FPS-1

Ophir's temporal sensors do not require calibration.

With a temporal detector you can measure the rise time, fall time, pulse duration and pulse frequency. Many laser applications use pulsed laser, for example medical lasers, LIDARs, and high power fiber laser for metal processing to name a few. The parameters of the laser pulses are critical for the performance of the application.

Pulse energy can be measured directly using one of Ophir's calibrated energy sensors. Another way is to use a calibrated power sensor and calculate the pulse energy using:

Pulse energy [J] = average power [W] / pulse rate [pulses per second]

Temporal sensors provide a signal that is proportional to the instantaneous power output of the laser. When viewing the pulse waveform on an oscilloscope, the integrated area under the curve is proportional to the total pulse energy.

Calibrated power sensorsmeasure the average power of CW and pulsed laser beams. The sensor is connected to an Ophir Meter or PC Interface. Power sensors are optimized for low noise and linear response in order to maximize power measurement accuracy. The measured laser beam must be smaller than the sensor's aperture in order to obtain an accurate power measurement. Temporal sensors are optimized for high speed response in order to reproduce pulse temporal characteristics with high fidelity. A temporal sensor is usually smaller than the laser beam size and samples a portion of the beam. The temporal sensor is connected to a scope or spectrum analyzer to display temporal characteristics of pulsed lasers.

There are several possible ways to do this:

• Use a beam sampling optic (partially reflective mirror or uncoated window).
• Feed the laser beam into an integrating sphere and attach the temporal detector to the sphere using the adapter accessory.
• Use a beam dump and position the detector such that it picks up some of the reflected laser radiation.

Attenuating accessories are available (see temporal detector's product page). Laser power density on the attenuators should be less than 50 W/cm².

See the troubleshooting section of the user manual in the temporal detector's product page for detailed information.

There are a number of options, depending on the purpose.

• In many cases, the simplest solution could be to make use of the analog output of the meter – that gives a voltage signal proportional to the actual reading (it is in fact just a D/A translation of what is being displayed), so it represents a fully calibrated reading. The full scale value is a function of the meter being used and the power range it is on.
• The "SH to BNC connector" (Ophir P/N 7Z11010) simply takes the raw output from the detector element and sends it to the scope. It bypasses the sensor's EEROM which contains the calibration data, so it essentially turns the sensor into an uncalibrated "dumb" analog sensor. It should be noted, though, that in some cases we could be talking about a signal to the scope that may be low, perhaps even near the noise level of the scope, which limits the usefulness of this method at low powers.
• If the need is to see the pulse width – the temporal profile – the solution (assuming applicable specs) is to use an approprinte temporal sensor connected to a scope; you can point it anywhere where it will catch some backscatter from your laser, and you'll see the pulse temporal form as it really is.

Admittedly a unit such as “√ Hz” is not very intuitive. In general: Noise Equivalent Power (NEP) is defined as the signal power that gives a signal-to-noise ratio of 1 in a one-hertz output bandwidth. Taking the bandwidth of the measurement into account is where the “square root of Hz” comes in. The noise spectrum typically has a relatively flat response, and the noise level changes with the square root of the frequency range; for example, if the frequency range doubles, the noise component increases by √2 (1.414). In detector datasheets, the bandwidth is typically normalized to 1 Hz (which is usually far below the detection bandwidth), to allow detectors with different bandwidth specifications to be directly compared.