How to Choose Pulse Energy for a Laser Rangefinder
*Choosing a laser source starts with a range requirement, not a model number. This article works through how
pulse energy, target reflectance and receiver sensitivity combine into a usable link budget — and where the
1535 nm sources in the ERDI range sit against that calculation.*
In short: pulse energy is one term in the range equation, not the answer to it. Work the link budget first,
decide whether pulse width or repetition rate constrains the design, and the energy tier usually chooses
itself.
Why pulse energy alone does not determine range
A common way to compare laser sources is by pulse energy, and it is a useful starting number — but it does not
determine how far a rangefinder will reach. Range comes from the whole measurement chain:
- how much energy leaves the transmitter
- how much of it the target sends back, which depends on the target's size, surface and angle
- how much the atmosphere takes out on the way there and back
- how much of the return the receiver's aperture collects
- how efficiently the detector converts that light into a signal
- how much noise the receiver chain adds, and what margin the detection logic needs
Change the receiver and the same source reaches further, or less far. Change the target from a cooperative
retro-reflector to dark clothing and the range can drop by an order of magnitude. Pulse energy is one term in
the product, not the answer.
This is why a specification is normally quoted at a stated condition — a particular target reflectance, a
particular visibility, a particular false-alarm rate. When two datasheets give different ranges for similar
pulse energies, the difference is usually in the conditions, not in the source.
The link budget, in the order it is usually worked
1. Start from the requirement
Write down what the instrument must actually do before looking at components:
- Range, against a defined target. "Two kilometres" means nothing without saying against what.
- Target characteristics: size, reflectance, and whether it is diffuse or retro-reflective. A road sign and
a matte-painted vehicle at the same distance are not the same problem.
- Update rate: how many measurements per second the system must produce.
- Atmospheric conditions: clear, haze, rain, dust.
- Envelope: the space the transmitter must fit into, and its mass and power budget if it flies.
2. Work out the returned power
For a diffuse target the return falls with the fourth power of range — twice on the way out and twice on the way
back. Doubling the range needs roughly sixteen times the energy for the same received signal, all else equal.
That single relationship explains most of why long-range systems use large pulse energies and large apertures
together.
Retro-reflective targets behave far more favourably, and a target that returns a specular reflection back down
the beam path can be detected at a range the diffuse calculation would rule out entirely.
3. Add the atmosphere
Transmission depends on wavelength, visibility and range. At 1535 nm and at 905 nm the losses over a given path
differ, and in haze or rain the difference matters. The atmosphere is not a constant to be assumed; it is a
condition to be stated. Why 1535 nm was chosen in the first place
is covered separately.
4. Size the receiver
The return is spread over an area that grows with range. What the receiver collects is set by its aperture, and
what it can detect is set by its sensitivity and noise. A larger aperture gathers more light but costs envelope,
mass and money — usually the harder constraint to relax.
5. Check the margin
Detection needs a signal above the noise by a stated factor, for a stated false-alarm rate. This margin is where
a design either works or fails, and it is the number that should be recorded in the specification, not just the
transmitter's pulse energy.
Where pulse energy changes the answer
With the chain above in mind, pulse energy is the term you can most easily change, and it moves the design in
three ways.
Range. More energy means more returned signal, and because the return falls as the fourth power of range,
the gain in range is gradual. Doubling the energy does not double the range.
Aperture and receiver cost. If the receiver is already fixed — a chosen detector, a fixed aperture — then
the only way to reach further is more energy. Conversely, a larger energy budget can let you use a smaller
aperture, which is often what an airborne payload requires.
Drive current. More energy is not free at the electrical end. The compact models run at 8 to 20 A; the
high-energy models need 80 to 100 A at up to 14 V. If the supply or the driver already exists, that may settle
the energy tier before the optics do.
The constraint that usually decides the wavelength: eye safety
At 1535 nm, light is absorbed in the front of the eye before it can reach the retina, and the energy is spread
through the thickness of the cornea rather than concentrated on a small spot. At 905 nm, a substantial fraction
passes through to the retina.
The practical consequence is that a 1535 nm source can operate at a higher pulse energy within the same
eye-safety class than a shorter-wavelength source. For an instrument used where people may be present — a
surveying site, a vehicle, an aircraft operating over an area — this changes what energy is available to the
design.
The sources in this range are specified as Class 1 at 1535 nm.
