Aug 25, 2026Translation missing: en.blog.post.reading_time

How to Test Picosecond Laser Energy Stability Before Accepting a Machine

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A picosecond laser energy stability test does more than confirm that one pulse hit the advertised millijoule figure. A factory acceptance test (FAT) evaluates the measurement equipment, the controlled conditions, repeated-shot output, short-term fluctuation, warm-up drift, spot-size and wavelength behaviour, beam shape and cooling stability — with everything traceable to the exact serial number being shipped. Acceptance criteria must be agreed with the supplier before the test runs, not written after the results are seen.

Quick answer: What does a proper energy stability test cover?

Nine things. A calibrated energy meter with a documented calibration date. Multiple pulse-energy readings — not one hero shot. Repeated-shot variation (min, max, mean, spread). Warm-up drift after a documented interval. Actual spot diameter measured, not assumed. Each installed wavelength tested separately. Beam-profile evidence at more than one spot. Cooling status recorded throughout. And a signed serial-level report linking every result to the specific machine serial number leaving the factory.

How to use this guide

This checklist is for distributors, technical buyers, clinic owners and procurement teams evaluating professional picosecond laser machines before shipment or final payment. Every acceptance tolerance should come from the supplier's documented specification and the signed purchase agreement — not from a generic blog figure.

Picosecond FAT: Test Items, Evidence and Pass/Fail Basis

The framework below identifies each test item, the evidence recorded, why it matters, and the source that defines the pass/fail basis.

PICOSECOND ENERGY-STABILITY FAT — SUMMARY

TEST ITEM	WHAT TO RECORD	WHY IT MATTERS	PASS/FAIL BASIS
Energy meter	Model, sensor, calibration date	Establishes measurement credibility	Approved meter and range
Pulse energy	Multiple readings at defined conditions	Verifies actual output	Supplier specification
Repeated-shot variation	Min, max, mean, spread	Shows stability	Agreed tolerance
Warm-up drift	Energy against elapsed time	Detects thermal drift	Agreed tolerance
Spot size	Actual measured diameter	Needed for fluence calculation	Specification tolerance
Wavelength	1064/532 nm or installed options	Confirms configuration	Purchase order
Beam profile	Shape and uniformity report	Finds hotspots and asymmetry	Agreed acceptance criterion
Cooling	Temperature and any alarms	Tests thermal stability	No unresolved fault
Serial report	Machine ID linked to results	Ties evidence to the shipped unit	Required documentation

Acceptance limits are set from the supplier's written specification and the purchase agreement — not from a universal figure. Agree every tolerance before the test runs.

What Does Picosecond Laser Energy Stability Actually Mean?

Three properties get confused in supplier conversations. All three must be evaluated separately.

Accuracy = does measured energy match the expected nominal value?

Repeatability = do repeated pulses produce similar energy readings?

Drift = does output change as the machine warms or runs longer?

ACCURACY	REPEATABILITY
Closeness to the expected value	Closeness of repeated readings to each other
One reading can look accurate	Requires multiple readings
Does not prove stability	Does not automatically prove calibration
Compare to specification	Compare shot-to-shot variation

A machine can be repeatable but incorrectly calibrated, or accurate on one pulse but unstable across many pulses. Any FAT that stops after one impressive reading has verified neither.

Factory Acceptance Test vs Site Acceptance Test

A factory acceptance test (FAT) runs before shipment; a site acceptance test (SAT) runs after installation. Both are needed — FAT prevents the wrong configuration shipping, SAT catches transport and installation problems.

FACTORY ACCEPTANCE TEST (FAT)	SITE ACCEPTANCE TEST (SAT)
Before shipment	After installation
Factory environment	Clinic environment
Prevents wrong-configuration shipping	Finds shipping and setup problems
Supports final-payment decision	Supports clinical handover
Supplier normally performs, buyer witnesses	Buyer or service team verifies

Define Pass/Fail Criteria Before the Test Runs

Every acceptance parameter must be written and agreed before the machine is switched on: wavelength, spot size, nominal energy, allowed variation, repetition rate, warm-up requirement, test duration and beam criteria. The most common way FATs fail buyers is when tolerance is set after the readings are in.

Do not let the supplier change acceptable variation after seeing results
Do not discard a bad reading without a documented reason
Do not retest at easier settings to obtain a pass
Do not move the measurement location partway through the sequence

Structure the acceptance document with six columns per parameter: parameter, target, tolerance, test method, required evidence, pass/fail.

Calibrated Energy Meter vs Machine Display

The machine display shows the programmed setpoint against stored calibration — it cannot verify itself. An external calibrated energy meter provides the physical measurement the FAT is built on.

