Is there a coolant pressure specification for Ophir water-cooled sensors?

Yes. Please reference the chart below:

Minimum Flow Rates for Water-Cooled Sensors

Sensor Recommended flow rate at full power1
(liters/min)
Minimum flow rate at full power1
(liters/min)
Absolute minimum flow rate
(liters/min)
pressure drop across sensor
(bar, at maximum flow rate)
Pressure drop across sensor
(MPa)
L250W 3 3 3 0.3 0.03
L300W 3 3 3 0.3 0.03
1000W 6 3 3 0.3 0.03
L1500W 6 3.5 3 3 0.03
L2000W 6 3.5 3 0.6 0.06
5000W 8 5 3 0.6 0.06
6K-W-200x200 6 6 5 0.5 0.05
10K-W 8 8 3 1 0.1
15K-W 12 12 3 2 0.2
16K-W 12 12 3 1 0.1
30K-W 25 25 6 2 0.2
120K-W 60 60 30 4 0.4

You can find a lot more information about the correct use of water-cooled sensors in the article "How to use water cooled Ophir sensors", here.