Old 07-07-2010, 06:07 AM #1
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Default Ultralasers Lab Style DHL-G500N 500mW analog 532nm green laser 'Ultrareview'

Ultralasers 500mW 532nm Green DPSS Laser
Model DHL-G500N
July 5th 2010



Introduction:

This is a review of a single unit from the laser manufacturer/assembler Ultralasers. They have recently introduced themselves to the PL forum as a new provider for laser modules, and requested that a forum member perform an unbiased review and post it for all to see. Due to the test systems available and previous reviews I have done, I was selected to perform a review of a 200mW laser, but because of the introduction of relatively inexpensive 445nm, I requested to perform a review on the 500mW model. The test procedures in this review are selected to give a detailed example of how the laser will operate in a show like environment, and specific tests are done to look at modulation quality. A manufacturer submitting their laser to these tests is a good sign of confidence in their product. It is assumed that the laser reviewed here is exemplary of lasers of similar make and model being delivered by Ultralasers at this time. While I made every attempt at accuracy, other lasers purchased from this manufacturer may differ from what is seen in this review. Certain measurements made in this review cover laser properties not specified in datasheets nor commonly measured in the laser show industry, so the reader must decide the relative value of these measurements themselves.


Ultralasers DHL-G500N as seen on ultralasers.com

Arrival
The laser arrived from abroad in a folded cardboard box with DHL Daheng Laser markings, with closed cell foam padding protecting the laser inside. Both the power supply and the laser itself were loose in separate sections of the foam packing material. No instructions were included. Initially, no key was included, so I contacted Shawn and asked about it. He apologized and stated the shipping dept. must have forgotten to insert them and immediately sent a set of keys.


The Laser Box


The Laser Packing


The Laser Head with Anti-dust Tape


Laser Power Supply, Front


Laser Power Supply,Rear

General Description:
This laser module measures a smallish 4 ”x 2 ” at the base and 1 5/8” high. The power supply is likewise a tight little unit which measures in at 5 ” x 4 ” by 2” high. They are connected by a 13” umbilical which carries laser power and thermal control signals to and from the laser head. On the control unit are two switches: power on/off and laser on/off. The laser on/off keyswitch allows the stamped metal key to be removed in both off and on positions. The input power wire which accepts 100-260VAC is terminated in 3 stripped and labeled copper conductors for mounting to a screw terminal block: Line, Neutral, and Ground. Finally there is a ‘trigger’ wire for remote modulation control, the ends of which are marked + and -. Unfortunately, the mounting slots will not accept standard 1" centered optical table bolts, so some modification will be necessary if that is your goal.
The hardware of this module gave the impression of being relatively sturdy but light weight and small, and initially because of the size of the head and power supply I wondered if this was in fact the 500mW unit. The labeling clearly indicated that it was, so testing continued to find out if all that power could be packed into such a small case.

Operation and Power-up:
The analog modulation input line has an input impedance of 13.5k, comfortably high enough by itself not to load common ILDA DACs available on the market. An open circuit on this line results in a blanked laser, so if there is a broken modulation connection in your projector, the laser will remain off. The module has an approximately 4 second startup delay when powered up and when the keyswitch is engaged. Modulation speed is rated at 20kHz. After an initial warm-up time of 5 minutes, the laser idled at around 650mW output, a very pleasant surprise for a 500mW rated laser. Ambient temperature did not have a great effect on the output of this laser. The module fan and cooling fins with enclosed air ducts are sufficient to draw TEC heat away from the critical components and allow the thermal control system to stabilize at any ambient temperature tested: 75 to 90F. Even at high ambient air temperatures, the laser case only felt slightly warm to the touch.


Fig. 1: Startup and Stability.


Modulation Linearity:

Commonly, inexpensive analog DPSS lasers are modulated via a direct pump diode current control scheme. This results in a lasing threshold slightly above the minimum modulation voltage, which must be accounted for in laser show controller software. These tests are designed to assess the linearity of the output power with respect to the input modulation control voltage.

The first test protocol consisted of a continuous 5V command signal to the control module to warm up the laser, followed by 10-second periods where the laser was modulated with the desired test voltage, then back to full power (5V). The range of 0-5V was covered by 50 discrete test steps of 100mV each. Figure 2 show the resulting modulation curve.


