope.
Parameters
----------
t : ndarray of floats
Define points on which to evaluate the envelope
Returns
-------
envelope : ndarray of complex numbers
Contains the value of the longitudinal envelope at the
specified points. This array has the same shape as the array t.
"""
intensity = np.interp(t, self.time, self.temporal_intensity)
phase = np.interp(t, self.time, self.temporal_phase)
envelope = np.sqrt(intensity) * np.exp(-1j * phase)
return envelope