MACHINE DISPLAY	CALIBRATED ENERGY METER
System setpoint	Independent measurement
Useful during normal operation	Useful for acceptance
Depends on machine calibration	Has separate calibration
Cannot verify itself	Provides external evidence

Meter suitability

Record meter manufacturer, model, sensor head, wavelength range, energy range, calibration status and serial number. Test equipment must tolerate the pulse energy, peak power, wavelength and repetition rate being measured. Do not improvise neutral-density filters or attenuators without a validated setup.

Set Up a Repeatable Test Condition

A useful FAT requires repeatable geometry, not hand-held measurements that change from pulse to pulse. Record four categories before the first shot.

Environment: room temperature, machine location, airflow around cooling vents, supply voltage where relevant.

Machine state: cold or warmed up, coolant temperature and status, error and warning state, handpiece or delivery system.

Laser setting: wavelength, spot size, energy setting, repetition rate, pulse mode.

Geometry: measurement distance, handpiece orientation, sensor position, spot location on the sensor.

Cold-Start Energy vs Warm-System Energy

A cold-start reading is the initial baseline. A warm-system reading — taken after sustained operation at the tested settings — reveals the thermal behaviour that determines real clinic performance. A test that stops after cold-start alone has skipped the harder half.

COLD-START ENERGY	WARM-SYSTEM ENERGY
Initial condition	Thermally loaded condition
Easy to demonstrate	More representative of sustained use
May look stable	Can expose drift
Does not test cooling capacity	Tests thermal interaction

Short-Term Fluctuation vs Long-Term Drift

Fluctuation is rapid shot-to-shot variation; drift is a gradual movement of the mean over time. The two need different metrics: fluctuation is captured by shot-to-shot spread, drift by a time-series trend.

FLUCTUATION	DRIFT
Fast, shot-to-shot changes	Slow change over minutes
May require statistical spread	Requires time-series trend
Can average around the same mean	The mean itself moves
Missed by cold-start test alone	Missed by short sequences

Number of Shots and Repeated-Shot Variance

There is no universal number of shots. The sequence length is set in the acceptance document based on the supplier specification and the operating configuration. A workable framework: baseline sequence, sustained sequence, warm sequence — each documented separately for each wavelength, spot size and repetition rate.

Do not cherry-pick readings

The raw sequence should be retained in full. If any reading is invalidated, state why in writing, keep the original in the raw data, and identify its replacement.

Base statistics and variation metrics

Record minimum, maximum, mean and range. Add a variation metric — range relative to mean, standard deviation, or coefficient of variation — and use it consistently.

Mean energy = sum of measured pulses ÷ number of pulses recorded.

Coefficient of variation = standard deviation ÷ mean, expressed as a percentage. Compare to the supplier's written stability specification — do not adopt a universal figure from an unrelated product.

SUPPLIER SPECIFICATION	TEST RESULT
Contractual or quoted stability	Measured sequence
Defines the acceptance limit	Shows whether the limit is met
Must state test conditions	Must use comparable conditions

Nominal Energy vs Delivered Energy

Nominal energy is what the interface or specification claims. Delivered energy is what reaches the measurement plane. Ask the supplier where its stated energy is measured — inside the laser cavity, before delivery optics, after the articulated arm or at the treatment exit. The picosecond laser buyer's guide recommends requesting energy at the handpiece and at each spot size.

1064 nm vs 532 nm Energy Testing

Each installed wavelength must be tested separately. Stability at 1064 nm does not prove stability at 532 nm — the wavelengths use different detector settings, and where 532 nm is produced by frequency conversion the output characteristics may differ.

1064 NM TEST	532 NM TEST
Separate energy baseline	Separate energy baseline
Separate detector compatibility	Separate detector compatibility
Does not validate 532 nm	Does not validate 1064 nm
Record independently	Record independently

The C19 laser system product page publishes different maximum energy values for 1064 nm and 532 nm — a working example of why each wavelength needs its own test record and its own agreed tolerance.

Spot Size, Diameter Verification and Beam Uniformity

Energy stability at one spot does not prove stability at other spots. Prioritise smallest practical, typical operating and largest advertised spot. Fluence equals energy divided by spot area — an incorrect spot diameter changes calculated fluence even when the meter reading is correct, which is why diameter must be measured, not assumed.

SPOT-SIZE ENERGY-STABILITY WORKSHEET

SPOT SIZE	NOMINAL ENERGY	MEAN MEASURED	VARIATION	MEASURED DIAMETER	RESULT
Small	Record	Record	Calculate	Measure	Pass/fail
Medium	Record	Record	Calculate	Measure	Pass/fail
Large	Record	Record	Calculate	Measure	Pass/fail

Functional worksheet — the buyer records actual values into each cell during the FAT. The C16 and C19 pages advertise spot ranges from 2–10 mm, so "Small / Medium / Large" for those platforms typically means 2 mm, a mid-range spot, and 10 mm.

