# How do I change the phase of fields obtained from frequency-domain monitors?

| Date       | Category    |
|------------|-------------|
| 2023-12-19 20:07:15 | Monitors |


You can use the <code>apply_phase()</code> function to change the phase of fields obtained from frequency-domain monitors. For example:

 



```python
import numpy as np

# Run the simulation and get the data.
sim_data = tidy3d.web.run(simulation, task_name="task", path="data/data.hdf5", verbose=True)

# Get data from a field monitor.
field_data = sim_data["field_monitor"]

# Change the field phase by phi.
phi = 90 * np.pi / 180
field_phi = field_data.apply_phase(phi)

```



It's useful in observing resonance details or producing animations.