ARL-TN-0736 ● FEB 2016

US Army Research Laboratory

Safe Operation and Alignment of the Variable

Pulse Width Laser at the US Army Research 

Laboratory 

by Eric S Collins and Jennifer L Gottfried

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ARL-TN-0736 ● FEB 2016

US Army Research Laboratory

Safe Operation and Alignment of the Variable

Pulse Width Laser at the US Army Research 

Laboratory 

by Jennifer L Gottfried

Weapons and Materials Research Directorate, ARL

Eric S Collins 

Oak Ridge Associated Universities, Oak Ridge, TN

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February 2016

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Technical Note

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July 2014–December 2015

4. TITLE AND SUBTITLE

Safe Operation and Alignment of the Variable-Pulse Width Laser at the US 

Army Research Laboratory 

5a. CONTRACT NUMBER

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6. AUTHOR(S)

Eric S Collins and Jennifer L Gottfried

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622618H80

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US Army Research Laboratory

ATTN: RDRL-WML-B

Aberdeen Proving Ground, MD 5069

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ARL-TN-0736

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

The variable pulse width laser at the US Army Research Laboratory can output a maximum of more than 5 J per pulse at pulse 

widths between 50 μs to 10 ms. Maximum energy output is only achieved by proper alignment and laser operation. This report 

provides tips for safe operation to avoid damage to parts within the laser and provides details of a technique to align the variable

pulse width laser that are not included in the operator’s manual. 

15. SUBJECT TERMS

pulse width, laser energy, laser alignment, peak power, laser operation

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OF ABSTRACT

UU

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16

19a. NAME OF RESPONSIBLE PERSON

Jennifer L Gottfried

a. REPORT

Unclassified

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410-278-7573

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Contents

List of Figures iv

List of Tables iv

Acknowledgments v

1. Introduction 1

2. Energy Output of the Variable Pulse Width Laser 1

3. Operation of the Variable Pulse Width Laser 2

4. Precautions for Using the Variable Pulse Width Laser 3

5. Alignment of the Variable Pulse Width Laser 4

6. Conclusion 5

7. References 6

Distribution List 7
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List of Figures

Fig. 1 Comparison of energy output of variable pulse width laser at its new 

and original state (approximately November 2002) and at its current 

state (December 2015)...........................................................................1

Fig. 2 Measured energy and peak power range of the variable pulse width 

laser........................................................................................................2

Fig. 3 Setup for alignment of variable pulse width laser .................................4

List of Tables

Table Replacement parts for the items in the variable pulse width laser head.....3
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Acknowledgments

The authors gratefully acknowledge Jeffrey B Morris (US Army Research 

Laboratory [ARL]) for introducing and assisting with the alignment technique and 

Scott Hamlin (MegaWatt Lasers) for providing details for laser parts and assembly. 

Eric Collins was supported in part by an appointment to the ARL Postdoctoral 

Fellowship Program administered by the Oak Ridge Associated Universities.

Disclaimer: The authors of this report are not responsible for personal injury or 

property damage when operating or aligning the variable pulse width laser. 
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1. Introduction

The variable pulse width laser at the US Army Research Laboratory is an ND:YAG 

laser from MegaWatt Lasers (Model #R5X75-01) with a 1,064-nm wavelength. A 

flashlamp controller with an external capacitor box from Analog Modules (Model 

#8800V-334) is used to control the stored voltage and pulse width setting to adjust 

the energy output of the variable pulse width laser. The capacitors store voltages up 

to 700 V, and the laser has a pulse width range between 50 μs and 

10 ms. Research in the Laser Ignition in Guns, Howitzers and Tanks program in the 

1990’s featured a variable pulse width glass laser,

1–4 and the variable pulse width 

ND:YAG laser used in this study was previously used for research in the US Army 

Environmental Quality Basic Research and Development program.

5,6 It has recently 

been revived for use in a new laser ignition project.

7,8

2. Energy Output of the Variable Pulse Width Laser

Measured energy output data was acquired from the initial installation of the laser 

in November of 20029 and was compared with the laser output measured on 

4 December 2015 (Fig. 1). At a 5-ms pulse width, the original and current measured 

energy outputs were the same at lower voltage levels, and the difference between 

the 2 increased to only 3.5% at the higher voltage levels. 

Fig. 1 Comparison of energy output of variable pulse width laser at its new and original 

state (approximately November 2002) and at its current state (December 2015)
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The measured energy (Fig. 2A) and the peak power (Fig. 2B) with respect to 

pulse width are shown in Fig. 2 (as of 4 December 2015). Figure 2A shows that

the maximum energy increased as the pulse width increased until 2.6 ms, at which 

point the energy decreased as the pulse width continued to increase. The 

maximum measured energy was 7.7 J at 2.6 ms. The peak power of each pulse 

was calculated by dividing the energy by the pulse width. The peak power 

increased as the stored voltage increased from 200 to 700 V. 

