Development of an Accurate Laser Power Testing Kit for Safety

Assessment of Commercial Laser Pointers in Thailand

Kanokwan Nontapot and Narat Rujirat

Electrical Metrology Department, National Institute of Metrology, Pathumthani, Thailand

Keywords: Laser Pointers, Laser Power, Laser Safety Level, Measurement Uncertainty.

Abstract: Recent advances in laser technology have enabled low-cost, more powerful, and more visible wavelengths

of laser pointers. Large numbers of these high power lasers have found their way into people’s lives and are

being used by people who may be unaware of potential eye injury, resulting in increased reports of retinal

injuries. Therefore, many countries have issued restrictions or regulations, on the power limit of laser

pointers used for demonstration purposes. At present, there are none of these regulations on the sale and use

of laser pointers in Thailand. In this research, an accurate, inexpensive, user friendly, laser pointer power

testing kit will be built for the measurement of optical power emitted from handheld lasers. The setup

consists of a thermopile power meter, optical bandpass filters, lens mounts, lens tube, and iris. Output power

of about 20 laser pointers randomly purchased from various sources will be determined, including

evaluation of measurement uncertainty. The safety level with respect to the limits imposed by the US Code

of Federal regulations will be also discussed.

1 INTRODUCTION

Up-to-date, handheld lasers such as laser pen or laser

pointers have been widely used around the world.

The most common ones are laser pointers used in

presentations and demonstrations, especially in

classrooms. Some other uses of laser pointers are for

toys, hobbies and entertainments, such as for special

effects in concerts or in nightclubs. Due to rapid

advances in laser technology, laser pointers have

become cheaper, more affordable, and have more

colors available. Not only the red He-Ne laser

pointers that are cheap and popular, the green and

violet, have become more available and most

recently, blue laser pointers are now the new trend.

Apart from the variety of colors, the power level of

those lasers is also varied. From safe level of 1mW

to very dangerous 1000mW can be easily purchased

on the market despite many countries issuing the

legal limit of handheld laser pointer at no more than

5mW (such as in the US) or as low as 1 mW (such

as in the UK). Easily access of powerful laser

pointers resulted in increasing report of eyes injury

around the world (Wong, et al., 2007, Wyrsch, et al.,

2010, Ziahosseini, et al., 2010). In 2008, the

Australian government restricted the sale and

importation of some laser items and also banned the

importation of laser pointers that emit the power

more than 1 mW, due to several cases of coordinated

attacks on passenger jets in Sydney (Sydney

Morning Herald, 2008). In 2010, the Federal Office

of Metrology in Switzerland randomly tested laser

pointers and found that a high percentage of laser

pointers were not in compliance with the regulation

(Blattner , 2011). More recently, researchers at the

National Institute of Standards and Technology

(NIST, USA) tested 23 laser pointers and found that

44 percent of red lasers pointers and 90 percent of

green laser pointers were not in compliance with

federal safety regulations (Joshua and Marla, 2013).

In Thailand, there is no rule or regulation

regarding the sale or importation of laser devices.

Laser pointers or laser gadgets of all colors and

power range, from less than mw to many watts can

be easily purchased in the stores and online. Misuse

of these devices can be very dangerous, thus it is

important to assess the power output of these laser

pointers to determine both their hazard level and

their class labels.

Even though there are many reports of green

laser hazards published in scientific journals and the

media, no report of violet laser pointer hazards has

been published so far. In this work, 19 laser pointers

of 3 different colors, red, green, and violet,

Nontapot, K. and Rujirat, N.

Development of an Accurate Laser Power Testing Kit for Safety Assessment of Commercial Laser Pointers in Thailand.

DOI: 10.5220/0005691300260030

In Proceedings of the 4th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2016), pages 28-32

ISBN: 978-989-758-174-8

randomly purchased from stores and online, were

accurately measured and their hazard level

determined. At the present time, there is no

regulation of the sale or importation of laser devices

in Thailand. In this work, the hazard level of laser

pointers were determined according to the The US

Code of Federal Regulations

(CFR, 2012) which

limits commercial class IIIa/3R lasers to 5 milliwatts

(mW) and no more than 1 mW for dangerous IR.

