ML GRATINGS
ML gratings are original rulings or replicas that are normally used as end reflectors for tuning molecular lasers.

The output wavelength of a molecular or dye laser can be tuned by rotating a Littrow mounted grating around an axis parallel to the grooves. The grating equation:

nl = d(sin i + sin i')

where n is the order of diffraction, ? is the diffracted wavelength, d is the grating constant (the distance between successive grooves), i is the angle of incidence measured from the normal and i' is the angle of diffraction measured from the normal, reduces to n? = 2d sin i for the Littrow configuration.

The angle of incidence (i) is adjusted to select the output wavelength while creating a narrow gain profile.

Blaze Angle and Alignment
Because the ML series of gratings are designed for peak polarized efficiency, the groove angle is not equivalent to the Littrow blaze angle of the grating. As a result, when using a He-Ne laser for preliminary grating alignment, the brightest He-Ne order will not correspond to the blaze wavelength of the grating. The grating must be aligned using the calculated He-Ne order that corresponds to the wavelength of interest, regardless of its relative intensity.

The blaze arrow marked on the side or back of the grating should be oriented as shown below.

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Polarization
Typical efficiency curves illustrate that, in all cases, orienting the polarization of the E vector (P-Plane) perpendicular to the grooves (E?) increases the efficiency over a specific wavelength region. This should be considered when optimizing the figure of merit (Q) of a cavity, particularly when it is polarized by auxiliary components such as Brewster angle windows.

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Coating
ML gratings can be overcoated with gold, increasing the reflectivity at 10.6 microns by approximately 1%, but the damage threshold in high power applications may be reduced. No damage threshold minimums apply for overcoated gratings.

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Molecular Laser (ML) Gratings

ML (Molecular laser) Series replicated ruled gratings are used primarily to tune the output wavelength of high powered lasers. High peak efficiencies, typically from 92%-96%, are achieved by orientating the polarization of the "E" vector perpendicular to the grooves rather than the unpolarized average. Original MLs are ruled directly into an aluminum coating on a copper substrate, resulting in an inherently high damage threshold.  Standard MLs are available in a number of blaze wavelengths (2.8 μ to 16.0 μ) and groove spacings (75 g/mm to 450 g/mm).

Summary ML Grating Specifications
Model No.	Grooves MM	Min. Polarized Abs. Efficiency	Optimum Range (μ) (nm/mr)	Angular Dispersion	Eff Curve
ML-301	75	≥ 88%	9.0 - 11.0	12.3
ML-302	100	≥ 88%	9.0 - 11.0	8.5
ML-303	150	≥ 88%	9.0 - 11.0	4.2
ML-304	138	≥ 88%	9.0 - 11.0	5.2
ML-401	150	≥ 88%	5.0 - 6.0	6.1
ML-402	300	≥ 82%	5.0 - 6.0	2.0
ML-501	300	≥ 80%	2.5 - 3.0	3.0
ML-502	450	≥ 85%	2.0 - 4.0	1.6
ML-601	300	≥ 80%	2.5 - 4.0	0.35
ML-701	90	≥ 88%	16.0 - 20.0	7.7

ML Grating Replicas - Rectangles
Model No.	12.5 x 25 mm REPLICA CAT. NO.	25 x 50mm REPLICA CAT. NO.	1 x .825 REPLICA CAT. NO.	Eff Curve
ML-301	5-3810	5-3113	5-3118
ML-302	5-3820	5-3123	5-3128
ML-303	5-3830	5-3133	5-3138
ML-304	5-3840	5-3143	5-3148
ML-401	5-4810	5-4113	5-4118
ML-402	5-4820	5-4123	5-4128
ML-501	5-5810	5-5113	5-5118
ML-502	5-5820	5-5123	5-5128
ML-601	5-6810	5-6113	5-6118
ML-701	5-7810	5-7113	5-7118
Prices ($)*	120.00	230.00	130.00

* Prices are in USD and are list prices only.

ML Grating Replicas - Squares
Model No.	25 x 25 mm REPLICA CAT. NO.	30 x 30mm REPLICA CAT. NO.	50 x 50mm REPLICA CAT. NO.	58 x 58mm REPLICA CAT. NO.	Eff Curve
ML-301	5-3112	5-3119	5-3115	5-3116
ML-302	5-3122	5-3129	5-3125	5-3126
ML-303	5-3132	5-3139	5-3135	5-3136
ML-304	5-3142	5-3149	5-3145	5-3146
ML-401	5-4112	5-4119	5-4115	5-4116
ML-402	5-4122	5-4129	5-4125	5-4126
ML-501	5-5112	5-5119	5-5115	5-5116
ML-502	5-5122	5-5129	5-5125	5-5126
ML-601	5-6112	5-6119	5-6115	5-6116
ML-701	5-7112	5-7119	5-7115	5-7116
Prices ($)*	180.00	190.00	290.00	350.00

ML Grating Replicas - Diameters
Model No.	25 mm DIA. REPLICA CAT. NO.	38 mm DIA. REPLICA CAT. NO.	50 mm DIA. REPLICA CAT. NO.	Eff Curve
ML-301	5-3111	5-3117	5-3114
ML-302	5-3121	5-3127	5-3124
ML-303	5-3131	5-3137	5-3134
ML-304	5-3141	5-3147	5-3144
ML-401	5-4111	5-4117	5-4114
ML-402	5-4121	5-4127	5-4124
ML-501	5-5111	5-5117	5-5114
ML-502	5-5121	5-5127	5-5124
ML-601	5-6111	5-6117	5-6114
ML-701	5-7111	5-7117	5-7114
Prices ($)*	240.00	365.00	495.00

Coatings

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Efficiency Curve Key

• All gratings are measured in the Littrow mounting in 1st order
• All gratings utilize an aluminum (AI) reflective coat

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