Matching energy to application
The table below is the published specification. Every model shares the same 1535 nm wavelength, Class 1
eye safety and TEM00 beam quality, so the choice is made on energy, repetition rate, pulse width and envelope.
| Model | Package tier | Pulse energy | Repetition rate | Pulse width | Dimensions | Weight |
|---|---|---|---|---|---|---|
| MINI-100 | Micro package | ≥100 µJ | 1–10 Hz | 3.5 ns | 14.5×6.3×4.37 mm³ | 2.5 g |
| ER100 | Micro package | ≥100 µJ | 1–10 Hz | 6 ns | 21×8×6.8 mm³ | 7 g |
| ER200 | Compact | ≥200 µJ | 1–10 Hz | 5 ns | 21×8×6.8 mm³ | 7 g |
| ER300 | Compact | ≥300 µJ | 1–10 Hz | 5 ns | 25×8×6.8 mm³ | 8.5 g |
| ER400 | Compact | ≥400 µJ | 1–10 Hz | 6 ns | 35×8×6.8 mm³ | 12 g |
| ER500 | Compact | ≥500 µJ | 1–10 Hz | 6 ns | 35×8×6.8 mm³ | 12 g |
| ER800 | Standard | ≥800 µJ | 1–10 Hz | 7 ns | 40×8×7.5 mm³ | 18 g |
| ER900 | Standard | ≥900 µJ | 1–5 Hz | 7 ns | 40×8×7.5 mm³ | 18 g |
| ER2000 | High energy | ≥2 mJ | 1–5 Hz | 12 ns | 60×25×13.5 mm³ | 105 g |
| ER4000 | High energy | ≥4 mJ | 1–5 Hz | 12 ns | 60×25×13.5 mm³ | 105 g |
| ER8000 | High energy | ≥8 mJ | 1–5 Hz | 13 ns | 110×40×24.5 mm³ | 220 g |
| ER10000 | High energy | ≥10 mJ | 1–5 Hz | 12 ns | 110×40×24.5 mm³ | 220 g |
Short range and dense sensing — 10 to 100 µJ
The MINI-100 is the smallest unit in the range at
14.5×6.3×4.37 mm³ and 2.5 g, with ≥100 µJ. It suits miniature rangefinders and instruments where the envelope
is the binding constraint rather than the range. The ER100 carries the same energy in a
larger package, and draws 8 A rather than the MINI-100's 12 A.
General ranging and mapping — 200 to 500 µJ
The compact tier covers most handheld and vehicle-mounted instruments. The ER400 and
ER500 at ≥400 µJ and ≥500 µJ are the usual starting points for multi-kilometre ranging with a
conventional receiver, and they share a 35×8×6.8 mm³ envelope.
Extended range — 800 µJ to 1 mJ
The ER800 at ≥800 µJ and the ER900 at ≥900 µJ sit in a
40×8×7.5 mm³ package at 18 g. The ER900's repetition rate is 1–5 Hz rather than 1–10 Hz; if update rate matters,
that is the difference to notice.
Long range and remote sensing — 2 to 10 mJ
The high-energy tier runs from the ER2000 at ≥2 mJ to the
ER10000 at ≥10 mJ, in packages from 60×25×13.5 mm³ to 110×40×24.5 mm³. Pulse width is
longer here — 12 to 13 ns — and so is the drive: 80 A for the ER2000, 100 A for the larger two. The article on
pulse width and range resolution covers what the longer pulse costs.
What else to fix before choosing
Three parameters interact with energy and are easy to overlook.
Pulse width sets how close together two returns can be told apart. A 4 ns pulse can resolve targets roughly
half a metre apart; a 12 ns pulse resolves about two metres. If the application needs to separate a vehicle from
the ground behind it, pulse width is a hard constraint, not a secondary one.
Repetition rate sets how many measurements per second the instrument produces, which for a scanning system
determines point density. The high-repetition family —
ER10, ER20, ER40, ER70 — runs from
500 Hz to 5 kHz, but at energies of 10 to 70 µJ. High rate and high energy are not available in the same
package, so one of them has to be the requirement. The
point density article works through the arithmetic.
Drive conditions must be matched. Each model publishes a maximum drive pulse width — 0.3 ms for the ER10 and
ER20, 2.4 ms for the compact tier, 4 ms for the ER2000 and above — and the driver supply must be matched to the
stated voltage and current. Exceeding the drive limit risks the source.
A practical order of work
- State the range against a defined target, with visibility and update rate.
- Work the link budget, and record the margin you need.
- Decide whether pulse width constrains target separation.
- Decide whether repetition rate constrains point density.
- Check what drive current and voltage the supply can provide.
- Only then choose the energy tier, and the envelope that comes with it.
- Confirm operating temperature — most models here are specified −40 °C to +65 °C, and the high-repetition
family −45 °C to +65 °C, but the thermal path in your housing is yours to design.
- Confirm the drive interface against the datasheet before design freeze.
Next steps
The full range with published specification tables is on the
Laser Sources page, and each model page carries its datasheet and a 3D model for mechanical
integration. If your requirement is not covered by a standard model, the customisation scope is described on
For a specific requirement, send the range, target, update rate and envelope through
Contact / RFQ and we will identify the parameters that need to be fixed first.