Pulsed Energy Measurement Systems
- Various Heads allow measurement of laser energy from 50pJ to 10J
- Heads for 0.3 - 1.1µm (silicon), 0.8 - 1.8µm (GaInAs) and 0.3 - 30µm (pyroelectric)
- Fast output monitors Pulse Power or Shape with <1.4ns rise time.
- Choice of Battery or Mains operation.
- Integrating Sphere allows a wide range of beam angles and beam positions
- Readout Units capture pulse energy from repetitive and single shot lasers
We offer a variety of systems for measuring the energy and power of pulsed lasers whether they be repetitively pulsed or single shot. Fast photo diodes are usually used in the visible to near infra-red region (0.3 - 1.1µm) and pyroelectric detectors for the longer wavelengths (1-30µm).
The Photo Diode Heads measure both the pulse energy and pulse power. The pulse energy can be read by a slow ’Scope (1MΩ) or by our battery powered Pulse Acquisition Unit. The fast BNC output showing pulse power and pulse shape with <1.4ns rise time needs a fast ’Scope (50Ω). For longer wavelengths, the Pyroelectric Head can be used for energy measurements but has no fast pulse shape output.
Any of the Heads can be used with the Model 19 Data Acquisition Module to acquire energy data or with the Model 8 Peak Power Module to acquire power data. Each has a Digital Display and opto-isolated computer interface. Both these Modules plug into our Standard PSU Rack. Alternatively, there is a battery powered Acquisition Unit (Model 40).
There is also a self contained Unit ( PLEM = Pulsed Laser Energy Monitor) which contains its own polarization compensated beam splitter and on board acquisition circuit to give readings of pulse energy. This also has an output for a fast ’Scope to give pulse shape with <1.4ns rise time.
Beam Direction
All the Heads have an integrating sphere diffusing system so that the sensitivity is almost independent of beam position and beam angle over the allowed range.
Calibration
All our Instruments have calibrations traceable to UK National Physical Laboratory. Typical absolute accuracy is ±3.0%.
Photo Diode Heads
A Diffusing Head is the most generally useful. The geometry with the detector facing the centre of the diffusing sphere ensures a sensitivity essentially independent of beam position or beam angle. Use the Lens Heads or Fibre Optic Heads only for measurement of the smallest energies.
The measurable power ranges given below are simply those that correspond to the maximum or minimum energy sensitivities. For measurements of much lower powers please see details of our Peak Power Meters.
All the Photo Diode Heads need 54V bias. This can come from a small battery pack or from the Model 40 Pulse Acquisition Unit or from the mains powered PSU Rack. The PSU rack is also needed with a Model 19 Data Acquisition unit or a Model 8 Peak Power Module.
Diffusing Head (Model 27)
With the detector facing the centre of the sphere, the signal is independent of beam angle and position.
This system attenuates the light by ×103 - ×108
Lens Head (Model 49)
By collecting all the light directly onto the detector a very high sensitivity is achieved.
The diffuser spreads the light across the detector thus allowing the maximum possible linear photocurrent.
Fibre Optic Head (Model 50)
Any of the standard Fibre connectors can be supplied.
The diffuser ensures that the sensitivity is the same whatever the power distribution within the fibre.
Linearity and Range of Energies
Each Head is individually made for your particular application with the appropriate diffusers and attenuators in front of the detector to keep it within the linear range. Heads can be made to cover anywhere from a few µJ to 100J,with peak pulsed powers from a few mW to 1GW. Any given head can usually measure a factor of 2000:1 in energy and 100:1 in pulse power.