Fig. 2 Measured energy and peak power range of the variable pulse width laser

3. Operation of the Variable Pulse Width Laser

To operate the variable pulse width laser, turn the key switch to “ON” and wait for 

the 10-s audible delay period. From the main menu, press “D” to verify that the 

stored lamp parameters match the desired flashlamp operating parameters. Then go 

back to the main menu and press “B” to select the desired pulse rate mode and press 
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the letter corresponding to the desired mode, and then press the arrow up key to 

change that mode to “ON”. Press “A” to change the pulse rate if necessary. From 

the main menu, a preview of the laser settings can be displayed by pressing the 

“Previous Menu” key. In the Preview Menu window, the desired voltage and pulse 

width can be inputted by pressing “B”. 

Press “RUN” to enable the system high voltage and wait a few seconds until the 

system has been fully charged and the display reads “HV fully charged...laser 

paused...press RUN to fire”. When RUN is pressed again, the laser will fire, and 

the display will read “Laser active...Press ‘RUN’ to pause”. When RUN is pressed 

again, the laser will stop firing but the charger will remain enabled. Pressing the 

RUN button will continue to toggle between the fire and pause modes. Pressing the 

“STOP” button will stop the laser and disable the charger. For more details on 

operating the laser, refer to “Section 3: Operating Instructions” of the operator’s 

manual.

4. Precautions for Using the Variable Pulse Width Laser

When operating at a high voltage, the flashlamp will break and/or the mirrors will 

become damaged if the voltage is decreased and the pulse width is increased 

simultaneously. After operating the laser at a high voltage, either press “STOP” on 

the flashlamp controller to discharge the capacitors or fire the laser a few times at 

the lower voltage setting to stabilize the voltage in the charged capacitor before 

increasing the pulse width. 

Laser parts will become damaged if the voltage is deceased and the pulse width is 

increased because when the voltage is decreased, the capacitors are still charged at 

the higher voltage. Replacement part numbers for the flashlamp and the front and 

back mirrors are listed in the following Table. The front mirror from CVI is 

1/4 inch thick, but the original front mirror in the laser was 3/8 inch thick. The 

energy output did not change when the 3/8-inch-thick mirror was replaced with the

1/4-inch mirror.

Table. Replacement parts for the items in the variable pulse width laser head

Item PN Description Company

Flashlamp EM1687 High performance Fenix Technologies

Back mirror Y1-0537-0-3.00cc

0.5-inch diameter, 3-m 

radius, 3/8 inch thick, 

1,064 nm

CVI

Front mirror PR1-1064-30-0525

0.5-inch diameter, 

1/4 inch thick, R=30%, 

1,064 nm

CVI
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The flashlamp controller has an internal pump energy safety limit (set to 300 J), 

which was programmed into the controller to protect the flashlamp. If the safety 

limit is increased, the life expectancy of the flashlamp will decrease. 

5. Alignment of the Variable Pulse Width Laser

The laser needs to be aligned regularly to ensure the energy output is maximized. 

Procedures for completing a coarse adjustment and a fine adjustment are outlined 

in Steps 1–5. First, in the flashlamp controller, set the pulse rate mode to “single 

shot” and set the laser voltage to 250 V and the pulse width to 10,000 μs. Place an 

energy meter in front of the laser, and fire the laser to observe the measured energy 

output. If the meter was not triggered, adhere to the following steps (beginning with 

Step 1) to conduct a coarse adjustment. If the meter was triggered, skip to Step 5 to 

conduct a fine adjustment to try to increase the energy output. 

Step 1: Disconnect power

When aligning the variable pulse width laser, follow these first steps: 1) turn off 

the laser, 2) unplug the power cord to disable the flashlamp controller, and 3) 

disconnect the power cord to the laser head.

Step 2: Alignment of diode laser

Take out 4 screws to remove the plate located on the top of the laser head. Take out 

4 more screws to remove the top piece of the pump chamber cover. As shown in 

Fig. 3, place a target directly in front of the variable pulse width laser and place a 

diode laser and iris directly behind the variable pulse width laser. Align the diode 

laser straight through the center of the ND:YAG rod and point it at the target. Make 

sure the laser spot on the target is at the same height as the diode laser (i.e., beam 

is horizontal). The purpose of the iris is to decrease the diameter of the diode laser 

beam, making it easier to visualize reflections. 