Spot diameter vs beam uniformity

SPOT DIAMETER	BEAM PROFILE
Measures physical footprint	Measures energy distribution
Can be correct despite a hotspot	Shows centre-to-edge behaviour
Needed for fluence	Needed for uniformity
Simple dimensional parameter	Optical-quality parameter

A visual spot on a target card shows gross centring but cannot quantify uniformity or resolve small hotspots. Where uniformity is part of the acceptance criteria, request a beam-profiler report — a photograph or burn mark is not a substitute for quantitative data.

Repetition Rate and Cooling Stability

Low-rate energy is a baseline. Higher rates test capacitor recharge, thermal loading and cooling capacity. Because the C16 and C19 platforms advertise operation up to 10 Hz, the FAT should document behaviour at the repetition rates in the purchase specification, not only at the easiest setting.

LOW HZ TEST	HIGH HZ TEST
Easier thermal condition	Higher sustained load
Useful baseline	Tests clinic-speed configuration
May maximise pulse energy	Energy may behave differently
Does not prove high-rate stability	More demanding FAT condition

Record cooling during the test

Track coolant temperature, machine temperature where displayed, fan and pump status, flow warnings and thermal warnings throughout the sequence. If output becomes unstable only as the machine heats, a cold-start test will miss it — which is exactly why the FAT includes a warm-system stage.

Factory Demo Video vs Buyer-Grade FAT Evidence

A promotional video shows the machine firing, a meter display and one energy result. Buyer-grade FAT evidence documents compliance.

PROMOTIONAL DEMO VIDEO	BUYER-GRADE FAT EVIDENCE
Shows capability	Documents compliance
Often edited	Continuous sequence preferred
May omit conditions	Conditions visible throughout
One impressive reading	Repeated dataset

What the FAT video and report should show

The video should keep machine model, serial number, test instrument, calibration label, wavelength, spot size, energy setting and repetition rate visible throughout the sequence — with cold-start and warm-system readings recorded in the same take. The written report ties every result back to the specific serial number being shipped. The LEFIS certifications and compliance page describes pre-shipment performance testing and batch traceability, which is the basis for insisting on serial-level FAT evidence.

C16 vs C19: The FAT Fields to Populate

The two LEFIS platforms illustrate what a scoped FAT looks like on a real Q-switched Nd:YAG picosecond-category system. This is not a "which is better" comparison — both should be tested against the same acceptance framework, at their own published specifications.

C16 test fields

The C16 laser system page publishes 1064/532 nm, up to 10 Hz, 2–10 mm spots and closed-loop water-plus-air cooling. FAT questions: what energy does the shipped unit measure at each wavelength? How stable is repeated output? Does stability change across spot sizes? What happens after warm-up? What is the result at higher Hz?

C19 test fields

The C19 laser system page publishes 1064 nm up to 1000 mJ, 532 nm up to 500 mJ, 2–10 mm spots, up to 10 Hz and liquid-plus-forced-air cooling. Populate the same FAT questions per wavelength, using the C19's own published maximum energy values as the supplier specification.

Pass/Fail Report Template

A functional worksheet for the buyer to complete during the FAT. Every Requirement column is populated from the supplier's written specification agreed before testing; Measured result, Pass/Fail and Evidence file columns are completed during the test itself.

Machine and equipment identification

Machine: manufacturer, model, serial number, software version, manufacture date
Measurement equipment: energy meter, sensor head, serial number, calibration date
Test conditions: room temperature, cooling status, warm-up time, wavelength, spot size, repetition rate, nominal energy

FAT RESULTS TABLE

TEST	REQUIREMENT	MEASURED RESULT	PASS/FAIL	EVIDENCE FILE
1064 nm energy	Supplier spec	Record	P/F	File ref
532 nm energy	Supplier spec	Record	P/F	File ref
Repeated-shot variation	Agreed limit	Calculate	P/F	File ref
Warm-up drift	Agreed limit	Calculate	P/F	File ref
Spot diameter	Supplier spec	Measure	P/F	File ref
Beam uniformity	Agreed criterion	Record	P/F	File ref
High-Hz stability	Agreed criterion	Record	P/F	File ref
Cooling test	No unresolved fault	Record	P/F	File ref

Requirement column: populated from the supplier's written specification before the test. Measured result and Pass/Fail: completed during the test. Evidence file: references the video, screenshot or raw data supporting each row.