The parameters of our standard designs are shown below with maximum and minimum sensitivities. However, please enquire if you wish to vary any of them: special designs do not necessarily cost significantly more.
| Diff. Head Model 27 |
Lens Head Model 49 |
Fibre Head Model 50 |
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|---|---|---|---|---|
| Max. Poss. Sens: | Energy o/p (1 MΩload) | 1.0V/µJ | 0.2V/nJ | 0.2V/nJ |
| Useable Energy range | 10nJ - 3µJ | 50pJ - 15nJ | 50pJ - 15nJ | |
| Measurable Power range | 100mW - 30W | 1 - 300mW | 1 - 300mW | |
| Min. Poss. Sens: | Energy o/p (1 MΩ load) | 5.0V/J | ||
| Useable Energy range | 2.0mJ - 0.3J | |||
| Measurable Power range | 40kW - 12MW | |||
| Aperture: | 20mm (<2% change) | 20mm (<3% change) | PC/FC Coupler | |
| Acceptance angle: | (either side of axis) | ±30% (<2% change) | ±3.0° (<3% change) | |
| Calibration Accuracy: | ±2.5% | ±3% | ±4.0% | |
| Head Size (length × diam.): | 72 × 74 mm | 70 × 74 mm | 70 × 74 mm | |
| Energy BNC: | Signal Level: | up to 3.0V (proportional to energy) | ||
| Output impedance: | 1 MΩ (always use 1 MΩ load at ’Scope) | |||
| Minimum pulse length: | 100ps | |||
| Maximum pulse length: | 20µs | |||
| Max. Rep.rate: | 200 pulses per sec. | |||
| Power BNC: | Signal Level: | up to 3.0V (proportional to peak power) | ||
| Output impedance: | 50Ω (always use a 50Ω load at 'Scope) | |||
| Response time: | Step edge gives 10 - 90% rise in <1.4ns. An impulse gives FWHM of <2.0ns | |||
| Minimum pulse length for accurate power measurements is 5ns | ||||
| Spect. Range: | 0.3 - 1.06µm (other detectors may also be available) | |||
| Mounting: | M6 tapped hole (= 'OBA') (This accepts most of the bench rods currently in use) |
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| Variants: | Other apertures are available. eg 7mm as needed for safety checks. A longer integrating time constant would allow a longer pulse duration but require a lower PRF. There is a further range of Heads for very low power measurements with NEP down to 3.5nW/cm2 RMS. Details are on the Web Page on Peak Power Measurements. |
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Pyroelectric Head
This head also consists of a spherical cavity with diffusing walls with a pyroelectric detector facing the centre of the sphere. Because diffusers for use in the far infra-red are not very satisfactory, there is some dependence of the signal on the beam position and the angle on the sphere surface. Also, pyroelectric detectors give some piezoelectric ringing about 10MHz following a short impulse. This means that pulse shape and peak power measurements are not possible with any precision. Thus the output socket provides energy measurements only.
| Wavelength Range: | 0.5 - 20µm |
|---|---|
| Sensitivity: | 10V/mJ (Other values may be possible) |
| Output: | 0 - 10V from BNC socket at 1 kΩ impedance |
| Response time: | Signal rises with 1/e time of 60µs then decays with 1/e time of 4ms. |
| Input Aperture: | 18mm |
| Max beam size: | 14mm (limited by diffuser curvature) |
| Min beam size: | 4mm (limited by speckle pattern effects) |
| Positional dependence: | <4% change as beam is scanned horizontally
<5% change as beam is scanned vertically |
| Head size: | 63mm diam × 93 mm long |
| Mounting: | M6 tapped hole (= 'OBA')
(This accepts most of the bench rods currently in use) |
Pulsed Laser Energy Monitor
This instrument provides a complete beam sampling and pulse acquisition system to measure the output of a pulsed laser. It contains a polarisation compensated beam splitter to sample the beam and a diffusing sphere to give a constant signal for any beam position or beam angle within the input and output ports. Range plates can be inserted in front of the detector to give different sensitivities and allow for different wavelengths. Thus the same Instrument can cover a huge range of energies and wavelengths. It has outputs for pulse shape and pulse energy. The output signal can be referred to the energy leaving the Monitor or to that entering the Monitor. It can be self triggering or triggered externally from the laser.