Fig. 2: CW Modulation Linearity

The threshold voltage is just under 1V which is right where it should be for this type of laser. CW output power increased in a nearly linear fashion from 1.25V to 5V without any major drops in power. This is a good result for a DPSS laser. As a test, I increased the input voltage past 5V to characterize the input protection, and found that output power did not increase beyond 5V input, indicating this laser has good input modulation protection.

Pulse Modulation Linearity:

While the slow 10-second modulation period of the previous section was adequate to allow the Scientech thermal sensor to respond to the new laser power for measurement, this is not a realistic simulation of laser control signals during a laser show. These signals tend to be fast and of short duration, allowing little time for thermal equilibrium at each power level. A pulse modulation linearity test was devised in an attempt to better simulate the lasers response in laser show conditions. The laser modulation control voltage was held at 1V until the laser was warmed up, then a series of 10ms test pulses were generated at 0-5V in 100mV increments, and the resulting output power during each test pulse was sampled at high frequency, averaged, and recorded.


Fig. 3: Pulse Modulation Linearity.

The Ultralasers DHL-G500N showed remarkably good pulse modulation linearity. Given that the human eye can only detect changed in brightness of 5% or more, it would be difficult to perceive much if any nonlinearlity from this laser during operation. Peak modulation is attained at 4.8V, presumably where the module’s input protection begins limiting the input signal.

Graphs are great, but how does it perform in a real-world high speed test? I set the module up in my scanner system and photographed a scanned image from LaserCam. Ignoring the dark ring caused by the camera shutter timing, the high speed raster modulation is very good for a DPSS laser.



Blanking Pulse Response:

In order to test the stability of the laser power output in response to a blanking pulse, the laser was set to full power (5V) and allowed to warm up. Then, a 10ms blanking pulse was generated, and the lasers output was recorded for 180ms after this pulse using the high speed photo-detector. As a control, the response of a direct-injection 658nm laser controlled by a FlexMod laser driver was recorded (Fig 4). Having no temperature sensitive non-linear optics and optimized current control feedback of the FlexMod driver, the output power after the blanking pulse exactly matched that before the blanking pulse, with a sharp transition in output power and excellent stability. This is the ideal case blanking response.


Fig. 4: Ideal Case Blanking Response of Single Mode Laser


Fig. 5: Blanking Response of D.U.T.

Although Figure 5 shows significant power fluctuations after blanking, in practice, the effect is not strongly visible. Post blanking fluctuations did not surpass 14% of the total output power and lasted approximately 30ms. A second pulse test was performed, this time with the laser initially blanked, then the modulation line pulsed for 10ms at 2.5V.


Fig. 6: Pulse Response From Rest

The Device Under Test was able to reach within 10% of its output value quickly at the pulse onset, the succeeding fluctuations < 14% total output power. This also is a good result from a DPSS laser, indicating this DHL-G500N module is ready to handle any analog show application with ease.

Beam Quality:

The beam exits the laser aperture with a diameter of approximately 2mm and a measured divergence of 1.4 mrad. This exceeds the manufacturer’s minimum specifications of 2.5mm at the aperture and <2.0 mrad divergence. Beam spot was near-TEM01 as shown in Figure 7. The beam was vertically polarized with a ratio > 100:1, so PBS combining two of these modules for 1W of green is feasible. Scatter was minimal.


Fig. 7: Beam Shape at 40’

Conclusion:

In the end, its small size was not a detriment, but a bonus. The Ultralasers DHL-G500N 500mW 532nm laser performed very well, exceeding all specifications except beam mode. The power stability was good, and the pulse modulation linearity was very good. As expected, the modulation characteristics were vastly superior to the 473nm DPSS model previously reviewed. Over the testing period, the laser was operated for about fifty hours with no decrease in power output. It is my hope that the review process of future laser modules will be expanded to include some of the tests presented here, so that everyone would know what to expect in terms of beam and modulation quality. Suggestions for Ultralasers: 1) Modify the mount points to accept 1" centered, larger optical table bolts 2) verify lasing mode after tune-up 3) use a ball bearing cooling fan on the laser head instead of a sleeve bearing fan (if it is not already).

Acknowledgements:

Thank you, Ultralasers for loaning the laser for testing and being willing to undergo any testing proposed. Thanks also to PhotonLexicon for providing a rich community of laser hobbyists and professionals, and to Sam Goldwasser for his excellent laser FAQ!



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Old 07-14-2010, 02:12 AM #2
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Default Re: Ultralasers Lab Style DHL-G500N 500mW analog 532nm green laser 'Ultrareview'

very nice and complete review.... thank you!!!!
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