Retest Triggers and Stop-Acceptance Conditions

Automatically retest when

A sequence should be repeated — with the reason documented — if any of the following occur: meter overload or sensor saturation, machine warning, accidental geometry change, spot-size or wavelength change, cooling fault, handpiece movement, unexplained outlier, or sequence interruption. Retests must document why the first sequence was invalidated rather than silently replacing poor results with better ones.

Hold acceptance pending investigation when

Measured output falls outside the agreed specification
Repeated instability exceeds the agreed tolerance
Warm-up drift persists across a full sequence
Wavelength configuration or spot dimensions do not match the purchase order
Severe beam asymmetry or hotspot is present
Recurring cooling alarms cannot be cleared
Output drops unexplained at the rated repetition rate
Serial number, meter calibration or factory test record is missing, mismatched or expired

Final Picosecond Laser Energy Stability Test Checklist

Before accepting the machine — or releasing final payment — confirm the FAT has:

confirmed the machine serial number and defined pass/fail tolerance from the supplier's written specification
verified energy-meter suitability, sensor range and current calibration status
recorded environmental conditions, cooling status, wavelength, spot, energy and Hz per sequence
recorded cold-start readings, then repeated readings after warm-up
calculated mean, variation and warm-up drift for each configuration tested
verified actual spot diameter and inspected beam uniformity
tested each installed wavelength separately and the applicable higher repetition rates
recorded cooling behaviour throughout the sequence
saved raw readings and continuous FAT video
completed a serial-level pass/fail report against pre-agreed criteria

Request a Factory Acceptance Video and Energy Test Report

One pulse does not establish stability. Nominal energy, measured energy and stability are three separate properties — all three should be evaluated at every installed wavelength, at more than one spot size, at more than one repetition rate, and both cold and warm — with raw data preserved and every result tied to the specific serial number being shipped.

Compare the LEFIS picosecond laser machines and use the laser technical support page to request the continuous FAT video, the serial-level energy test report and pass/fail documentation for the exact configuration on the quotation. Confirm acceptance tolerance and evidence format in writing before the test runs.

FAQs

What is a picosecond laser energy stability test?

A factory acceptance test that verifies measured pulse energy at the handpiece, with calibrated equipment, at defined wavelength, spot size and repetition rate, across repeated readings both cold and warm. The result is compared against the supplier's written specification agreed before testing.

How do you measure picosecond laser pulse energy?

With a calibrated energy meter and a sensor rated for the wavelength, pulse energy, peak power and repetition rate. Record meter and sensor model, serial and calibration date; hold spot size, distance, orientation and machine state constant; take multiple readings, not one hero shot.

How many pulses should be tested during factory acceptance?

There is no universal number. Set sequence length in the acceptance document based on the supplier specification and configuration. A workable framework: baseline sequence, sustained sequence, warm sequence — each recorded separately per wavelength, spot size and repetition rate.

What is the difference between laser fluctuation and drift?

Fluctuation is fast shot-to-shot variation. Drift is a slow change of the mean over time — upward, downward or cyclic. Fluctuation is captured with statistical spread; drift with a time-series trend. A short cold-start test can pass both while missing them entirely.

Why should picosecond laser energy be tested after warm-up?

Because thermal drift, cooling weakness and alignment sensitivity only appear once the machine has been running at operating load. Cold-start verifies the first pulse; warm-system verifies the machine can maintain performance across a treatment session.

Should 532 nm and 1064 nm energy be tested separately?

Yes. Stability at one wavelength does not prove stability at the other. Different detector settings apply, and where 532 nm is produced by frequency conversion the characteristics can differ. Record independent baselines, means, variations and results per wavelength.

Does spot size affect picosecond laser energy testing?

Yes. Fluence equals energy divided by spot area — the same pulse energy at 2 mm produces very different fluence from 10 mm. Most systems do not maintain headline mJ at every listed spot. Test smallest practical, typical operating and largest advertised, and verify actual diameter.

How do you check whether a laser spot is uniform?

With a beam profiler producing quantitative centre-to-edge distribution data at more than one spot size. Burn paper or a target-card mark shows gross centring but cannot quantify uniformity or resolve small hotspots. Agree the uniformity acceptance criterion in writing before the FAT.

What should a picosecond laser factory acceptance report include?

Machine model, serial, software and manufacture date; meter, sensor, serial and calibration date; environmental and cooling conditions; wavelength, spot, Hz and nominal energy per sequence; raw readings, calculated statistics, pass/fail against pre-agreed limits, and file references for video, screenshots and logs.

What happens if a laser fails an energy stability test?

Hold acceptance pending investigation — do not condemn the machine automatically. Common causes: incorrect meter or wavelength setting, geometry change during the sequence, cooling fault, incorrect spot size, or drift after warm-up. Document the failed criterion, retest with reason recorded, and escalate before releasing final payment.