| Wavelength range: | 0.35 - 1.06µm |
|---|---|
| Energy Range with maximum sensitivity: | 10µJ - 1mJ |
| Energy Range with minimum sensitivity: | 300mJ - 10J |
| Max rep. rate: | 20kHz at 12µs duration, 500Hz at 1.5ms duration |
| Min rep. rate: | Acquires energy reading in a single shot |
| Transmission: | 80% |
| Max beam size: | 38mm |
| Overall size: | 26cm long × 18cm high × 12cm wide (Display Meter 16 × 12 × 5 cm) |
Full details of this Instrument are available in our Brochure “Pulsed Laser Energy Monitor”
Data Acquisition
All the Heads detailed in the previous pages will need some system to display their output. Most needs can be met conveniently by using a ’Scope. You should use a load of 1MΩ for the signal from the energy output socket and 50Ω for the power/pulse shape socket. For a more convenient system without ’Scope or for data logging applications you may prefer to use one of the Data Acquisition Units. They all provide the HV bias needed for the Photo-diode.
- Model 40 is a portable battery powered display unit. It acquires the energy value from any Head.
- Model 19 is powered from our standard PSU rack. It also acquires the energy from any Head.
- Model PPM/1 is also powered from our PSU rack. It acquires the peak power from any Head
(1) Model 40 Battery Powered Acquisition Unit
Takes the energy signal from the Head, captures the top of the decaying waveform and displays it on an analogue meter. The display is automatically updated at each successive laser pulse and the reading remains valid until the next pulse. Thus it is equally useful for repetitively pulsed or single shot lasers. It operates only on the energy output from the Head.
| Range switch: | The Range switch will be engraved to suit your application such as: 1, 3, 10, 30, 100µJ/CM2 or 10nJ, 30nJ, 100nJ, 300nJ, 1J |
|---|---|
| Sensitivity: | Full scale on the Meter with 100mV, 300mV, 1.0V, 3.0V, 10V These correspond to different energies depending on the sensitivity of the Head. The sensitivity will be adjusted to suit the exact sensitivity of the particular Head. |
| Rep. rate: | From a single pulse up to 100 pulses per sec. Higher rep rates may be possible. |
| Output Signal: | 0 - 2.0V from BNC socket for DVM or ’Scope (output impedance 1KΩ) |
| Triggering: |
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| Size: | 185mm long, × 130mm wide × 70mm high. |
(2) Model 19 Data Acquisition Module
Plugs into our standard PSU rack. It acquires the pulse from the energy socket on the Head with an accuracy of 12 bits (l/4000) and displays it on an on-board Panel Meter. An opto-isolated computer interface allows good data-logging without introducing noisy earth loops into the system. It must be triggered by a pulse within 2-3µs on either side of the laser pulse.
| DC output: | 10V corresponds to FSD on Panel Meter. Output impedance is 45Ω. |
|---|---|
| Repetitive Rate: | From a single pulse up to 1kHz. Higher rep rates may be possible. |
For further details please ask for Data sheet on Model 19 Data Acquisition Module.
(3) Model PPM/1 Peak Power Module
Plugs into our standard PSU rack. It acquires the pulse from a power socket on the Head and displays it on an on-board Panel Meter. It is entirely self triggering but requires a stream of essentially constant pulses to capture the peak of the pulse. Normally it would display the average value of the peak power but can be switched to display the maximum peak power achieved or the minimum peak power achieved.
| Sensitivity: | This will be adjusted to suit the Head so that it reads in mJ, µJ etc. |
|---|---|
| Pulse duration: | 6ns to 2.5µs (less than 3% variation in reading) |
| Pulse rep. rate: | From 20Hz up to 200kHz. (slower rates may be possible) |
| Output Signal: | 2.0V from 1 kΩ corresponds to FSD on Meter. This can drive an external DVM. |
For further details of the operation of the Peak Power Module ask for data sheet PPM/1.