Fig. 3 Setup for alignment of variable pulse width laser
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Step 3: Mirror adjustment

The front and back mirrors on the variable pulse width laser are aligned by 

adjusting the alignment screws on the mirror mounts to converge all reflections 

from the diode laser. Each mirror mount has 2 screws, one for vertical alignment 

and one for horizontal alignment. Place a beam block between the back mirror 

and the rod to observe reflections on the iris from the back mirror. Adjust the 

alignment screws on the back mirror such that all reflections are converged to 

the center hole of the iris. Then place the beam block between the rod and the 

front mirror and observe additional reflections that appeared on the iris. If 

additional reflections appeared on the iris, repeat Step 2 and Step 3 to make sure 

the diode laser is directed straight through the ND:YAG rod. Remove the beam 

block, and adjust the front mirror to converge all reflections to the center of the 

rod.

Step 4: Assemble laser

Once all reflections have been positioned to the center (in line with the diode laser), 

assemble the variable pulse width laser head by screwing in the pump chamber 

cover and the top plate. Plug in the flashlamp controller, and plug the power cord 

into the laser head and turn on the laser. Set the laser voltage to 250 V and the pulse 

width to 10,000 μs, and place the energy meter in front of the laser. 

Step 5: Fine alignment

Fire the laser and observe the energy output on the energy meter. Make very small 

adjustments to one of the alignment screws and refire the laser. If the laser energy 

increased, continue rotating the screw in the same direction, making very fine 

adjustments (the energy is very sensitive to rotation of the screws). If the laser 

energy decreased, rotate the screw in the opposite direction. Continue adjusting the 

screw until maximum energy is observed by the energy meter. Repeat this process 

on the remaining 3 screws until the maximum energy has been attained for all 4 

screws (2 on the back mirror and 2 on the front mirror). Refer to Fig. 2 to compare 

the energy output. 

6. Conclusion

Safe operation tips were provided to prolong the life of the parts within the head of 

the variable pulse width laser. A technique was also provided to align the mirrors 

of the laser for maximum energy output. The maximum energy of the variable pulse 

width laser increased as the pulse width increased up to 2.6 ms, at which point the 

maximum energy decreased as the pulse width continued to increase. The 

maximum energy output of the laser, as of 4 December 2015 was 7.7 J. 
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7. References

1. Barrows AW, Forch BE, Beyer RA, Cohen A, Newberry JE. Laser ignition in 

guns, howitzers and tanks: the light program Aberdeen Proving Ground (MD): 

Army Research Laboratory (US); 1993 Feb. Report No.: ARL-TR-62.

2. Forch BE, Barrows AW, Beyer RA, Newberry JE, O'Reilly JJ. Trends 

observed in the laser ignition of blackpowder and JA2 propellant. Aberdeen 

Proving Ground (MD): Army Research Laboratory (US); 1994 Mar. Report 

No.: ARL-TR-370.

3. Howard SL, Beyer RA, Cohen A. Direct laser ignition of gun propellants: 

simulator tests to screen candidate propellants. Aberdeen Proving Ground 

(MD): Army Research Laboratory (US); 1998 July. Report No.: ARL-TR1715.

4. Cohen A, Beyer RA, McNesby KA, Kotlar J, Whren A, Newberry JE. Model 

validation for high-power laser ignition of JA2 propellant. Aberdeen Proving 

Ground (MD): Army Research Laboratory (US); September 1999. Report No.: 

ARL-TR-2044.

5. Howard SL, Morris JB, Beyer RA, Hamlin SJ, Martin JF, Burke GC, Doris T.

Laser initiation thresholds of selected pyrotechnic and mic compounds for 

medium-caliber ammunition. Aberdeen Proving Ground (MD): Army 

Research Laboratory (US); 2006 June. Report No.: ARL-TR-3818.

6. Morris JB, Beyer RA, Hamlin SJ, Martin JF, Burke GC. Laser ignition 

thresholds of several aluminum/molybdenum trioxide metastable 

intermolecular composites. Aberdeen Proving Ground (MD): Army Research 

Laboratory (US); 2004 Sep. Report No.: ARL-TR-3308.

7. Gottfried JL, Munson CA, Colburn J, Beyer RA. Initial testing of a prototype 

laser ignition chamber. Aberdeen Proving Ground (MD): Army Research 

Laboratory (US); 2014 Mar. Report No.: ARL-TR-6862.

8. Collins ES, Gottfried JL. Ignition of energetic materials containing 

nanodiamond using a long-pulse laser. Aberdeen Proving Ground (MD): Army 

Research Laboratory (US); 2016. In press.

9. Hamlin SJ. MegaWatt Lasers, Hilton Head Island, SC, Personal 

communication, 2014 July 16.
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