1.1 Laser Class and Safety

The American Standard for the Safe Use of Lasers

(ANSI 136.1-2007) classifies lasers into 4 classes,

according to their hazard level. Table 1 illustrates

the laser hazardous level.

Table 1: Laser classification under ANSI Z136.1-2007.

Class Hazard level

Class 1 Non-hazardous level under normal use

Class 2

Non-hazardous level under normal use,

for visible laser only, laser power < 1

Class 3R

Potentially hazardous level if viewing

for extend period of time, includes both

visible and non-visible lasers, laser

power < 5mW

Class 3B

Hazardous to skin and eyes, , includes

both visible and non-visible lasers,

laser power < 500mW

Class 4

Very hazardous, laser power >500 mW,

can burn skin

1.2 Laser Pointer Technology

Recent advance in laser technology made laser

pointer in the markets become cheaper, smaller, and

more powerful. Modern red laser pointers are

constructed from vertical-cavity surface-emitting

laser (VCSEL) diodes technology, emitting deep red

light near 650 nm, which are the least expensive red

laser pointers. Newer version red laser pointers (but

slightly more expensive ones) emit red-orange light

at 635 nm, which is more visible to human eyes.

Green laser pointers, are now the most popular since

human eyes are most sensitive to the green region

of the spectrum at low power. Green lasers are

DPSS lasers (or so called DPSSFD for "diode

pumped solid state frequency-doubled"). The green

light is indirectly generated from

using infrared AlGaAs laser diode operating at

808 nm to pumps a Nd:YVO4 or Nd:YAG crystal.

The crystal then emits laser light in the IR region at

1064 nm. Second harmonic generation at the KTP

crystal generate the green laser light at 532 nm. All

of the light with 3 different wavelengths are then

focused and emitted the green color. Since the

emitting light includes both IR and VIS, high quality

green laser pointer must be equipped with a filter

that can block or allow IR wavelength (both 808 nm

and 1064 nm) to transmit with lowest level of power

as possible (less than 0.63 mW at 808 nm and 1.92

mW at 1064 nm), referred to ANSI (ANZI, 2007)

and IEC (IEC, 2007).

Violet lasers emitting a violet light at 405 nm are

constructed from GaN (gallium nitride)

semiconductors. This type of laser directly emits

405 nm without frequency doubling as the DPSS

green laser, thus emitting none of the dangerous IR

emission but can emit high power in excess of the

CFR limit.

2 EXPERIMENTAL DESIGN

The goal of the research is to conveniently, safely,

and accurately measure the laser power output of the

laser pointers without expensive parts. The apparatus

must be able to measure all of the power emitting

from red, green and violet laser pointers, both in

visible and IR regions.

2.1 Measurement Apparatus

The apparatus is built concerning the safety of

operation with accurate and repeatable measurement

results. The design is inspired from Joshua’s

prototype (Joshua and Marla, 2013), which is

composed of a power meter, a selectable filter

wheel, a lens tube, an iris, self-centering lens

mounts, and laser pointer under tested, as shown in

figure 1.

Figure 1: Measurement apparatus. A laser pointer (A) is

mounted using 2 self-centering lens mounts (B) for hand

free, and repeatable measurement. The adjustable iris (C)

closed around the laser pointer and the lens tube (D) cover

the laser path to protect operator from laser light.

Bandpass filters are mounted in a selectable filter wheel

(E). A power meter (F) reads the power output of the laser

at the other end of the filter.

Development of an Accurate Laser Power Testing Kit for Safety Assessment of Commercial Laser Pointers in Thailand

2.2 Power Meter

In this work, the thermopile detector was used, due

to its spectrally flat responsivity, low cost, and ease

of operation. The spectral range of the detector

(Model 3A-P, Ophir) is 0.15-6 um, covering a power

range of 60 µW to 3 W. To determine the calibration

factor and uncertainty, standard calibration

procedures of laser power detector at National

Institute of Metrology (Thailand) were followed.

