Integrating Sphere Heads with a Control Unit
Our Laser Power Meters are designed to make the accurate measurement of laser power as simple as possible. They accept wide divergence beams and give a rapid response yet still provide traceability to UK National Standards for CW laser power measurement.
- Can measure diverging light from end of optical fiber
- Measures power of a CW laser or the mean power of a pulsing laser
- Rapid response time: 0.1 - 0.3 secs
- ±1.6% overall absolute accuracy (traceable to UK NPL)
- Battery powered for low noise, portability and reduced Earth Loops
- Choice of detector type: Thermopile, Si, Ge, GaInAs
Design of Systems for Measuring CW Laser Power
Most systems for the measurement of CW laser power to about 100W use an almost total absorption of the beam on a relatively massive target. This approach can give some or all of the following problems:- (1) The response is usually inconveniently slow. (2) The sensitivity may vary across the target. (3) The sensitivity may drop at high powers due to non-linear cooling. (4) At the highest powers there may be damage to the target.
By using an Integrating Sphere, our laser power meters avoid these problems. The sphere is coated with a robust high reflectivity diffusing paint which spreads the absorption evenly over the whole sphere. Also the power on the detector is reduced to a level well within the linear range. The integrating sphere is carefully designed to give a signal which is essentially independent of beam position, beam size and beam angle. This allows the measurement of the diverging output from an optical fibre (up to a 60 degree cone or +/- 30 degrees on either side of the axis of the fiber).
The standard detector in our integrating sphere is a Thin Film Thermopile. This has a fast response time of 0.2 secs combined with an almost flat spectral response from 0.4 to 1.5µm. For the very lowest powers we offer spheres with a photo-diode (Si, Ge, GaInAs); a thumb-wheel switch then gives the wavelength correction appropriate to each type of diode. On request, the photo-diode systems can have a BNC socket added which will show the pulse shape of a repetitively pulsing laser.
The design of the electronics allows you to measure the mean power of a stream of short pulses. There is a BNC output socket for a chart recorder, DVM or PC.
| Model Name | Detector Type | Spectral Range | Power Ranges | N.E.P. | Aperture | Head Size L × D |
|---|---|---|---|---|---|---|
| Model 55 | Thermopile | 0.4 - 1.5µm | 1mW - 1W | 15µW | 18mm | 74mm × 80mm |
| Model 69 | Thermopile | 0.4 - 1.5µm | 10mW - 10W | 150µW | 25mm | 99mm × 92mm |
| Model 68 | Thermopile | 0.4 - 1.5µm | 0.1W - 100W | 1.5mW | 35mm | 114mm × 112mm |
| M29(Si) | Si Diode | 0.35 - 1µm | Lowest 10µW - 3mW | 200nW | 18mm | 65mm × 74mm |
| Highest 3mW - 1W | 30µW | |||||
| M29(Ge) | Ge Diode | 0.9 - 1.6µm | Lowest 30µW - 3mW | 600nW | 18mm | 65mm × 74mm |
| Highest 3mW - 1W | 100µW | |||||
| M29(GaAs) | GaInAs | 0.9 - 1.7µm | Lowest 10µW - 3mW | 600nW | 18mm | 65mm × 74mm |
| Highest 3mW - 1W | 100µW |
Power Ranges
For the photo diode systems there are 6 positions for the range switch. These ranges can be put anywhere between the sets given as ‘lowest’ and ‘highest’. For example 100µW 300µW, 1 mW, 3mW, 10mW, 30mW.
Other power ranges may be available; please enquire.
Noise/Bandwidth
For the Thermopile systems the NEP is given with the bandwidth switch in the normal position. This gives 10-90% rise time of 80ms at the output BNC. (settling to within 0.5% in 0.2 secs). The bandwidth switch gives a further factor of 2 reduction in NEP but the 10-90% response time is then 400ms (settling to within 0.5% in 1.0 sec).
Max. Power Density
There is a risk of damage to the diffuser if the power density exceeds 20W/cm2. This limit needs to be taken seriously. For example, with M68 receiving 100W, even a really smooth Gaussian beam must have a FWHM of at least 20mm.
Calibration Accuracy
The absolute accuracy of our own Calibration is normally better than ±1.6% at your chosen wavelength. This is traceable to the UK National Physical Laboratory. The Calibration Certificate will also give details of the change expected at the limits of the spectral range.
For Photo-diode systems we will have calibrated it to ±1.6% at your chosen wavelength. For other wavelengths you simply set a digital switch to the new wavelength. The sensitivity then tracks correctly to better than ±5% over the full spectral range for that type of photo diode.
Analogue Display Unit
- Size: 16cm × 9.6cm × 5cm high.
- Weight: 550gms
- Cable to Head: 1.5m screened cable
- Batteries: re-chargeable Metal Hydride (lasts 9 hrs without charging)
- Battery monitor: battery state is monitored continuously
- Ambient back-off: (up to 2x FSD)
- Output BNC: gives 1V FSD from 1kΩ
Analogue and Digital Readouts
Analogue meters are normally strongly preferred because its is easier to follow a trend and they do not suggest an unjustified accuracy. However, if required, a digital display unit can be supplied.
Rapid Pulses
The Display Units are designed to integrate pulsed currents. They show the mean power of rapidly pulsing lasers of any pulse duration with any repetition rate from GHz down to 10Hz. Thus these CW Meters are ideal for measurements of lasers for fiber optic or free space communication or pulsed laser therapy. Below 10Hz the reading will appear noisy and will read low by an amount depending on the duty cycle.
Temperature Effects
- Heads M55, M69 and M68 have a temperature coefficient of -0.4%/°C at all λ
- Head M29 (Si) has a temperature coefficient between -0.3%/°C and +1.0%/°C depending on the wavelength.
- Storage Temp Range: -20°C to +60°C
- Operating Temp Range: +15°C to +25°C
Water Cooling
Heads M69 and M68 have fittings for water cooling. You should use water cooling if you will regularly have exposures to more than 5W for more than about 20secs.
Head Mounting
M6 thread (= 'O' BA). This takes most of the standard optical posts.
Non Standard Systems
About half the systems we sell are non-standard and contain modifications to suit the precise requirements of our customers. These changes do not necessarily cost any more. Please contact us if your exact needs do not appear in this brochure.