The power meter was calibrated by direct

comparison with laser power reference standard,

which was directly compared with the laser

Calorimeter (traceable to SI units). The calibration

results are discussed in Appendix.

2.3 Band Pass Filter

The DPSS green laser pointers emit the laser not

only at green visible (532 nm) but at wavelength

both 808 nm (the pump) and 1064 nm (the

fundamental). The bandpass filters used in this

measurement were the 800 ± 8 nm, FWHM = 40 ± 8

nm, and 1064 ± 2 nm, FWHM = 10 ± 2 nm. The

transmission was tested with a Nd:YAG laser at

1064 nm and 532 nm, for the 1064 nm bandpass

filter. The transmission of the 800 nm filter was also

tested with the Nd:YAG laser and assumed to have

the same uncertainty.

The calibration results are

discussed in Appendix.

3 MEASUREMENTS AND

RESULTS

For red and violet laser pointers, which are single

wavelength lasers, no bandpass filters were used.

The power is

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Where C

is the calibration factor of the power

meter, obtained from calibration. For each

measurement, the laser was energized for 30 s and

the output power was recorded using the maximum

power reading of the power meter. Measurement

results are shown in figures 2-4.

A total of 19 lasers pointers (12 red, 4 green, and

3 violet) were randomly purchased from Thailand

stores and online markets. All of the pointers were

advertised as laser pointers for demonstration

purposes and all are in class 3R or below. In the red

laser samples, 3 out of 12 laser pointers emitted the

power of more than 5 mW, in excess of the CFR

limits. For green laser pointers, 2 out of 4 pointers

emitted the power in excess of the CFR limits (Class

3R visible accessible emission limit (AEL) and

Class 1IR AEL). For visible green wavelength, one

emitted the power at ~70 mW, and another at ~ 20

mW. At 1064 nm, one emitted the IR power at ~ 10

mW and another at ~20 mW. At 808 nm, both lasers

emitted the power at ~ 1.5 mW. For blue laser

pointers, all with the < 5 mW label, the measurement

results revealed that all the 3 pointers emitted the

power in excess of the CFR limit.

Figure 2: Measured output power of 12 red laser pointers.

The horizontal dashed line represents the class 3R visible

AEL limit of 5 mW. 3 out of 12 red pointers emitted

power in excess of the CFR limits.

Figure 3: Measured output power of 4 green laser pointers.

The horizontal dashed line represents the class 3R visible

AEL limit of 5 mW. 2 out of 4 green pointers emitted

power in excess of the CFR limits for both visible and IR

wavelengths.

PHOTOPTICS 2016 - 4th International Conference on Photonics, Optics and Laser Technology

Figure 4: Measured output power of 3 violet laser pointers.

The horizontal dashed line represents the class 3R visible

AEL limit of 5 mW. All of the violet pointers emitted

power in excess of the CFR limits.

4 CONCLUSIONS

Power outputs of 19 laser pointers of 3 different

colors (red, green and violet) randomly purchased

from Thai markets, were accurately measured to

verify their compliance with the guidelines of US

CFR and ANSI. The output power of measurement

set up has an uncertainty of 1%. The uncertainty was

determined from the calibration of the power

detector and the bandpass filter. The calibration of

power detector was performed using standard

practice of National Institute of Metrology

(Thailand) laser power calibration and is traceable to

SI units. The bandpass filter were calibrated

following the procedure given by Joshua (Joshua

and Marla, 2013). The measuring results including

the measurement uncertainty of 1 % show that

majority of red laser pointers are in compliance with

the CFR regulations while 50% of green laser

pointers were exceeded the class 3R limit at both

visible and IR wavelengths. For violet laser pointer

measurement, all of the pointers were non-

compliance with CFR. This work provides the first

and the most accurate results of the laser pointers

safety assessment level in Thailand. At the present,

there is no rule or regulation regarding the sale or

importation of laser devices in Thailand. The results

could be used as guidance for the Thai (or similar

countries) regulation and standardization bodies,

when issuing regulations regarding the sale or

importation of laser devices. The apparatus could

be used by any institutions, universities,

organizations and companies, to determine the safety

level of their laser pointers.

ACKNOWLEDGEMENTS

This work is supported by the new researcher

scholarship of CSTS, MOST project, which is

sponsored by the Coordinating Center for Thai

Government Science and Technology Scholarship

Students (CSTS), National Science and Technology

Development Agency (NSTDA).

REFERENCES

Wong, R., Sim, D., Rajendram, R., and Menon, G., 2007.

Class 3A laser pointer-induced retinal damage

captured on optical coherence tomography. In Acta

Opthal mol. Scand. 85227–8.

Wyrsch, S., Baenninger, P. B.., and Schmid, M K., 2010.

Retinal injuries from a handheld laser pointer. In N.

Engl. J. Med. 3631089-91.

Ziahosseini, K., Doris, J. P., and Turner, G. S., 2010.

Maculopathy from handheld green diode laser pointer.

In BMJ 340c2982.

Laser pointers restricted after attacks. Sydney Morning

Herald. 2008-04-06. Retrieved 2008-04-06.

Blattner, P., 2011. The underrated hazard potential of laser

pointers. In METinfo18.

Joshua, H., Marla, D., 2013. Accurate, inexpensive testing

of laser pointer for safe operation. In Meas. Sci.

Technol. 24(2013) 045202 (7pp).

CFR 2012 Code of Federal Regulations Title 21. Food and

Drug; Part 1040: Performance Standards for Light-

Emitting Products; Section 1040.10 Laser Products

(US 21 CFR 1040.10).

ANSI 2007 American National Standard for the Safe Use

of Lasers (Orlando: Laser Institute of America) ANSI

Z136.1.

IEC 2007 Safety of Laser Products. Part 1: Equipment

classification and requirements (International

Electrotechnical Commission) EN 60825-1 ed.2.

Taylor, N., Kuyatt, C., 1994. Guidelines for Evaluating

and Expressing the Uncertainty of NIST Measurement

Results, NIST technical Note 1297.

APPENDIX

The uncertainty of the measurement were estimated

following guideline from Taylor and Kuyatt (Taylor

and Kuyatt, 1994). In this work, the estimated total

uncertainty, u



, of the system is











u





(A.1)

where u



is the uncertainty of the power detector

and u



 is the uncertainty of the bandpass filter.

The uncertainty of the power detector is

Development of an Accurate Laser Power Testing Kit for Safety Assessment of Commercial Laser Pointers in Thailand

determined by calibration with laser power meter

reference standard, which was directly compared

with the laser Calorimeter (traceable to SI units).

The calibration was performed at wavelength 633

nm, 515 nm and 488 nm. The calibration results are

shown in table 2.

The uncertainties of the bandpass filters were

estimated from transmission calibration with a

Nd:YAG laser at 1064 nm and 532 nm. For the 1064

nm bandpass filter, the transmission value is the

ratio of the laser power reading on the standard

pyroelectric detector with and without the filter. The

calibration results are shown in table 3. For the 800

nm filter, the transmission at 1064 nm and 532 nm

were tested. The calibration results are shown in

table 3.

Using (A.1), the total uncertainty of the system is

1%.

Table 2: Power detector calibration results.

Wavelength

(nm)

Power

Calibration

Factor, 



Uncertainty,





633

1 mw 1.015 0.6%

3 mw 1.012 0.6%

515

5 mW 1.025 0.9%

10 mW 1.025 0.9%

488 5 mW 1.009 0.9%

Table 3: Bandpass filters calibration results.

Filter

center

wavelength

(nm)

Laser

wavelength

Transmission

Uncertainty, 



800

532

1064

0.00

1064

532 0.00 -

1064 84.92% 0.1 %

PHOTOPTICS 2016 - 4th International Conference on Photonics, Optics and Laser Technology